Why aren’t we talking more about airborne transmission? | Hacker News Reader

Why aren’t we talking more about airborne transmission?

theatlantic.com

301 pointsKoftaBob279 comments

After this pandemic, doctors and scientists are going to have to come up with more media-friendly terms from now on.

The problem is that "airborne droplets" and "airborne" sound too similar and it's very hard for regular people to understand what that means. "Airborne droplets" means that viruses need saliva to transmit between people. "Airborne" means that the virus only needs dust particles to transmit to other people. Measles is airborne transmission, which means that if someone with measles enters a room, that room can be infectious for 12+ hours because viruses will be infectious in the dust. If someone with coronavirus sneezes in a room, the large heavy droplets will quickly fall to the ground. If you breathe in the droplets then you can catch the virus, but these only stay in the air for seconds. However, there are microdroplets which stay in the air for 30+ minutes depending on the air currents.

So there is a distinction between them. If coronavirus were truly airborne, then we would all need to wear masks all the time, even when no one is around. No where would be safe and we would have to implement extremely strict lockdowns.

But the fact that scientists and doctors have chosen to use the term "airborne" in both have made it extremely confusing and given how quickly information and misinformation is disseminated these days, they need to choose terms with care from now on.

The article addresses this midway through. The problem is that even the experts haven't really agreed on terminology. They need to do that first before they can hope to inform the public. :)

So why talk about HVAC systems ?

Context:

>” by 10 bottles of hand sanitizer without a word on ventilation—whether it was opening windows, employing upgraded filters in its HVAC systems, or using portable HEPA filters. It seems baffling that despite mounting evidence of its importance, we are stuck practicing hygiene theater...”

Sorry, what do you mean?

I suspect the parent post meant "why not", as in "improving HVAC would be more effective than the omnipresent hand sanitizer, so why aren't we talking about that?"

One important point that comes out of this is that few people are stressing shoe sole hygiene. Not necessarily meaning that one has to scrub them often, but to be mindful of what it touches (car interior mats, mats at home and possibly if people don’t take off their shoes, all over the house, hands taking off shoes, shoe racks, etc.) Given that droplets mean the virus will accumulate on floors and such surfaces.

A place to put outside shoes and put on inside slippers (flip flops in my case) is good for clean floors anyway. I highly recommend, whether that’s a little mudroom or just a walled rubber/plastic container to take off shoes.

That said, I’m not sure it does much for this particular virus, but it can’t hurt and your floors (especially carpets, but those are nasty anyway) stay much cleaner.

why would that matter? transmission from surfaces is apparently quite low, and it doesnt last long on surfaces, and its not like im touching / eating off anything my shoes come into contact with anyway. This feels like an incredibly low risk vector

Low but greater than the “aerosolized” vector. When people sneeze, it land on surfaces (like floors), when they cough, etc.

If surfaces were not a problem, we wouldn’t be using wipes and sanitizers. So why ignore one possibility and stress another?

When people take off their shoes they can get contaminated. If they have pets the pets will pick some up and get it on you, etc.

The incessant use of wipes and sanitizers is basically "Hygiene Theatre" [1].

> In May, the Centers for Disease Control and Prevention updated its guidelines to clarify that while COVID-19 spreads easily among speakers and sneezers in close encounters, touching a surface “isn’t thought to be the main way the virus spreads.” Other scientists have reached a more forceful conclusion. “Surface transmission of COVID-19 is not justified at all by the science,” Emanuel Goldman, a microbiology professor at Rutgers New Jersey Medical School, told me.

[1] https://www.theatlantic.com/ideas/archive/2020/07/scourge-hy...

The solution here : don't lick the floor.

Understood but think pets and of children who could later carry it to you.

I don't want to minimize Covid - of course you must protect yourself as you see fit.

> we would have to implement extremely strict lockdowns...

if we assume that the goal is not to flatten the curve but to completely stop the virus in its tracks. Most people and countries don't have this goal.

Edit: To those downvoting, I'll just say that my statement is factual, so argue the facts. Long-term, we want a vaccine, yes. In the meantime, most people and countries are simply not willing to do what it takes to completely eliminate this virus. They think it would be nice if the virus went away, but they are not working towards that as their goal.

> Edit: To those downvoting, I'll just say that my statement is factual, so argue the facts.

I wonder if the downvotes were caused by the phrasing of this statement:

> Most people and countries don't have this goal.

At first I thought you were saying that people didn't actually want to stop the virus in its tracks.

It took me a minute to realize that you're saying people have accepted full-stoppage-in-tracks as being infeasible, and therefore don't consider it an attainable goal.

> At first I thought you were saying that people didn't actually want to stop the virus in its tracks.

No, I think that's precisely what they were saying. I don't think that this is unattainable - I think it would have a greater economic cost, particularly to the wealthy, than many countries are willing to bear. It's not unattainable - it would cost them more than those lives are perceived as being worth. Big conceptual difference.

It's not only economic cost. To get results like in china you have to be (like) china. It's easy to sell drastic measures to the population if the infection (and death) numbers look scary. But if the numbers stagnate at low values nobody is going to accept drastic measures. You would need to fight against your own population to stop the virus altogether. And even if you achive this, the virus will return (tourist/travelers).

If the virus were truly airborne, which it isn't, then simply walking through an empty room could get you infected. The levels of people getting infected, and subsequently getting hospitalized would be far worse than the worst scenes we saw in Italy and NYC. Lockdowns absolutely would have been mandatory for months upon months.

Coronavirus is not by itself a tremendously deadly disease. The problem is how infectious it is, and how quickly it can overrun a limited hospital system. Even at a sub-10% hospitalization rate for people younger than 60, we are seeing many hospitals getting full. It being truly airborne would make things worse by many orders of magnitude. The way coronavirus spreads is basically the same mechanism as the flu and the cold, yet the levels of people getting infected are much much worse. Imagine if simply walking through a room could get you infected. The spread would be undeniably worse than anything we had every seen before. Even stores like Costco and all factories would have to shut down. So yes, very strict lockdowns would need to be in place.

Thank goodness it's not.

Um.. it is airborne, that is why there are multiple super-spreader events that can’t be explained by someone interacting within 3-6 feet for 10 minutes. (e.g. cases of 1 to 100, 1:500 case reported as well).

If you walked into an empty hospital room that was just used with high air-virion density, you could get infected, that is why they decontaminate with the equipment you see.

I think the main reason this isn’t being communicated is because we will never have enough N95 masks to mitigate this (would need 5-10 years of 24/6 production to fill govt. stockpiles).

I would bet that you are right, but it is still a controversial opinion, and droplet transmission is probably still a major factor. Plenty of research supports the claim, although some studies conclude that it is only significant when the spreader has a high viral load:

https://www.nature.com/articles/s41598-020-69286-3

https://jamanetwork.com/journals/jamanetworkopen/fullarticle...

https://www.medrxiv.org/content/10.1101/2020.07.16.20155572v...

https://www.medrxiv.org/content/10.1101/2020.07.13.20153049v...

Ok - these multiple superspreader events... do you mean 100's or 10's or a few? And when you say "can't be explained " really? Can you provide some back up to this information?

https://jamanetwork.com/journals/jamanetworkopen/fullarticle...

https://www.vox.com/21296067/coronavirus-covid-symptoms-supe...

(put the air purifiers in the bathroom it seems...)

thanks for continuing to tease out the nuance. nearly all coverage and discussion of covid is an exercise in frustration, one way or the other.

the unrealistic desire for riskless, surefire mitigations had led us exactly into the ping-ponging uncertainty that such longing tries so strenuously to avoid. it's wreaking havoc on our social and economic lives, let alone politically.

taking into account what we know so far, the best bang-for-buck rule is still "distance (inside), and when you can't, mask.", not shutdown, or mask outside and all the time, or never mask or distance, or business as usual, or wipe down surfaces incessantly, or reconfigure every hvac system.

the simplicity of that one rule belies a lot of understanding packed into it, unfortunately, leading to an unnecessary yearning for more. there isn't more that we ordinary folks can do than that. that's not to say don't be cognizant of the progress we're making, but does suggest we need to stop fretting while we wait for more effective treatments, herd immunity, and/or a vaccine.

> If the virus were truly airborne, which it isn't

why do you say this? The article is saying otherwise, quite literally "The coronavirus reproduces in our upper and lower respiratory tracts, and is emitted when we breathe, talk, sing, cough, or sneeze"

> then simply walking through an empty room could get you infected

You're presuming it has to be empty.

If you walked through a full room without touching anyone or anything and you caught covid, would you accept that it is airborne? Or are you saying that is impossible?

Do I misunderstand you?

Yes you are misunderstanding me.

That's where the six feet distance part comes in.

It’s because it seems to be mostly ballistic droplets, except for a (small?) percentage were it is not. This is also stated in text for measles (that spreads throughout a house) which Corona seems to not do.

From the article, that's exactly what's being questioned:

"There is a big dispute in the scientific community, however, about both the size and the behavior of these particles, and the resolution of that question would change many recommendations about staying safe. Many scientists believe that the virus is emitted from our mouths also in much smaller particles, which are infectious but also tiny enough that they can remain suspended in the air, float around, be pushed by air currents, and accumulate in enclosed spaces"

Yes but, and this is the important part : not as potent as for instance measles (which spreads and infects 90%)

Or we’d see far more indoor cases. And we do see in events with lots of expiration, where there is singing for example, very potent transmission.

You don't seem to be engaging with the "airborne on droplets" vs "airborne aerosol" vs "airborne on dust" discussion that spawned this subthread.

>Even stores like Costco and all factories would have to shut down.

That would kill a lot of people too. It's not obvious to me which would be worse, particularly in the face of such a low IFR.

WTF is going on here?

You claim "If the virus were truly airborne, which it isn't" yet provide no evidence.

But looking at you history you have provided exactly evidence that it is airborne "Video showing microdroplets suspending in air (vimeo.com)" a few months ago (https://news.ycombinator.com/item?id=22776194)

And to quote from another commenter "The part showing how a single cough can create a room-wide cloud of virus that lingers for 20+ minutes in spaces with poor circulation was especially enlightening."

Having watched the vid I can confirm that's what they show, at least as a simulation.

Even the main article says (I'm re-quoting from another of my posts): "There is a big dispute in the scientific community, however, about both the size and the behavior of these particles, and the resolution of that question would change many recommendations about staying safe. Many scientists believe that the virus is emitted from our mouths also in much smaller particles, which are infectious but also tiny enough that they can remain suspended in the air, float around, be pushed by air currents, and accumulate in enclosed spaces" which directly opposes what you say.

How is your parent post not either plain wrong or deliberately sowing confusion? I'm flagging you.

> I'll just say that my statement is factual

> assume

> goal

An assumption is not a fact. A goal isn't a fact either.

While total elimination is probably impossible, plenty of places have managed almost complete suppression to the point where it's more like E. Coli; occasional outbreaks, but action taken to contain it.

"flatten the curve" is now associated with "herd immunity" and other discredited ideas.

I think you may have responded a little hastily and misunderstood the comment.

---

> An assumption is not a fact.

Correct, and the person you were replying to never implied that it was. I'll rewrite the comment more explicitly for you, instead of using the implied context of the quotation:

> If the goal was not to flatten the curve but to completely stop the virus in its tracks, we would have to implement extremely strict lockdowns. Most people and countries don't have this goal [to completely stop the virus]

---

> A goal isn't a fact either

"Entity X has goal Y" is, indeed, a fact. (EDIT: Or, rather, a statement - which may or not be factual) The person you were replying to claims "Most people and countries do not have the goal to completely stop the virus" as a fact. Neither you, nor they, have provided evidence for or against the factuality of this statement.

---

Can you elaborate on what, exactly, is discredited about "flattening the curve" - shorthand for "reducing the rate-of-increase of new cases, so that the throughput of new cases is within the carrying capacity of the country-in-question's medical infrastructure"?

Almost all countries are pursuing a herd immunity strategy by default, just at varying rates. Only a handful of countries are actually taking steps to eradicate the virus within their borders.

