Covid-19 Superspreader Events in 28 Countries: Critical Patterns and Lessons
quillette.com
quillette.com
This is something straight out of a TV crime show:
> As the authors note, the restaurant in question was air-conditioned on the date in question. Using video footage, they were able to chart the position of every diner in the restaurant, and then map their subsequent infection status in relation to both the single infected individual known to be present at the time and the air conditioning system’s outgoing and intake streams. If the primary transmission mode of COVID-19 were by small, sub-Flüggian airborne particles, the presence of the forced air convection might have made the environment safer (especially since “smear samples from the air conditioner [itself] were all [COVID-19] nucleotide negative”). But the researchers instead found evidence for the opposite: “The key factor for infection was the direction of the airflow,” with downstream individuals being most at risk—a result consistent with the thesis that COVID-19 is transmitted primarily through the ballistic transmission of large respiratory droplets.
I could easily imagine that having been a key insight in an episode of "Bones" or "Elementary".
(If you are looking for something good to binge watch during COVID "stay at home", I recommend "Elementary", currently on Hulu and CBS All Access. It's a Sherlock Holmes set in modern times series. They did a really good job of taking many characters and plots from the original stories and adapting them in such a way that if you read the stories you will recognize them and perhaps even think you know what is going to happen--but they have changed just enough that the ending will still surprise you but also be eminently reasonable in hindsight. The stories that aren't obviously based on any particular original are equally good).
> But the researchers instead found evidence for the opposite: “The key factor for infection was the direction of the airflow,” with downstream individuals being most at risk—a result consistent with the thesis that COVID-19 is transmitted primarily through the ballistic transmission of large respiratory droplets.
If the direction of airflow is the key factor, then the droplets have to be moving with the airflow, and therefore not ballistic.
Am I missing something?
Then again, it's not aerosolized as it didn't diffuse homogenously into the space. It's somewhere in between.
When these guys are saying "ballistic", they mean that the droplet is big enough that gravity is important, and that it's going to hit the ground in a reasonable amount of time and not hang around in the air until convection/diffusion spread it evenly throughout the room.
Imagine how bad Austin would have been if SXSW had actually gone ahead given how hellbent they were on going through with it. It would have been much much worse state than it is now. It is a positive that the government listened to health officials and shut it all down despite the complaining to the contrary. Economies never work well in sickened environments.
But what I found interesting about the article (and it is long read) is his hypotheses on mode of transmission. Which is the "direct ballistic delivery of a large-droplet Flüggian payload from face A to face B" and that means that interventions like the "expanded use of masks and social distancing is critical" And we should also speak softly, avoid “coughing, blowing and sneezing,” or exhibiting any kind of agitated respiratory state in public, and angle their mouths downward when speaking."
But he does warn that he is a Computer Scientist rather than having any medical background.
Even diseases with low transmissibility are known to be disseminated by public transit, such as tuberculosis.
> I am not an epidemiologist, let alone a virologist. And the data I am working with is substandard anyway, as there are all sorts of obvious selection biases at play, including the editorial biases of the journalists on whom I rely for local reports.
I think a better thing to do would be to refactor the disclaimer and put it at the top/start of the article.
Japan
> Less than two weeks later, she tested positive for the virus, and the authorities swiftly alerted others who had been at the club. As more infections soon emerged from three other music venues in the city, officials tested concertgoers and their close contacts, and urged others to stay home. All told, 106 cases were linked to the clubs, and nine people are still hospitalized.
Singapore
> Singapore's biggest cluster of