The whole "flatten the curve" messaging always seemed like we were barreling toward a misunderstanding, and I think this comment and the disagreeing downvotes are a perfect example of that.

Back when US public health messaging really went all-in on that phrase it was like late February when we thought the transmission level was minimal. "Flattening" the curve at a minimal level would have been fine, and if we got the reproduction rate even just barely below 1 the infection would have died out.

Flattening the curve when there are 10,000 people dying a week is a very different situation, and I don't think ending up there was ever explicitly anyone's goal (except for famously Sweden). But that's what we finally ended up achieving in April, and everyone basically patted themselves on the back for it and started treating the pandemic as over. It should have been very clear to anybody paying even a little bit of attention that once we started approaching and then surpassed "running out of ICU beds"-level of crisis in some places, that flattening the curve anywhere near that level would not be good, and when we did start to plateau at only like 30% down from the peaks we were nowhere near in the clear. But for whatever reason we just ignored that inconvenient fact and acted as if our lockdown had worked. After all, we had "flattened the curve".

Obviously the world is quite complicated and this is impossible to predict, but I genuinely wonder what would have happened if a more ambitious catchphrase had caught on instead like "zero out the curve". It's well-known that laypersons are naturally bad at reasoning about exponential growth, but I also think the public health "experts" really let us down as well in their failure to properly account for the exponential growth as well.

Flattening the curve was about preventing the hospital system from being overwhelmed. It was about solving the crisis from the point of view of civic administrators and politicians. So, keeping people safe was a secondary goal: the primary purpose was to keep the system from failing outright.

IMHO, consequent to the misinterpretation of this, people assumed that if the curve was flattening, the problem was being solved, since they thought that the curve was about their safety, rather than about stretching the deaths out so that queues didn't form.

I don't agree with your conclusion. Airborne is airborne regardless of whether it's 5 minutes or 12 hours. The point of the word is to tell people that you can become infected without being in direct physical contact with them. Trying to come up with words for different durations of airborne is only going to make it more confusing, even if it becomes less ambiguous to the people who know the difference between the terms.

I disagree. You need to treat the virus at the right level of concern otherwise you lose credibility. As we can all see, credibility from the experts needs to be maintained, otherwise no one trusts them anyone. The whole fiasco with masks is because the experts told us things that were obviously wrong at the beginning (ie. masks don't work, masks won't help regular people, etc).

If there is airborne droplet transmission, which I believe is the case otherwise we wouldn't get such infectious spread in bars, etc, then we need to implement better ventilation, social distancing and mask wearing and probably goggles too.

If it was truly "airborne", which it isn't, then the measures would need to be much, much more draconian otherwise it would spread much quicker.

> You need to treat the virus at the right level of concern otherwise you lose credibility.

I agree with this but don't see how the use of the word "airborne" conveys concern. Maybe this is some american hollywood trope now that I remember reading the phrase "It's airborne!" in the original article? Wikipedia's article on airborne diseases certainly don't seem to imply that there's a strict definition of how long a pathogen has to survive in the air for it to be classified as airborne.

> As we can all see, credibility from the experts needs to be maintained, otherwise no one trusts them anyone.

While I agree with this, we're in an age of misinformation and macho power culture where saying "we're not sure yet so let's just be as careful as possible" apparently doesn't do much good in many places of the world. And I don't think a technically incorrect use of a word like airborne is NEARLY as significant as changing stances on masks and presidents endorsing quacks.

> If it was truly "airborne", which it isn't, then the measures would need to be much, much more draconian otherwise it would spread much quicker.

You need to make up your mind here, are you talking to professionals, or lay people?

To lay people the term airborne means it spreads by air... which is what it does. The fact that it doesn't linger in the air for 12 hours is secondary and would need to be addressed in whatever policy is put in place.

Since we don't need lay-people to understand what the virus isn't, the term airborne is just fine.

It's possible, if annoying, to simply wait 5 minutes between trips while the elevator car's air clears. It has to be handled differently (eg using a fan) if it would take 12 hours for the air to clear.

Given that we are all talking about COVID-19, as caused by the SARS-Cov-2 virus, (and not any other disease), the exact word or phrase used in popular media is less important, what's important is for people to recognize that breathing someone's are 5 minutes later is hazardous. Would you even know if there was person in the same elevator car as you 5 minutes before you came along? How can you recognize if they were actively symptomatic and positive and not wearing a mask. What it's called by scientists is less important compared to outright science denial going on.

Even before "global warming" was renamed "global climate change", people are able to learn and understand the phenomena that it refers to, even if there are idiots that say "global warming isn't real" because they felt cold at some point. With today's instant access to information, I want to push back against the idea that everybody who cares to ask is too dumb to learn the difference between "airborne" (12 hours) vs "airborne droplets" (5 minutes).

I propose calling airborne droplets “germ infested mouth farts”. It’d definitely get the 4 year olds on board.

That's pretty disgusting and vulgar. Let's not.

that's pretty disgusting and vulgar. I'm down!! :)

Is a better distinction Dry Airborne vs Wet Airborne? There is still particle size to consider I guess.

My friend uses "aerosols" for the latter term

> If someone with coronavirus sneezes in a room, the large heavy droplets will quickly fall to the ground.

This is the slightly incorrect part with COVID.

Traditionally, this would be an appropriate description for other droplet transmission (like the flu). However, it seems COVID has an above average ability to survive in extremely fine droplets - think mist-sized particles that CAN float in the air for an extended period of time (given the right circumstances).

This nuance is challenging to convey. For healthcare workers, it's important because it likely means standard droplet based precautions are not enough. However, it also seems that full airborne precautions (PAPR's) are overkill. My take is N95's do enough to dehumidify droplets and ultimately break down particles.

For the general public, the nuance is less important. Most don't have access to proper fitting N95 (or better) masks, so they're stuck wearing cloth or surgical masks. They should simply think of COVID as airborne because they're likely not wearing the proper gear.

I don't see what was incorrect about the parent.

It goes on to say "However, there are microdroplets which stay in the air for 30+ minutes depending on the air currents."

It sounds like you're both in agreement that large droplets fall quickly to the ground, and that with COIVD the longer-lasting micro-droplets are a relevant factor.

Am I missing a subtlety?

There are no "microdroplets" which stay in the air for "30+" minutes.

First, water DRIES OUT unless the humidity is very close to 100% which is relatively rare in western countries. The smaller droplet the faster this happens.

Put a very, very small droplet on a flat surface like glass. Observe it disappear within couple of minutes. Then imagine that a smaller droplet is just larger droplet closer to drying out.

Volume increases with cube while surface with square of diameter. When the droplet gets smaller the drying out speeds up.

The only time there are persistent droplets of water in air is called fog and happens when air is supersaturated with water. This happens when you cool air that is already 100% humidity. In that circumstance water cannot evaporate and that is what makes it possible to have water droplets in air. Once the relative humidity falls below 100% even a tiny bit, the fog almost instantly disappears.

Ability of virus to be airborne means it can survive outside droplet of bodily fluid for an extended period of time. Once all water dries out it also becomes very light and can be moved by smallest currents of air.

I suggest you educate yourself on the topic of microdroplets.

https://www.weforum.org/agenda/2020/04/coronavirus-microdrop...

I suggest you educate yourself.

https://en.wikipedia.org/wiki/Airborne_disease

"Airborne transmission is distinct from transmission by respiratory droplets. Respiratory droplets are large enough to fall to the ground rapidly after being produced (usually greater than 5 μm), as opposed to the smaller particles that carry airborne pathogens. Also, while respiratory droplets consist mostly of water, AIRBORNE PARTICLES ARE RELATIVELY DRY, which damages many pathogens so that their ability to transmit infection is lessened or eliminated."

Here, I capitalized it for you so you don't miss it.

Airborne virus is what happens after fine respiratory mist dries out, which happens quite quickly. It is "relatively" dry because some of the respiratory fluid is hygroscopic. Don't make a mistake, there is no free flowing liquid with virus happily swimming in it.

Thank you, you're repeating things I've already stated in my first post. I suggest reading things more carefully.

In your refusal to read the article, you're missing how sars-cov-2 is teaching us new science about how viruses may survive in aerosols, which behave differently from particles that travel in a ballistic motion.

Airborne viruses have been known for a long, long time. The physics is established. The whole reason we distinguish between airborne and non-airborne viruses is exactly because virus needs special arrangements to be able to survive outside of fluid.

While it is interesting how particles move in a room, it is completely different topic. The particles ARE NOT AEROSOL. The kind of aerosol that can flow in tiny air currents dries out in seconds and becomes small particles (not droplets) of "relatively dry" matter that is fine enough to stay in air for a very long time.

These threads are awful because "droplet" and "aerosol" don't have good fixed definitions, and because people misuse the word "airborne" to mean "aerosol".

Yes, there is a lot of education problem when you want to discuss anything virus related.

Aerosol == small droplets of water.

Airborne, particles == no droplet, just leftover of an aerosol that dried out in less than 100% humid air.

It would not be the first time that health-related article on an economic website gets physics wrong.

I appreciate the distinction you're making here. I don't have enough facts to prove or disprove it.

But, I'd like to ask: are you suggesting that aerosolized droplets cannot be seriously spreading this disease because they will evaporate almost instantly?

I ask because there is quite a bit of research suggesting that aerosolized droplets are spreading the disease, and can hang int the air for a substantial period of time. Do you think this is wrong? If it is wrong, why do you believe people are suggesting aerosolized transmission?

Well... I am not suggesting anything.

There are two types of viruses: airborne and not airborne. Airborne can survive for some time outside bodily fluids.

Aerosol == bodily fluid that is still liquid. It is just in the form of very small droplets that are now drying out. Depending on conditions this lasts very shortly. It spreads the virus, of course, but aerosol dries out quickly and viruses that are not airborne die (well.. viruses do not live in the usual sense, basically their proteins get damaged).

Of course if somebody coughs in your direction some of the aerosol can be inhaled or reach your retina or get on your hands and you can get infected.

No, I am not suggesting droplets cannot spread the disease, the opposite is true. Droplets are much better transmitter of disease if they can reach the target.

True. And I am curious whether things can be done in most building's HVAC systems to account for this.

The ideal would be:

- Heavy external air exchange OR heavy filtering (think N95-level filtration on the return air exchange

- Diffusers are at foot level (not common)

- Return air in ceiling

- People wear masks

My fear of school spread is that folks are basing their mental models on the flu, and if this hangs in the air for an appreciable amount of time then classrooms are difficult to keep sanitized.

Good luck out there. Thanks for the knowledgeable comment.

"However, it seems COVID has an above average ability to survive in extremely fine droplets - think mist-sized particles that CAN float in the air for an extended period of time (given the right circumstances)."

This is one of those "facts" that is often repeated, but which has little actual evidence if you bother to look for it. The WHO has been consistent that aerosol transmission of the virus is a theory with little backing evidence:

Some outbreak reports related to indoor crowded spaces have suggested the possibility of aerosol transmission, combined with droplet transmission, for example, during choir practice, in restaurants, or in fitness classes. In these events, short-range aerosol transmission, particularly in specific indoor locations, such as crowded and inadequately ventilated spaces over a prolonged period of time with infected persons cannot be ruled out. However, the detailed investigations of these clusters suggest that droplet and [transmission from contaminated surfaces or objects] could also explain human-to-human transmission within these clusters."

"Current evidence suggests that SARS-CoV-2 is primarily transmitted between people via respiratory droplets and contact routes – although aerosolization in medical settings where aerosol generating procedures are used is also another possible mode of transmission"

https://www.who.int/news-room/commentaries/detail/transmissi...

ARS did a pretty good job of summarizing the (IMO terrible) mass-media reporting on this issue:

https://arstechnica.com/science/2020/07/no-the-who-has-not-r...

> although aerosolization in medical settings where aerosol generating procedures are used is also another possible mode of transmission

I'm married to a physician and have been primarily following this through the eyes of her and her peers. In an acute care setting, aerosolization is a huge concern. It's a big factor between being able to get away with a surgical mask/face shield and requiring significant PPE.

In daily life, this probably isn't a huge concern (or a significant means of transmission at a public health level).

Sure, absolutely. If you're in the business of intubating people on a daily basis, then it's a real concern.

This is what the article challenges.

The author provides cases of events where infection by droplets cannot entirely explain the spread.

The WHOLE POINT of the article is to educate you about the difference between droplets (ballistic) and aerosols (behave like a gas).

It doesn't look like you, or the people replying to you read the article. And thats a shame, because you're exactly the type of person who the author is trying to educate.

I believe that’s why the parent comment said scientists and medical experts should improve how they explain terms going forward. People like OP should not be this confused about how the virus spreads after 4 months of hearing about it all the time. I’m glad we have magazines helping fix that problem now, but communication from places like the CDC hasn’t been totally understandable to normal people. (Add a healthy dose of misinformation and propaganda and you get today’s situation :))

Please read and follow the site guidelines. You broke several of them here, and have been doing so elsewhere also.

https://news.ycombinator.com/newsguidelines.html

> If coronavirus were truly airborne, then we would all need to wear masks all the time, even when no one is around.

Cloth masks wouldn’t protect against that. Masks don’t do anything to stop airborne spread, only potentially mitigating droplet spread.

Unless you are referring to biohazard respirators as “masks.”

This is a bit of an outdated view on Coronavirus though. The whole point is that “airborne” isn’t black and white (which is how the WHO has treated it) and is more of a spectrum. A large number of scientists have been lobbying the WHO to get them to talk about it as airborne because it’s not just heavy droplets like people thought in the beginning. And there’s real concern that viral load can build up in poorly ventilated spaces. Which is why it’s a good idea to spend as little time in closed public spaces as possible, and why Fauci suggests that if you’re someone who needs to avoid it at all costs, then goggles are probably a good idea.

This is why science communicators are extremely important. Technical words are great for trained professionals who understand the context. But too many people, myself included, repeat these words only partially understanding what they're intended to mean.

More important would be fixing the messaging on masks and protection. (Most laymen aren't going to distinguish between droplet, aerosol, airborne, etc. and won't adjust behavior and risk profiles accordingly.)

The CDC told people that masks were not important at the start of the pandemic, largely as a means of reserving stock for doctors and first responders. They then performed an uneven and awkwardly stilted 180 on that message. This massively backfired and led to wide scale public distrust of the public health apparatus. The birth of the anti-mask movement, etc.

We'll be living with the ramifications for a long time.

You shouldn't lie to the public.

> The birth of the anti-mask movement, etc.

Hogwash. Those people would have latched onto something else. The 1918 pandemic also had its "anti-mask" idiots.

Stupid is timeless and universal.

> You shouldn't lie to the public.

Agreed. Calling an active pandemic a "liberal hoax" started a huge problem.

You are being unfairly downvoted.

You are right in that the anti-mask movement did not start because the CDC reversed its position. (Thank you for citing 1918 as a supporting point.) The anti-mask movement started because everything in American politics has to be turned into a right-left culture war, regardless of whether the issue is actually controversial, or if it has a simple, obvious solution.

The people leading the Covid denialist movement aren't stupid. They are just cynically scoring political points with their base.

And we have studies[1] that show UV light kills the virus in less than a minute which further limits airborne spread outdoors during the day[2].

[1] https://www.cuimc.columbia.edu/news/far-uvc-light-safely-kil...

[2] Even on overcast days, as people who forgot sunscreen on cloudy days can attest too.

All of the media messaging around COVID has been a complete disaster from the moment it became apparent it was spreading in January in China. One of the main takeaways from this pandemic needs to be that doctors and experts need to learn how to say the words: "I don't know, but we are working hard to find out." Way too many people have made statements that later turned out to be false. The lack of any consistency and the complete flip-flopping on masks has completely undermined the public's willingness to trust the experts.

The messaging regarding masks was "They don't keep you from getting it, and everyone should be inside right now to avoid spreading it if they have it, so avoid buying a mask to make sure there are enough for people who need them." The messaging regarding masks now is, "They don't keep you from getting it, but they do stop you from spreading it, so since there are enough masks now for everyone, you should wear one." It doesn't seem like a flip-flop so much as responding to the current state of the world.

I think the public's willingness to trust the experts has been undermined more by a large portion of the US government deliberately trying to undermine public trust in the experts.

“When to use mask:

- If you are healthy, you only need to wear a mask if you are taking care of a person with suspected #coronavirus infection.

- Wear a mask if you are coughing or sneezing”

WHO, Mar 1, https://twitter.com/who/status/1234095938555260929?s=21

“the wide use of masks by healthy people in the community setting is not supported by current evidence and carries uncertainties and critical risks.”

WHO, Apr 6, https://apps.who.int/iris/handle/10665/331693

That second source goes on to point out that its major concern (in terms of "uncertainties and critical risks") is healthy people using medical masks in places where there isn't enough supply and depriving healthcare workers of them, like I said. It specifically does not advise against nonmedical masks, and simply notes that the WHO was still actively studying their use at the time and would make a recommendation when evidence was available.

So the "flip-flop" here was the WHO saying "I don't know, I'm looking into it," and then later saying "I've looked into it and have some strong recommendations."

This is a good article.

I work at a biotech company that studies virus transmission and helps others study it. It was clear from the very beginning that transmission was airborne. Why would it not be? That the WHO and some doctors were assuming it was not seriously damages their credibility as healthcare professionals.

Current events should lead people to seriously question deference given to doctors. They need to be held accountable for their actions and must be made to listen to professionals in other fields.

Why wasn't there a large spike with the recent protests in the participating demographic?

https://www.forbes.com/sites/tommybeer/2020/07/01/research-d...

The chants "no justice, no peace"? "I can't breath"?

Those were clear chants. Everyone breathing on each other while chanting. Unencumbered by a mask.

> Unencumbered by a mask.

Got a source on this? From the protests I've been attending, I'd say mask usage is easily at 99% of attendees. Everyone pictured in your linked article also has a mask, at least 10% have full masks and face shields.

hell at the ones I went to there were roving groups of people handing out masks and gloves (more masks than gloves and the masks came directly from the box), hand sanitizer, and water.

it was a sight to see honestly and very heartening bit of community and mutual aid.

That's only a single paper, hardly conclusive. But also:

> Unencumbered by a mask.

The picture at the beginning of the article you linked shows every protester wearing a mask.

Note that the findings don't say "those who went to the protests did not catch the virus or transmit it to others". They just say there wasn't an overall spike after the protests.

The fourth bullet point addresses this directly:

"The study’s lead author, Dhaval Dave of Bentley University, said, “In many cities, the protests actually seemed to lead to a net increase in social distancing, as more people who did not protest decided to stay off the streets.”"

Also, though it isn't part of the NBER working paper, the Forbes article mentions that:

'the Minneapolis Department of Health reported that more than 15,000 people were tested at centers set up in communities affected by the protests, and 1.7% of tests came back positive—below the statewide average of about 3.6%. According to the Washington Post, protest attendees in Minneapolis returned positivity rates of less than 1% and that “officials believe the low infection rates reflect that the protests were outside, that most people wore masks and that people spent most of their time in motion, circulating through the crowd.”'

They're in the extremely well ventilated outdoors, and at least at the protests I was at there were very few people not wearing masks. Also, people in these gatherings tend to mill about, which means any contact with a stream of virus-infused exhalations will be brief and less likely to introduce a viable quantity into you.

This is what the Forbes article reports the Washington Post saying that Minnesota health officials believe, and it seems to make sense.

I haven’t seen any research on this, but is there a chance being introduced to very small viral loads could actually improve your expected future health? We know that larger loads are harder to fight and produce worse symptoms, but what of “mico-loads”? It would seem they should almost act as a semi-vaccine: you get an easy to fight and low symptom load once, then you’ve created antibodies for the future. So long as you continue to be exposed to micro-loads in day to day life, those antibodies shouldn’t go away, and you’ll be safe from any potential “mega-load”.

I don't know if there's data specific to SARS-CoV-2, but this is the mechanism behind inoculation (as opposed to vaccination). This method was used to reduce smallpox deaths before vaccination had been developed.

To the other folks replying: I looked up the protests on ddg images, and about half of the protesters in those photos were wearing masks.

https://duckduckgo.com/?q=blm+protest+2020&iar=images&iax=im...

The plural of anecdote is not data. There were obviously a mix of behaviors, and which was predominant and where is a crucial factor to control in any analysis.

You can't simply search for "BLM Protest". The 2020 protests are not the first BLM protests, these are just the first BLM protests that are getting global attention.

On the first row of images that appear for me, when following the sourced article, they are from the years:

2015, 2016, 2015, 2016, 2017, 2020 (everyone in this picture has masks)

Yeah, I noticed and fixed the search.

> Unencumbered by a mask.

That hasn’t been my experience. Every action I’ve attended has had clear messaging leading up to it about masks and social distancing, and attendees have adhered to guidelines.

This is adhering to the social distancing guidelines? https://nymag.com/intelligencer/article/george-floyd-protest...

The crowds are tight and packed.

That was my experience in June. Crowds were packed but nearly everyone had a mask. It makes me think the masks are more important than social distancing (at least outdoors), but I'm not gonna stop social distancing where feasible. I was very pleasantly surprised that people didn't get sick.

You started with masks, not social distancing, so sticking to your original argument, I'd say that link you provided just indicates that masks worked well enough to protect the protestors, even without considering the social distancing aspect.

'social distancing' was a response to the parent.

You're arguing for how effective masks are in stopping this virus. A fact that it'd be nice if more people accepted. And is great info that the protests demonstrated so.

The protestors are in the age demographic that are by far least affected by the virus.

“We estimate that susceptibility to infection in individuals under 20 years of age is approximately half that of adults aged over 20 years, and that clinical symptoms manifest in 21% (95% credible interval: 12–31%) of infections in 10- to 19-year-olds”

https://www.nature.com/articles/s41591-020-0962-9

https://www.cdc.gov/nchs/nvss/vsrr/covid_weekly/index.htm#Ag...

Were you going to address the comments regarding your statement that people aren't wearing masks or are you just going to ignore them and try to find something else to reinforce your narrative about the 'participating demographic'?

People scream at the cops, without masks. The same for chanting. You can either muffle yourself, or lower the mask and project loudly.

With a few hours of intense marching, people naturally want to remove/adjust/lower the mask to talk/shout/run. Even with those wearing their masks, their effectiveness won't be 100%.

Which leads back to the OP's point - if the virus is airborne, why don't we see an uptick in deaths for that demographic?

Because the 'participating demographic' skews young.

https://www.nature.com/articles/s41591-020-0962-9 https://www.cdc.gov/nchs/nvss/vsrr/covid_weekly/index.htm#Ag...

The paper the Forbes article references doesn't seem to refute the idea that there wasn't a spike in "the participating demographic". They mostly focused on the increase in social distancing among those not participating in the protests.

That aside, the Atlantic article talks about outside air diluting the virus. The Forbes article you linked also talks about this.

I think a key part is also the dose in which you get infected that leads to illness. When you're in the open air, breathing and chanting, the dose of the virus is so low, that the immune system can easily defend against it.

Also, the virus doesn't kill most people, the human immune (over)reaction does. This is my laymen's way of describing a (deadly) course of the virus and disease.

1.1. person breaths in microparticles (aerosols) contaminated with the virus 1.2. breaths in low or high dose (in further steps shown as L and H) 1.3. (L and H) directly deep into the lungs [1] (almost like intracellular viral infection)

2.1. (L and H) innate arm of immune system tries to combat it 2.2. (L and H) adaptive arm of immune system is being activated [2] (takes at most 7 days to mount a significant response) 2.3. (L) virus replicates slowly and is kept in check, because low dose is easier to combat by innate arm of immune system (availability of Vitamine D seems key as it exhibits direct antiviral activities [3] probably Zinc as well as it inhibits RNA replication of the virus [4]) 2.4. (H) virus replicates fast because the high dose can't be handled by the innate arm -> This is the point when most people will either get more ill and be hospitalized, or recover. This is also when it's too late for HCQ and Zinc to be effective. (Set of studies showing effectiveness for early or late treatment with HCQ + Zinc + Azithromycin[5]) 3.1. (L) virus is controlled and the innate arm of the immune system can handle the virus. The adaptive arm cleans up the last bits of the virus and person is no longer ill. -> Low dose infected person might stay Asymptomatic or experience a Light Cold or minor fever. 3.2. (H) virus is out of control and the adaptive arm reacts with an overreaction of the antibodies resulting in a cytokine storm 3.3. Person gets severe inflammation and thrombosis and gets heavily ill. -> High dose infection: this is the point of no return and anyone who reaches this is bound to have a long track of recovery in front of them, or death.

I've added some sources, be aware that for each source there's multitude of other sources claiming the same thing. Research yourself!

[1]: https://www.intechopen.com/books/rhinosinusitis/aerosol-part... [2]: https://en.wikipedia.org/wiki/Adaptive_immune_system#Functio... [3]: https://youtu.be/Mdc7T2UTHBI?t=216 [4]: https://youtu.be/WZq-K1wpur8?t=447 [5]: https://c19study.com/

Regarding [5], where is the disagreement on the effectiveness of HCQ + Zinc + Azithromycin?

Overwhelmingly the news has been negative.

The above doesn’t appear to include all of the research.

It does include everything. It's the narrative that comes from the few negative results, as well as the big Lancet article that was retracted that got the news very negative.

But if you know of missing studies please add them.

The disagreement of effectiveness is mostly about it being used in a late stage of the disease (as mentioned), not in early stage.

I have several (medical) doctors in my family. They were pretty clear from the beginning that what the WHO was saying was BS. They pretty much agreed with what you're relating; I don't think it's doctors in general who are ignorant of how a virus gets transmitted.

I completely agree with your first point; but what we need to seriously question is the cherry-picking of sources that were paraded in front of us by the media.

YouTube took it upon themselves to ban any videos that contradicted the WHO statements.

Don't you love it when people force their opinons on you, 'for your own good'?

All professionals and experts should be held accountable for their actions: doctors are no exception. The issue with "needing to be held accountable" is that you're calling doctors a monolithic group and implying that they aren't already heavily screened and scrutinized.

Doctors are, and should be, some of the most elite minds and highly respected scientists/caregivers. Like any group, they have inter-group controversy and debate, but let's not use that to pile onto the anti-science, anti-vax, anti-medical chorus which is gaining steam on the internet. Some doctors get things wrong: most doctors, however, enact evidence-based practices which have been vetted by statisticians, chemists, and physicists who help innovate and inform medical decision-making.

As high-minded as our concerns about doctors being incorrect might be, let's keep a wide view here and not tear down a vast-majority noble and expert profession. Let's have a nuanced discussion where we admit doctors are both experts, highly select, but also people with flaws too.

Apply that to cops and people would say you're off your rocker. Self-policing doesn't seem to work. We need something more.

Practically there is no way to hold a doctor accountable. There's various laws to limit liability and in most courts in the US you'll need another doctor to testify against your doctor. As the number of doctors is low they tend to know each other at least in passing, and it's hard to actually enforce professional standards.

What matters the most are practicing doctors, not doctors involved in research. I forget what the numbers are, but there are still more GPs and specialist than there are researching practitioners.

If you venture far outside a big city the quality of healthcare experiences a precipitous drop. It's terrifying. Even within a big city like New York, we found out that the ER/ICU professionals were killing people with ventilators! Why didn't they just supply oxygen instead, like they seem to be doing now?

>> Doctors are, and should be, some of the most elite minds and highly respected scientists/caregivers.

Hyperbolic sycophantry like the above only exaserbates the ego and credentialism problems which already plague the medical profession. Respect is earned.

> It was clear from the very beginning that transmission was airborne.

To me the only thing that was clear was the definition of airborne is not standard.

By strict definition, COVID is not airborne since it seems to require a host material (e.g. water droplet). This is in contrast to measles which individual virus particles can survive without a host material. Practically speaking though, COVID seems to be able to survive well in such small droplets that it acts like an airborne disease.

At a public health, COVID might as well be treated as airborne. Within acute care settings, this is a critical difference is being used as justification that a _properly_ fitted N95 and eye covering is sufficient to care for COVID patients. If COVID was truly airborne, all patient care should require airborne-level PPE (like PAPRs).

Just to be pedantic. SARS-CoV-2 is the virus, Covid is the disease. The same as HIV vs AIDS.

I'm aware. Covid is half as long and everyone knows what I'm talking about.

HIV/AIDS is a bit more important because the disease can lag the infection by a large period.

>By strict definition, COVID is not airborne since it seems to require a host material (e.g. water droplet).

You are wrong. Read:

1. https://www.who.int/news-room/commentaries/detail/transmissi....

2. https://www.nature.com/articles/s41586-020-2342-5_reference.....

Aerosol transmission is the main vector.

Consider posing your statement in the reverse: SARS-CoV-2 does not disperse in droplets, and/or is not infectious when not in a droplet. There is no reason to believe either of those things!

It's totally reasonable to assume the virus could separate from a droplet and would remain infectious by itself for enough time to infect someone. This is common in other viruses, and seems to make sense from first principles. Why would virus particles not be able to form aerosols?

In the first article you posted it reads:

> To date, transmission of SARS-CoV-2 by this type of aerosol route has not been demonstrated; much more research is needed given the possible implications of such route of transmission.

That seems to be in direct opposition to your statement, correct? Or am I missing something.

Well, I forgot the WHO still does not think aerosol transmission is likely. But they do have a section on airborne spread that exceeds most people's expectations.

The thing is -- why assume it can't form aerosols and that those aerosols aren't infectious? By demanding evidence for aerosol formation that is what they are stating. It makes no sense. Most viruses do form aerosols, and those aerosols do seem to be infectious.

So I read those, and at least according to the WHO document, it seems to be the case that while viral RNA is detectable in a non-aersolized state in the air, they haven't been able to find any cases of this causing infection (See section labelled "Airborne transmission").

Are you really prepared to make the bet that they aren't infectious?

> Most viruses do form aerosols, and those aerosols do seem to be infectious.

It's my understanding that most don't spread in this fashion. If you're hospitalized with cold/flu, your care team will observe droplet precautions, not aerosol ones.

If you have measles, which spreads via aerosol, they'll be using substantially more gear. The aerosol transmission is also why measles is shockingly easy to spread versus most other diseases.

> If you're hospitalized with cold/flu, your care team will observe droplet precautions, not aerosol ones.

From my understanding, part of this is because most hospitals don't have aerosol specific precautions. Pre-COVID, anything requiring more than droplet precautions was simply handled with full-airborne precautions (negative pressure room, PAPR, etc).

Ideally, we'd have the airborne-precaution PPE for all COVID care but that's extremely expensive and leadership (hospital and gov't) have become aware that healthcare workers will still show up to work even without proper protection.

This is my point but people keep downvoting it. "That's expensive, so that can't be true."

From WHO:

>The physics of exhaled air and flow physics have generated hypotheses about possible mechanisms of SARS-CoV-2 transmission through aerosols.(13-16) These theories suggest that 1) a number of respiratory droplets generate microscopic aerosols (<5 µm) by evaporating, and 2) normal breathing and talking results in exhaled aerosols. Thus, a susceptible person could inhale aerosols, and could become infected if the aerosols contain the virus in sufficient quantity to cause infection within the recipient. However, the proportion of exhaled droplet nuclei or of respiratory droplets that evaporate to generate aerosols, and the infectious dose of viable SARS-CoV-2 required to cause infection in another person are not known, but it has been studied for other respiratory viruses.(17)

What the WHO and some doctors are doing is going: "despite the fact that it seems like it can spread via aerosols and that seems fairly likely, we want hard proof and are willing to risk our lives on that basis."

So, lol.

> Aerosol transmission is the main vector.

Yeah. And that's not 'airborne'.

> Aerosol transmission is the main vector.

By strict definition, aerosol is not airborne. The behaviors converge, but there is a technical difference. It's particularly important when it comes to designing effective filtering material and sanitization processes.

Err.. what? Very fine particles are also included in aerosols. The definition I'm aware of is mostly based around whether there is an appreciable settling time.

Wow, what a good article. Finally an article in a well respected publication that goes over the science of the Covid19 transmission, and appears to be non-partisan as well (what a tragedy that the approach to combat the disease has become a partisan issue). I really hope this article will, dare I say, "become viral". If it does, this article by itself could help save tens or hundreds of thousands of lives.

But it won't. The reason things became "partisan" is precisely because things like the article are useless and ineffective. You're assuming a shared reality that doesn't exist.

You could be a little more gracious, and write a bit about the counterargument in your head, rather than framing your opinion as a dismissive argument right away.

Edit: There may be some confusion: When you say, "things like the article are useless and ineffective", are you saying it's useless in reducing infection, or useless in communicating the message of how to reduce infection?

I can only assume you're being downvoted because you've confused the chicken and the egg.

Partisan issues don't exist because articles like this are useless and ineffective. Partisan stances on this sort of thing is what makes people believe articles like this are useless. You have it backwards.

I would absolutely agree, though, that there is no such thing as a cultural 'shared reality' anymore. That is the base of the problem. There are very, very few shared experiences, and a section of the population is not, seemingly, even interested in trying to understand someone else's viewpoint.

Not sure what GP's line of reasoning is, but I agree the point could be stated in a finer way, although I roughly agree with it.

> Partisan issues don't exist because articles like this are useless and ineffective. Partisan stances on this sort of thing is what makes people believe articles like this are useless. You have it backwards.

I don't know. Is it really backwards? I can see how it could be argued that partisan stances spread as a consequence of people having short attention spans and preferring short, context-less flamewars on twitter or other social media instead of reading long-form articles like this one and developing their own thoughts on issues.

Therefore it could be argued that, since people didn't pay (much) attention to articles like this to begin with, "they are useless and ineffective".

It might actually be a self-reinforcing situation, though...

But the whole point of the chicken and the egg problem is that it is not apparent which came first.

Yes, I think an analogy about a cart and horse was instead called for.

We seem to agree 100%. The GP expressed hope that better information (such as this article) will be able to change people's minds and alter the course of the pandemic. I find that pretty naive. The reason the pandemic took the turn it did is precisely because research, reasoning, expertise, etc is incompatible with the existing cultural divides in the US. Why would more of the same produce a different result?

I am still shocked: months after research has shown that SARS-CoV-2 is airborne stable in aerosol form for over 3 hours, we still aren’t telling the public that room air purifiers are a ‘good thing’ (for making indoor air like outdoor air - in regards to virion density per cubic air volume)

The filter technology is essentially the same as in the N95, orders of magnitude more effective than cloth masks.

Put these indoors, multiple per classroom/working space to help the air refresh in sub 5 minute intervals.

My wife works in a doctors office which has stayed open through the pandemic. She sees a few people a day in a small room. The very first thing she did after the pandemic hit the US, was buy an air purifier and she runs it continually. I'm quite surprised that they aren't more common in medical offices in general. The benefits of the air filter are cumulative with other protections—particles caught by the filter can't bypass the mask.

Filters should be mandatory in any enclosed room, the fact that they don't even talk about them as part of the discussion about schools and businesses opening is mind boggling to me.

Expect we will see a repeat of the bungled rush for air purifiers as we did with ventilators.

As with the ventilators, a bungled rush for them is better than not using them at all. Obviously if they had a more ordered distribution it would be better, but any movement in the correct direction would be an improvement.

Here would could at least prioritize schools? Ventilators was only bungled because it turned out to be the wrong therapy... air purifiers is a win win win

> Here would could at least prioritize schools?

Or just mandate them in schools and let the rest of the population figure it out. Though even this would be fraught, there aren't enough air purifiers on store shelves to adequately provide for public schools.

Added benefit: post-covid pandemic, improved indoor air quality with all the included benefits!

Air quality associated with:

Alzheimers: https://www.scientificamerican.com/article/the-new-alzheimer...

Cancers, plural: https://www.aacr.org/patients-caregivers/progress-against-ca...

Sperm Quality: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4443398/#sec995...

Female Fertility: https://www.newscientist.com/article/2207560-exposure-to-air...

Autism: https://www.sciencealert.com/particulate-matter-in-air-pollu...

Bipolar/Depression: https://www.nationalgeographic.com/environment/2019/08/air-p...

side note: please make the ICE>Electric transition happen faster... sigh

Thanks for these links. I've saved them for future reference!

Sperm Quality? That's it - the window stays open!

A thing I really wish would catch on is people actually leaving their windows open to get proper ventilation of their living spaces.

Air purifiers seems like a great idea, but if the outside is the safest place in terms of the virus, bringing the outside in to you seems like a no-brainer.

In general, I'd say outdoor air beats indoor air probably 99 times out of 100.

It is all about virion particles per cubic meter (similar to how they classify class ## cleanrooms for the semiconductor, but in that case they talk about dust particles).

Outdoor air works through dilution (‘the solution to pollution is dilution’ is the phrase often used).

Indoor air being purified is often much cleaner than outdoor air (assuming CO2 levels are not of any concern), this is especially true during wildfire season.

If you purchase a PM2.5 sensor and put it in your kitchen while you make toast, you will be shocked. (do this with and without an air purifier near by to be calmed :))

> this is especially true during wildfire season

Curious what if any effect that would have over here in Iowa. I would guess negligible, but we do get high-level haze occasionally when there are wildfires in Canada.

> If you purchase a PM2.5 sensor

I have been curious about these in the past. Do you have any recommendations? I couldn't find enough info to feel comfortable that whatever I bought might actually tell me useful things.

> Indoor air being purified is often much cleaner than outdoor air

As a more or less believer in the Hygiene Hypothesis [1], I'm not convinced that this is a good thing. But I guess also most people don't have purified air in their homes so purified stale air is probably better than just regular stale air.

[1] https://en.wikipedia.org/wiki/Hygiene_hypothesis

Ideally people would be outside more if the air is good. When they have to be indoors, it is better to purify so we aren’t being exposed to ‘unnatural’ environments, i.e. lots of skin flakes floating around with dust mites, etc.

Also, many people in South America have shortened lives because they are indoors with wood burning stoves that are giving them lung cancer.

This is a good quality particle counter for a home or school:

https://www.amazon.com/Dylos-Laser-Particle-Counter-DC1100/d...

It can be connected to a computer to record particle counts long term using the included Windows software. Useful for seeing that your Hepa air purifier is actually working. There are many brands of hand held instruments for use with HVAC systems. Their cost ranges from $100 on eBay up to several thousand dollars for high end instruments that can measure many particles sizes. They generally are not meant to be left on to take measurements over days though. There are also professional weather instruments that use a laser to count particles in the air outdoors.

Opening the windows more often may also help a lot. This is a very simple method to reduce risk of spreading. It is free and especially useful for places like schools. But I do not think I read about this in mainstream media. It's all about masks and social distancing.

I am concerned about winter, because we have to prep now for that.

On the northern hemisphere we still have a few months (actually, two or three only). That's why the article is correct, we urgently need to talk about airborne transmission.

I've been saying this from the start - should be mandated in public transport.

> "...SARS-CoV-2 is airborne stable in aerosol form for over 3 hours..."

see, this is the kind of insinuation that does none of us any good. it's like doing PCR to connote live virus particles live for 17 days on surfaces (spoiler: they don't).

with that said, i'm down for air purifiers in living spaces† for a whole host of good health reasons, but most commercial spaces and public buildings (like schools) already have HVAC systems incorporating HEPA filters (as good or better than N95 masks). whether the operators change the filters on an appropriate schedule is a different matter however. residential HVAC systems, at least in newer construction, also tend to have HEPA filters (but not always).

† i have a blue pure 211+ for my apartment: https://www.blueair.com/us/air-purifiers/blue-pure-211-plus/...

If you are in the USA, I don't believe your claim that most commercial or schools have HEPA in their air filtration system, and know it isn't true for new residential in the PNW.

The school I attended as a child didn't have any filtration at all, for example.

there's certainly variation, regional, by quality level, as well as generational. class A commercial will almost certainly have filtered hvac, for example. my 1930's vintage high school most certainly didn't.

Filtered, yes, but not HEPA.

> most commercial spaces and public buildings (like schools) already have HVAC systems incorporating HEPA filters (as good or better than N95 masks).

So, here's some anecdata. I have a PM2.5 sensor; not a great one, but good enough to measure relative changes. After buying an air purifier the PM2.5 count in our house dropped dramatically and consistently. Whereas the lower end before was a "2", now it reaches to "0"; I'd never seen the sensor register 0 before this. And the spikes from cooking are quickly scrubbed, whereas before they would cause a lingering increase in PM2.5 for the rest of the night.

Even though I spend extra to get the higher grade filters for our HVAC, an air purifier still seems to have objectively improved the air quality far beyond what our HVAC was doing.

In other words, I'm not sure an HVAC is a good replacement.

This, it is amazing how long small particles linger. It’s like looking in a sun beam and seeing floating fibers near the couch.

A very fun experiment to show children is to use a green laser pointer near a carpet floor so it is floating across the floor a couple inches.

Then have the children hit the carpet around the beam and the beam will suddenly appear as the light scatters from the micron-sized dust particles. You can see how long it takes them to resettle, and point the laser anywhere to count a crude interaction/second with the light beam to get a sense of how dirty the air is (laser light volume is quite small :))

that could be, but i'd note that a 2->0 PM2.5 count drop is likely not material to health as opposed to, say, a 20->2 drop. and furthermore, the time-averaged PM2.5 count while home is more relevant than the minimum absolute value.

> is airborne stable in aerosol form

AKA, it's not airborne. If it requires water particles to host the virus, its not airborne.

We need good diagrams that show the virus in a small drop of water with labels showing what we mean :)

If they can't put these everywhere they should at least target the minority's in our country who are most susceptible; specifically, people over the age of 75.

> we still aren’t telling the public that room air purifiers are a ‘good thing’ (for making indoor air like outdoor air - in regards to virion density per cubic air volume)

> The filter technology is essentially the same as in the N95

So, due to the very small size of this virus, in microns. Most air filters on the market are still not good enough. HEPA isn't good enough, is it better than nothing? Yes but not much. A MERV 14 isn't good enough. I've seen some promising UV light tech but...AC units are pretty ill equipped for this virus.

I'm even curious if studies have been done in hospitals have the equipped AC filtering system to stop this virus. Air flow and filtration is a tradeoff currently. Try to blow out a candle with an N95 mask. It's extremely difficult. The filter technology is not the same.

> orders of magnitude more effective than cloth masks

Cloth masks help about 40% reduction, surgical masks 80%, and N95...95%. I find it very annoying that governments are encouraging cloth masks because they could be use their size and buy surgical masks for everyone at a very cheap cost (economies of scale).

Also, the creator of N95 masks got out of retirement and found that if hospital workers had 7 masks, one for each day. Just rotating them in the storage closet is very effective to reusing them without contamination.

The virions initially travel in large droplets of water that eventually turn into small micron-sized water droplets, these happen to overlap with the high filter efficiency regime.

For aerosol filtration, cloth masks are not very effective, much less than 40% has been measured.

You can also get air purifiers that run the air past a UVC lamp to kill viruses:

https://www.amazon.com/gp/product/B01JKDAN2M

Does anyone know how effective home filter purifiers are? I have been going to my office because of AC.

I am about 20 feet from my partner. He keeps his door closed I keep mine open. I bought two purifiers/filters one for each. they say HEPA but I have no idea if that's true. I keep mine running all the time even overnight. I'm young and healthy so likely risk is low but still being hot might be a worthy trade off.

One commenter below says HEPA isn't even effective

When I look at this heat map of recent cases per capita in the US

https://globalepidemics.org/key-metrics-for-covid-suppressio...

the first thing I see is hot spots all across the southeast and desert southwest. These places have widely varying governments and cultures, but the one thing they do have in common right now is: they're hot.

My suspicion is that many of the outbreaks we've seen recently are caused by people from different households congregating indoors in buildings with air conditioning and closed windows. The article mentions this, but I rarely here it talked about on the news:

"The importance of aerosols may even help explain why the disease is now exploding in the southern United States, where people often go into air-conditioned spaces to avoid the sweltering heat."

And this might switch in winter, as people in the south get outside more and the north buttons up for the cold.

This is something I currently speculate too. Hotter states really benefited from AC allowing people to live there comfortably. I think it might show us what’s coming as people move indoors in colder months elsewhere.

It’s getting harder and harder to stay away from people from a purely psychological standpoint, and I think fall is going to get bad in the PNW as people congregate indoors to stay out of the wet and cold.

Ben Shapiro has been saying that for months..

My company took steps to address this months ago. The re-circulation rate was set to zero so all air is fresh make up air from outside. This has significantly increased our cooling bill since it's summer, but it was something that we felt important even though there hasn't been much science to back it up. We also have a UV system hooked up to our system, but this has been installed for the last 2-3 years now.

I wonder if air-to-air heat exchangers could address that cost issue.

Surely all industrial / professional HVAC get installed with HRV and the loss here is going from the "100% efficient" recirc to HRV, no?

Not all if it isn't designed that way (ours isn't because we never plan to not use recirc). The loss isn't actually that much and since we are using low temp cooling water to cool the air and we have a significant amount of that on site already we barely notice (still a cost though).

How old is your building? New construction is so weather sealed and lacks fresh air leaks to meet air quality standards. Pretty sure whatever standard to get a green rating on a building requires outside air to be mixed in and due to efficiency requirements there has to be heat exchanger.

25 years...but we also have the ability to open outside dampers on our return air chases to output all air if needed.

Energy Recovery Ventilation (ERV)

https://en.wikipedia.org/wiki/Energy_recovery_ventilation

Yes. I was wondering if the wheel-based ones had some means of killing pathogens on the wheel, rather than transfering them back to the incoming air stream.

I've been thinking about getting two CPU cooling fans that have the heat sink at a distance from the fan and use a heat pipe to move the heat over to the fan and connecting them back-to-back so one fan blows outward and one blows inward. Something like two of these:

http://i.ebayimg.com/images/i/151452729196-0-1/s-l1000.jpg https://prod.scorptec.com.au/10/299/65429/121859_large.jpg https://brain-images-ssl.cdn.dixons.com/7/2/10178327/l_10178...

That way outgoing air would warm (or cool) the incoming air. If a Hepa filter could be added to the incoming air fan it would make an ideal unit to put in the window at fairly low cost. Since they are CPU coolers they could probably be made speed adjustable also.

That would transfer sensible heat, but not latent heat.

Countercurrent exchange is the way to go with a scheme like this, so you'd want a series of pipes at varying temperature.

How does that work? Is it just a setting on industrial HVAC systems or did it require someone coming out and reconfiguring things? I’ve heard some schools are considering leaving the windows open year-round while running the heat/AC to get air turnover. Maybe because those HVAC systems are dated?

Most big HVAC systems have this ability. On a rooftop unit usually it's as simple as a hatch that you slide; a split system would have to have a separate fresh air duct you can control with a damper. Newer systems typically have explicit fresh air makeup systems with heat exchangers.

Most schools with forced air ventilation should already have such a capability, if they bothered to look. If not, if would certainly be cheaper to have one installed than to leave the windows open. But of course, it may be easier to do one than the other bureaucratically.

> Most big HVAC systems have this ability.

This is patently untrue.

It's an industrial HVAC system that has control systems to allow this (simply just changing damper settings)...but ours is also ~25 years old. Schools opening windows would just be a low tech way of looking at how we change the damper settings.

One issue is that we seem to have an all-or-nothing view of infection. People think that either a virus gets in your nose and you get sick, or it doesn't and you're fine. This extends to thinking that either there is a risk or there isn't, which motivates incorrect anti-mask arguments.

In reality, the probability of infection varies continuously with the degree of exposure, and the minimal infective dose might be prevented even if not all viral particles can be blocked.

https://en.wikipedia.org/wiki/Minimal_infective_dose

With airborne transmission, it is practically impossible to reduce the transmission probability to zero in many situations, and we have overlooked the value of finite improvements. However, the circumstantial evidence suggests that, since super-spreader events are correlated with apparently high airborne concentrations of viral particles, that reducing the duration and intensity of exposure may yield significant benefits even if inhaled air cannot be made completely free of virions.

Exactly, that "all or nothing" is the main problem in in how most of the people think about the whole topic.

I've read one work that gave the very simple estimates: if the infected person wears the surgical mask it will emit 50% less in the air, and if the non-infected person wears the surgical mask that person will get 60% of what's in the air. But combined, that means that the non-infected person will get around only 30% of what it would get when nobody would wear a mask. Which seems to be way too little for personal "full" protection, but looking more globally:

If the R factor (reproduction number) is 2.7 with no measures, and if everybody wears a mask and other limitations are respected (physical distancing, limiting the number or people in the closed spaces, ventilation, etc.), all together it can result in the R factor being reduced to less than 1: With the known no-measures factor 2.7 we have exponential growth. With the factor under 1, we have a steady decay in the number of infected people.

There we also "just" have to reduce that factor to 30% of the no-measures one. It's not so easy as some people spread to many, and a lot already don't pass the virus to others. That's why groups of people near each other change everything too much.

But just by maintaining the factor under 1 (the lower the better) we guarantee that the relative number of infected around us will be always be smaller and smaller, and that's can be more than enough for the population as the whole.

That's why wearing the masks and any additional good measures together do help, even if every measure, evaluated alone, for only one person, "doesn't protect" enough.

So it is not just either 0 or 100%, but everything in between: not everybody has to use the same protection that the medical workers have to to improve the chances for everybody. But everybody should do it. One person who's actually infected and not wearing its mask changes the number of viruses passed to anybody in its vicinity from 30% to 60%, when all the rest wear the masks, or to 0 to somebody who's also not wearing the mask. From the starting 50% and 60% of masks "working" we get all the other outcomes too.

And the same is valid for testing. Rapid wide scale cheap testing to identify who should enter the building doesn't have to be as good as PCR tests to still give us immense benefits, if we have it and use it. We just have to be clear that we want it, and that we know now it's not about "either 0 or 100%."

Also, the pictures (and the video) explaining much more than many words:

"Face coverings and mask to minimise droplet dispersion and aerosolisation: a video case study"

https://thorax.bmj.com/content/early/2020/07/24/thoraxjnl-20...

Short-distance aerosol transmission changes things a bit:

* Social distancing isn't enough to guarantee safety in indoors spaces: bad news for bars, clubs, gyms, concerts, and restaurants

* Outdoors spaces are probably safer than we previously thought

* Indoor mask-wearing becomes CRITICAL in public spaces

* Indoor ventilation becomes extra important, using fresh air from outside or filtered/UV-sanitized air

* Indoor air purifiers with HEPA ratings or UV sterilizer features may become valuable

But the same overall guidance still applies: avoid crowds, wear a mask, keep your distance, outdoors activities are safer than indoors activities

> Indoor mask-wearing becomes CRITICAL in public spaces

Mask wearing provides minimal benefits against droplet transmission, but they do nothing at all for small droplet aerosol transmission.

What do you consider a small droplet? The masks are tested with 0.3 micron droplets. Do you have a source?

Studies have found that a combination of multi-layered cotton and chiffon/silk masks prevents intake of both large and small droplets. Silk/chiffon act magnetically on smaller particles to keep you from breathing them in, while the thick cotton layers stop large droplets. The aggregate effect is similar to N95, but more washable and reusable. It blows my mind that this was discovered a couple months ago and the government still hasn’t funded the mass production of such masks. After I read the study, I bought 2 masks on Etsy.com: a multilayered cotton mask and a silk mask. I wear both when I go out. What’s great is that I don’t just protect others from me, but I also protect myself from others to a large extent (as opposed to just wearing the cotton mask). As for comfort, silk is light and thin, so it doesn’t add any noticeable discomfort on top of the cotton mask.

https://news.uchicago.edu/story/homemade-masks-made-silk-and...

Note: Newer studies have found that even just a thick cotton mask does somewhat protect you (not as much as cotton + silk of course, but they protect others from you quite effectively). You still need to be careful, generally avoid indoor environments with strangers, and socially distance. Not that that disclaimer is super necessary, because other studies have found that masks do not make people behave more recklessly :) If anything, they make you more careful and acutely aware of COVID risks.

> Newer studies have found that even just a thick cotton mask does somewhat protect you

No they haven't. If the effect of masks was so strong it would be easy to find that when we do trials. We've done the trials and we struggle to see the effect. Once we drop down the quality requirements we start to see an effect, but even that is mild.

https://www.thelancet.com/action/showPdf?pii=S0140-6736%2820...

> Although direct evidence is limited, the optimum use of face masks, in particular N95 or similar respirators in health-care settings and 12–16-layer cotton or surgical masks in the community, could depend on contextual factors; action is needed at all levels to address the paucity of better evidence. Eye protection might provide additional benefits. Globally collaborative and well conducted studies, including randomised trials, of different personal protective strategies are needed regardless of the challenges, but this systematic appraisal of currently best available evidence could be considered to inform interim guidance

There's no way to spin phrases like "direct evidence is limited" and "paucity of evidence" to mean "we've got good quality evidence that shows an effect".

That's actually the opposite of what the evidence shows. Masks - even crappy ones, with poor mask protocol - dramatically cut infections https://arstechnica.com/science/2020/06/modeling-the-impact-...

Citation: https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818

Remember: even if a mask doesn't effectively filter out very small particles, it still restricts the velocity of air passing through it. This means aerosolized particles will not travel as far.

About your arstechnica link: if masks don't work all that effectively you need huge numbers of people to wear them to prevent a single infection.

https://www.fhi.no/globalassets/dokumenterfiler/rapporter/20...

> Non-medical facemasks include a variety of products. There is no reliable evidence of the effectiveness of non-medical facemasks in community settings. There is likely to be substantial variation in effectiveness between products. However, there is only limited evidence from laboratory studies of potential differences in effectiveness when different products are used in the community.

> Given the low prevalence of COVID-19 currently, even if facemasks are assumed to be effective, the difference in infection rates between using facemasks and not using facemasks would be small.Assuming that 20% of people infectious with SARS-CoV-2 do not have symptoms,and assuming a risk reduction of 40% for wearing facemask, 200000 people would need to wear facemasks to prevent one new infection per week in the current epide-miological situation.

Here's all the science: we don't know if masks work or not. https://www.cebm.net/covid-19/masking-lack-of-evidence-with-...

They have a plausible mechanism of action, but they also have plausible mechanisms of harm. The above link includes one trial where they appeared to be harmful:

> It is debatable whether any of these results could be applied to the transmission of SARs-CoV-2. Only one randomised trial (n=569) included cloth masks. This trial found ILI rates were 13 times higher in Vietnamese hospital workers allocated to cloth masks compared to medical/surgical masks, RR 13.25, (95%CI 1.74 to 100.97) and over three times higher when compared to no masks,* RR 3.49 (95%CI 1.00 to 12.17). 4

This is potentially because the masks start to lose effectiveness as soon as you put them on. DIY cloth masks soon become waterlogged with condensation, and then when you breath you push out aerosolised drops.

https://www.ijic.info/article/view/10788

> This study was conducted to check the efficacy of face masks in limiting bacterial dispersal when worn continuously in Operation Theater. A comparison was done to find out difference between fabric and two ply disposable masks. The first sample was collected prior to wearing the mask, using cough plate method holding a blood agar plate approximately 10 -12 centimeters away from the mouth. the personnel were asked to produce “ahh” phonation. Participants were then asked to don the face mask, continue routine work and report to the study center located inside the theater for further sample collections at designated intervals of 30, 60, 90, 120 and 150 minutes after wearing the fabric mask made of cotton. the study was replicated on immediate next day using two ply disposable mask keeping all the other conditions and personnel exactly the same. Bacterial counts before wearing the mask were 5.36±4.38 and 5.7±2.99 on day 1 and day 2 of study. Bacterial counts were 0.96±1.06 (P<0.001) and 0.7±0.87 (P<0.001) at 30 min; 2.33±1.42 (P<0.001) and 2.36±1.03 (P<0.001) at 60 min; 3.23±1.54 (P=0.007) and 4.16±1.78 (P=0.011) at 90 min; 5.63±4.02 (P=0.67) and 4.9±1.98 (P=0.161) at 120 min and 7.03±4.45 (P=0.019) and 5.6±2.21 (P=0.951) at 150min respectively for fabric and two ply disposable mask. Counts were near pre-wear level in about two hours irrespective of the type of mask. There was no significant difference between cotton fabric and two ply disposable masks. Face masks significantly decreased bacterial dispersal initially but became almost ineffective after two hours of use.

My point is that we don't have the evidence to say whether masks work or not. You posting links to arstechnica and un-peer-reviewed pre-prints supports my point, doesn't it? If we had a Cochrane Collaboration meta analysis saying masks worked everyone would be posting that.

> There is no reliable evidence of the effectiveness of non-medical facemasks in community settings.

There has been only very limited study of non-medical (cloth) masks so far, because there was not a prior crisis that NEEDED them (where surgical mask supplies were insufficient). The fundamental problem with most of your points is that lack of research on effectiveness is NOT the same thing as proof of ineffectiveness.

We can assume that most cloth masks are probably not AS effective as surgical masks or N95 masks (although some materials can achieve surprisingly good filtration), but that's not the same thing as saying they're useless either. Especially true for models with good fit and the ability to install filters. But even a modest reduction in R-effective can greatly reduce the number of number of people infected over time.

The healthaffairs article shows that mask mandates reduced transmission: https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818

Beyond that, I'm not going to waste time going point by point in debate with someone determined to "disprove" guidance from the best available medical authorities.

More emphasis on better masks that actually might prevent aerosol transmission and less emphasis on 6 foot distancing because such things matter little under aerosol conditions where air flow patterns dominate transmission. Also much more emphasis on outdoor vs indoor activities. So no it is not really the same guidance.

Your claims do not reflect what the article and the evidence it cites show. To quote:

> Cowling told me that it’s better to call these “short-range aerosols,” as that communicates the nature of the threat more accurately: Most of these particles are concentrated around the infected person, but, under the right circumstances, they can accumulate and get around.

This is the precise opposite of your claim that 6 foot distancing would "matter little under aerosol conditions where air flow patterns dominate transmission." AT NO POINT does the article indicate that droplets are irrelevant. We know they are the key factor in person-to-person transmission. But we also now have evidence that short-range aerosols also play a role, especially in superspreading events.

The evidence is VERY clear that risks are highest in close proximity to infected individuals.

I would encourage you to take another look at the article and read closely.

Well first of all there is little evidence on both sides of the argument here. There isn't much evidence in favor of aerosol transmission and there isn't much evidence against it either. I would hope that more research can be done on this matter.

Perhaps I worded my statement poorly. Let me try to be more precise about the idea I was trying to express. If COVID really is more aerosol infectious than we have been assuming then the 6 foot distancing would matter much less in comparison because if a cloud of infectious COVID droplets is whirling in the air currents that effect will tend to dominate in the sense that your exact location relative to the COVID+ source is no longer a direct causal factor. Yes of course being farther away makes it less likely that you will be in the path of a relatively short range aerosol cloud but the important thing in that circumstance is not to be in its path and just being farther away in the same room may not be enough to avoid it.

I don't deny that if someone with COVID coughs directly in your face which apparently was considered the dominant transmission vector at first you are also likely to be infected especially if you are not fully and properly masked and goggled. That must happen sometimes. Of course being at least 6 feet away from the closest person is a good thing. It is just the assumption that that is enough to keep people safe from COVID that should be questioned more.

Anyway my quibble with your post was the part about the guidelines being the same. They aren't really. The difference may be slight, but it could be critical.

If you're claiming there's "isn't much evidence" indicating aerosol transmission, I would once again encourage you to read the article closely. There are several well-documented case clusters cited in the article where infections could really ONLY be explained by some degree of aerosol transmission. But aerosols vs. droplets aren't a black-and-white situation: people expel a whole range of different particle sizes, and where we draw the line between droplets and aerosols is largely arbitrary (small droplets just above that line behave much the same as big aerosols just below it).

Small "droplets" can travel some distance too. 6 feet isn't a magical boundary beyond which droplets completely vanish. Nor do particles just below the aerosol vs droplet threshold magically become non-infectious. There's a continuum of behavior. Public health authorities KNOW all this, and have known it from the beginning. But they also know that the public needs simple, clear guidance to take action. So, they have to simplify their explanations and inevitably some detail will be lost.

What we know now is that smaller particles (short-distance aerosols) play a bigger role than initial data suggested. But the evidence still suggests SARS-CoV-2 usually requires pretty close contact or circumstances that concentrate aerosols: limited ventilation on cruise ships, for example, or people singing for an extended period (producing a much higher volume of aerosols).

> I don't deny that if someone with COVID coughs directly in your face which apparently was considered the dominant transmission vector at first

This is not even REMOTELY what "droplet transmission" means. If that was what it took, NOBODY would be getting sick. Droplet transmission can come from talking, or being near someone yelling a drink order in a bar, sharing a cab, attending a dinner party, etc. It just implies fairly close contact.

> Anyway my quibble with your post was the part about the guidelines being the same. They aren't really. The difference may be slight, but it could be critical.

Every single piece of public health advice is imperfect, because they have to simplify complex situations. None of the original safety measures were actually WRONG -- all help protect against short-distance aerosols. The new evidence just adds another layer to the situation, and places extra emphasis on certain measures.

If the public and politicians had actually followed the original public health guidance, the situation would look much better than it does today.

Indeed. Governments have been slow to draw these lessons unfortunately. My local government (quebec) lets you remove masks at indoors events when seated.

Governments are generally slow to change guidance when evidence is limited or ambiguous. The problem here is that while we have pretty solid evidence for short-distance aerosol transmission in some cases, it will take time to understand how BIG a factor it is.

One thing that is easy to forget as a layperson: when it comes to public health, the government only has a limited ability to influence public behavior. Think of it as having a limited number of cards to play. So if they spend a card convincing people to wear masks indoors at events, then they can't spend it convincing people not to hold dinner parties (a common source of super-spreading events).

Furthermore if the government emphasizes something that turns out to be ineffective, then they have even less ability to convince the public change their behavior in the future. This backlash gets worse if they appear to "change their mind" on something. Witness the backlash from health authorities shifting guidance on the importance of mask use in response to evidence of high pre-symptomatic/asymptomatic transmission of SARS-CoV-2.

A huge part of the challenge for public health workers is figuring out what measures to emphasize and how to communicate it.

I'm not saying the government responses are ideal: they almost never will be, especially with a new disease. But I can at least understand why they're slow to change their guidance.

This is true. However, they jumped on the deep cleaning guidance pretty quickly despite limited evidence.

The article makes an excellent argument for the plausibility of indoor airflows being a major transmission vector. But I didn't see anything about ongoing research to quantify the transmission risks posed by aerosols vs. other transmission mechanisms. (Maybe I missed it?)

It's hard to make policy recommendations regarding aerosols if (a) we're not really sure how big a risk factor they pose and (b) the mitigations would be very expensive.

If anyone is in an indoor environment and wants to gauge risk, a portable co2 meter can be had for about $100-$150. Cod2 is a good proxy for indoor pollutants/air exchange, and I’m assuming it is a good proxy for aerosols too.

I use one of these, you can use a portable battery to power it.

https://www.amazon.com/AutoPilot-APCEMDL-Desktop-Data-Storag...

It seems to be an even better proxy for aerosol risk compared to general circulation because co2 is coming from lungs - I might make myself a wearable logger

We're constantly filling the rooms we occupy with aerosols from our mouths. How will this help?

Because we’re also constantly filling rooms with the CO2 that we exhale.

The CO2 meter acts as a proxy for how much exhaled “stuff” is lingering about.

So if your CO2 meter shows that the room is at ~400ppm [:’(], rather than 800 or 1000, then you can deduce that the room is well ventilated.

I’m other words, whatever ventilation removed the excess CO2 most likely also removed the aerosols at the same time.

Considering atmospheric CO2 levels are around 400ppm you're not going to keep it that low indoors unless it's full of open windows.

Yup. I have all of my windows open right now, it’s summer. Co2 tends to be around 500. Even outdoor city air in my location is more like 450, though of course my meter could be biased high.

That’s what I was getting at. 400 is the lower bound, if you have many windows open on a breezy day in the country.

The tear emoticon was a nod to how high that baseline is.

Is there a reliable portable Co2/Pm2.5 logger?

I've heard the accuracy on the Pm2.5 ones at least is way off.

I just moved to a place where I need to keep an eye on Pm2.5 in particular.

It doesn’t log pm2.5. Only co2. For pm 2.5 I recommend a laseregg

Can’t edit: co2 is a good proxy for VOC’s. CO2 is not a good proxy for pm 2.5, to be clear: this depends on the pm 2.5 in your outdoor air.

In other words co2 is a proxy for indoor/outdoor air exchange, and thus should be a proxy for how fast aerosols are sent outdoors.

One key result of this evidence is that we should take all the money going into deep cleaning, and spend it on higher quality masks for everyone. Also perhaps makeshift ventilation systems (being careful not to replicate that Hong Kong restaurant) or outdoor tents where feasible.

What was the restaurant doing wrong? Was it recirculating indoor air? Or was it actually exchanging the air? Replacing indoor air with fresh air from outside.

The article links to the study. The issue was more than certain people sat downwind of others indoors, rather than where the air came from. Let me know if you read a different conclusion from it.

Now I’m really curious. How does one exchange indoor air safely?

As I understand it, the restaurant had an air conditioner in front of a table, and an infected but asymptomatic person was breathing into the airstream which was then circulated to infect anyone downwind of the a/c.

I was under the impression that the aerosol route was just common knowledge, but last week my state government (in Brazil) was doing deep cleaning in schools that have been closed for like 100 days. Yeah, good thing you're deep cleaning probably the last place on earth with no coronavirus! Now we'll only have problems if people want to breath in there... Such a stupid security theater.

Staff may go to schools even when they're closed for students. That may not have been the case there, but cleaning a "closed" school isn't necessarily ridiculous.

Somewhat ironically, people doing that cleaning might spread coronavirus into those places if they happen to be asymptomatic carriers

Yeah, this is the fundamental failure of this administration. Months ago we could have designed a high quality and visually unique mask with less than N95 efficiency but with a reasonable safety and comfort level. We should already have been manufacturing and distributing them at cost. They should be mandatory in all enclosed spaces and we could have prevented a lot of the spike in spread we are seeing now and are likely to see as more and more things open up.

There is no reason to design a worse mask than N95. They could have just manufactured more N95 masks and rationed them to prevent hoarding and speculating. Every household could get an N95 mask ration card to buy masks and decon tools like UV-C lights and sparky ozone generators.

People were not going to fit N95 masks properly or wear them for any extended period.

ADDED: In fact, I'd argue that making N95 masks mandatory (as opposed to face coverings more broadly) would be extremely bad policy even if they were readily available.

You would have to be literally retarded to not figure out how to wear an N95 mask. They fit most people, at least clean shaven ones. You just have to bend the metal nose band to fit your nose and maybe go around the edges of the mask with your fingers. Yes some tiny percentage of people probably have oddly shaped faces and they won't be able to wear them, but that doesn't mean the other 99.9% of the population cannot.

It's very difficult to wear an N95; it's really constrictive and uncomformtable. You can't expect civilians to wear N95 masks all the time and you need to weigh the comfort of a mask against its effectiveness.

People say this, but I don't understand it. I regularly wear N95s for hours on end. It's not fun to do while sweating, sure. But it's not much more difficult than wearing a surgical mask, is it?

Sure the straps are tight and the nose pinches. But that's little discomfort compared to getting sick.

A lot of people already complain about wearing the regular masks and how uncomfortable it is, especially in summer. I'm sure a lot of people don't wear masks already or take it off regularly because it's so uncomfortable. I think ubiquitous use of N95s would just make that problem worse.

>> But that's little discomfort compared to getting sick

Depends on how afraid you are of getting sick. Most people that get infected do not develop any symptoms, and of those who do 95% wouldn't be able to tell them aparat from the normal flu. The only real risk group are people over 70, and while those might actually be afraid, the rest of the society is simply getting more and more pissed off with all those restrictions imposed on us.

Yeah, I'm not trying to say that everyone shouldn't wear an N95, but from a pragmatic standpoint they won't. People will barely wear one today that is made out of a t-shirt and barely fits. I just think we'd get better results meeting people halfway.

Have other countries done this? Is the US the only country that has seen a spike as things open up? Just interested in the comment “failure of this administration,” when I haven’t seen such attempts in other countries either. Perhaps this is a failure of the WHO? There hasn’t been any notable proposals from Congress in this issue either. Were people advocating such a solution and it was ignored? Because hindsight is 20/20. As late as Feb 28, there were politicians advocating people visit restaurants in Chinatown SF and calling travel bans racist. Was that a failure too?

The point of my comment is that we can talk about “failure,” but it’s disingenuous to suggest that the right answer existed all along but it was ignored. Nobody had the answers other than perhaps Taiwan when they sealed borders on 31 December — and Taiwan was ignored because of WHO politics.

Regardless of if a new standard for masks would help (it would), the federal government's official position on masks is an obvious failure if you're paying attention, given that the first time President Trump wore a mask was July 11, 6 months after the virus should have been known to top officials in this administration.

(In particular, a surgical mask is better than nylon netting and "N95" doesn't describe how exhaled particles are treated. An N95 mask with an unfiltered exhalation valve has the wearer exhaling droplets all over the place.)

It is common knowledge. They are doing the deep cleaning as a means to calm the masses. They know it does not really go any distance towards solving the issue but they don't want / have the funding nor the political capital to address the ventilation issue.

There is a weird disconnect. Everyone seems to acknowledge the most likely way to transmit COVID is via droplets when indoor. Yet, there is little discussion about ventilation. Maybe people felt like there was less they could do?

If I had to guess, it's because sanitizing surfaces all day is cheaper/easier than upgrading the ventilation system.

I think this is it. Everyone's painting the roses red because spritzing some sanitizer on every surface costs a minuscule fraction of the massive revamping of indoor climate that's actually required to reduce risk.

>Maybe people felt like there was less they could do?

Probably mostly that plus a lot of the attention focused on transmission by touch early on. The last event I went to in March there was no handshaking, cleaning of surfaces, etc. But no masks or distancing.

But, yeah, taking additional care to clean surfaces is pretty easy and cheap. Completely redoing ventilation is going to be pretty much impossible in a lot of situations.

Gyms and restaurants have had their air conditioning off in Aus. Israel turned off their bus air conditioning.

This isn't breaking news but I suspect it would be a new angle to the media rhetoric for a few countries and media outlets.

Fluid dynamics are notoriously complicated. And AFAIK we also lack good models for how long any particular aerosol cloud remains dangerous over time / travel-distance. That makes it really hard for (most?) anyone to quantify the risk level of a particular environment, or to design a mitigation with well-understood risk/cost tradeoffs.

Compare that to a simple ballistic model, where:

- most adults can intuitively grasp and apply such a model, and

- it's somewhat easier to calculate a risk/cost tradeoff for mitigations.

That's why I wish there would be more UV sterilization going on. Maybe in addition to more air flow, have a person or mini bot go down shopping aisles and sterilize the air.

We probably aren't hearing about it because it's something we have less ability to protect against.

I remember a popular comment here a while back mentioning that epidemeologists' job is partly public relations, trying to figure out what they can tell the general public that will minimize the viral spread.

Making sure everyone wears masks will, at the scale of the general population, reduce the infection rate by some noticable percent. It's also something everyone can do, and it gives everyone a sense of control over the situation - enough of a sense, at least, to prevent chaos.

Talking about airborne transmission, though? The kind of masks that can protect against that are hard to come by. Not to mention that the virus could enter via the fluid of the eyes (not trying to add conspiracy here, just trying to make a point about the difficult reality of preventing infection [0]). Bio-rated goggles and N95+ rated masks are more than we can expect from a public that's making face masks out of bandannas.

I think we're seeing very pragmatic statements being made, that are tailored to a public that can't enter full biohazard mode and need to not panic.

[0] https://www.biorxiv.org/content/10.1101/2020.05.09.085613v2

> Talking about airborne transmission, though? The kind of masks that can protect against that are hard to come by. Not to mention that the virus could enter via the fluid of the eyes (not trying to add conspiracy here, just trying to make a point about the difficult reality of preventing infection [0]). Bio-rated goggles and N95+ rated masks are more than we can expect from a public that's making face masks out of bandannas.

plenty of evidence that even a little bit of protective gear helps. it isn't a matter of hazmat-suit-or-GTFO.

> Making sure everyone wears masks will, at the scale of the general population, reduce the infection rate by some noticable percent.

I said that.

I think that's what the parent was saying. The widespread wearing of just about any face covering seems to help on net even if it's probably >50% about protecting other people. Even if higher-level protective gear were readily available, most people wouldn't wear for any length of time and it wouldn't be fitted properly. So just wear something seems to be the most reasonable advice for the general population.

Do you have proof that people would not wear better protection and that it would be ineffective even if they did to due fit issues? Or are you just making an assumption?

The fact that N95 masks were and still are selling for such high prices seems to be evidence against this view. I assume this view is most popular among Americans because Americans seem to represent the majority of anti-maskers.

Where I live everyone wears a mask but very few people wear N95 masks simply because they are more expensive and hard to find. If COVID is short range aerosol infectious as some evidence suggests greater N95 mask availability and usage may affect infection rates at least outside of the US. How significant a difference this might make is simply unknown at this time.

I am a little confused. It seems that most people knew it was a risk; that's why stores, gyms, churches, etc were closed in the first place, wasn't it? Together with the warnings to avoid inner spaces.

UV-C light in your air conditioning unit or some higher end filters might solve the recirculation issues, no? When people must be inside, we could probably make it much safer for them to do so even without the equipment you mention.

> might solve the recirculation issues, no?

No.

Another half-baked 'solution' will cut the infection rate by some fraction of a percent, and we'll be right back where we were before: right here, asking why we aren't being told about proper solutions.

Just like the masks, which as TFA is discussing, don't actually address one of the primary transmission vectors.

One problem is that no one seems to know that AC systems recirculate air. I literally can't get people to believe me when I tell them this. When buying a window unit recently, some models had the ability to incorporate fresh outside air but the cheaper ones didn't. My home is leaky enough that I worry more about keeping outside air out rather than in, though.

The ones that bring in outside air (that I have seen) just let a little outside air in. Most of the air is still recirculated, but there is a tiny hole that opens to let some air in.

Do people not use the recirc switch in their car?

I think this actually makes it more understandable. If recirc is a special mode you have to activate in your car's AC, then it's reasonable to assume it's not the default mode for your house AC too. Since they never had a 'recirc' button to press at home, they'd assume it doesn't recirculate. Reasonable, but inaccurate.

Unless someone who has it is inside your home I don't think you need to worry about the air recirculating. I agree though its amazing that people don't understand how this works.

There's one key paragraph buried in the article that will help a lot of people:

> However, to date, there is also no evidence of truly long-range transmission of COVID-19, or any pattern of spread like that of measles. Screaming “it’s airborne!” can give the wrong impression to an already weary and panicked public, and that’s one reason that some public-health specialists have been understandably wary of the term, sometimes even if they agreed aerosol transmission was possible. Cowling told me that it’s better to call these “short-range aerosols,” as that communicates the nature of the threat more accurately: Most of these particles are concentrated around the infected person, but, under the right circumstances, they can accumulate and get around.

Translation: people can get infected further away than with larger droplets -- especially in stuffy, enclosed environments -- but distance still reduces the risks.

> people can get infected further away than with larger droplets

Minor nitpick, you can think of aerosol transmission as plume of virus particles. Technically you can get infected long after the carrier has left a closed room, at which point the concept of being "further away" stops applying.

That's true, in this case "further away" is a 4-dimensional distance vector (it includes time). :D

A couple other articles I've read in the last few days also cover this topic:

Yes, the Coronavirus Is in the Air

> Transmission through aerosols matters — and probably a lot more than we’ve been able to prove yet.

...

> I am a civil and environmental engineer who studies how viruses and bacteria spread through the air — as well as one of the 239 scientists who signed an open letter in late June pressing the W.H.O. to consider the risk of airborne transmission more seriously.

https://www.nytimes.com/2020/07/30/opinion/coronavirus-aeros...

Aboard the Diamond Princess, a Case Study in Aerosol Transmission

> A computer model of the cruise-ship outbreak found that the virus spread most readily in microscopic droplets light enough to linger in the air.

https://www.nytimes.com/2020/07/30/health/diamond-princess-c...

And here's an article from two weeks ago that goes into some depth on superspreading events:

https://www.washingtonpost.com/health/2020/07/18/coronavirus...

> He believes ventilation may also be to blame for a case involving a young man from China’s Hunan province, who sat in the back of a bus but ended up infecting seven others in various areas of the vehicle and then two more on a second minibus he hopped onto next. Li interviewed the patient, driver, passengers and reviewed video footage and found it odd that few of those who became infected were nearby. In fact, at least one passenger who fell ill was as far away as possible at the front of the bus — 31 feet away — from the coronavirus-positive man. […] In the case of the Hunan man who transmitted the virus while riding two buses, Li said that “amazingly” after that four-hour window of infectivity, he is not known to have infected anyone else at all.

I would like to make a small point about the letter signed by "hundreds of scientists around the world".

According to the NY Times there were in fact 239 signatories, which coincidentally is almost the same number as the "253 ... scientists from 44 nations" warning of the dangers of electromagnetic radiation (!) that can be found at https://emfscientist.org/ . If you trust one, do you trust the other also?

Regardless of the merits of the rest of the article, I would caution against trusting a claim just because two hundred odd scientists from all sorts of disciplines were willing to sign an open letter. Science is not a democracy.

The “appeal to authority” is also used to sell toothbrushes. I agree that it’s foolish to trust an article or “fact” because 9 out of 10 doctors agree. I am very interested in why that 10th doctor didn’t agree..

The amount of unknown and disagreement after all this time and money spent is a big failure of science. Laymen have a unique peak into how science works day to day, which might be good or bad depending on how you see it.

Yes it's a well written article by a clearly intelligent author who did his homework and knows his sources and of course we should never have ruled out short range aerosols. It's ridiculous. I think it only happened because so many people just believe whatever authorities like the CDC and WHO tell them without any critical reasoning applied. If these health agencies had not effectively ruled out the possibility afaik without any supporting evidence maybe there would have been more research to figure out droplet sizes and travel paths under various airflow conditions. Currently everyone seems to just want to make assumptions and stick to them, but that isn't science even if you call yourself a scientist.

Maybe also N95 masks would have been considered essential not only just to health care workers and maybe more effort might have been made to supply some to the general population. Currently 3M for instance voluntarily stopped selling their masks except to hospitals and speaking of those masks there is also not enough research on effective ways of decontaminating those masks without reducing their filtration effectiveness so that they can be reused more often and so that more can be made available to the public instead of effectively making them hospital only.

i wish target and home depot would stop making us wait in line while they futz about wiping things down. it's been clear that time spent in line with other people is a bigger concern than the possibility that something is lingering on the barcode scanner and will be transferred onto my box of nails, or bananas.

At the beginning of the epidemic, joe rogan hosted M.Osterholm for an interview where he warned about a lot of the things to come: the rapid spread, the small effect of washing hands or masks, the airborne spread etc. It's sad that the epidemic seems to have turned worse than most ppl assume it would.

https://www3.nhk.or.jp/nhkworld/en/news/ataglance/855/

From April, Japan has been on top of this for a little while. Impressive science imho.

And yet Japanese government declared victory and campaigned against protective measures leading to a massive re-ourbreak, "for the economy"

Japan has some really impressive universities and, as a rich country, is able to nurture all sorts of talent.

The Japanese ruling party is a bunch of old people from a few traditional families mixed with some new faces.

It’s very unfortunate how little these two worlds (talented people and politicians) collide.

This comes to mind every time I see a company/business emphasize how much priority they're putting on keeping people safe, and then only speaking about disinfecting every surface throughout the day.

While it doesn't hurt to keep surfaces clean, we continue to see evidence that the majority of cases have come from airborne spread in an enclosed environment with poor ventilation.

If there's any lasting change to building environments that comes out of this, I think it should be an overhaul of building ventilation codes to require/heavily incentivize systems that replace air rather than circulate it.

Because wiping high-contact surfaces a few times a day is cheap, easy to do, and highly visible. And, hopefully, an easy extension of nightly cleaning that was already happening.

Reworking your HVAC system to provide better circulation, filtration, and/or more fresh air is expensive, often an ongoing cost, and probably invisible to the end customer.

I guess you could say it's well-intentioned virtue signaling.

in the UK the LNER train company highlights ventilation amongst other things, but the ventilation bit I found suprising when I encountered it.

https://www.lner.co.uk/travel-information/lets-travel-togeth...

" Our onboard ventilation systems are providing a continuing supply of fresh air which is cycled every 6 minutes limiting droplet transmission between passengers." With the graphics implying that ventilation is spatially limited.

The closest to air-conditioning possible in trains like LNER's is more similar to individual window units (except mounted in the ceiling) than the integrated systems in larger homes or offices.

LNER operates two types of multiple-unit from the same family (a conventional EMU and then a bi-modal hack of that concept because the Tories don't want to spend money electrifying more of the railway), and then an older loco-hauled passenger service where a type 91 is pulling and there's a train of mostly passive passenger stock behind it.

In both these designs there is electricity available, to run the air conditioning units, but it's not practical to pump air around the train so they don't. The air in your part of the train will get recirculated by the fans that make the air conditioning unit work, so I'd expect that if you spent an hour on a train four seats from an infectious person there's a decent chance you'll be infected. But air from other carriages isn't recirculated into yours at more than negligible level.

Because these are mostly doing intercity journeys (thus fewer stops, and perhaps dwelling for longer at each) even the newer EMUs were not designed as a single huge tube like the modern Tube stuck or some local EMUs. So there's a "double airlock" partition between one carriage and the next which reduces noise and discomfort but makes getting on and off take a little longer. In this particular case it probably makes the train slightly safer to use.

I am sympathetic to what the WHO did here, they realize that the average person is going to be extremely fearful when they realize that stagnant air could contain virion particles hours after being sneezed in (which is what the data show).

They should have erred on telling people, because then we would have had months to ramp up room air purifiers before school starts... (I have been saying this for months, and am surprised by the lack of scientific leadership in ‘science’ organizations).

Why should the WHO not incite fear if the fear is entirely rational and justified? People not being afraid enough is exactly how people die.

Just look at the list of people who signed the letter.

They are experts in their field but they don't have the expertise to consider the whole picture.

It's possible, that there is some airborne transmission besides droplets, but there is no evidence that it's significant transmission route. To get infected you need big enough dose of virus at once. Just some dry floating particles in the air is not enough.

There is this startup which came up with the solution for the airborne problem.

https://yourstory.com/2020/07/startup-bharat-kanpur-crestkit...

There are no receptors in the mouth, only nose and eyes. So the mouth does not need to be protected passively, the only problem is that the mouth is the only actor to spread the virus effectively.

I think we can't talk about it because there is no agreement on terms, modes of transmission, etc. and public policy cannot be based on ambiguous terms (though it can be based on imperfect data).

Talking about airborne transmission would make it too obvious that masks are pointless security theatre. Can't have that

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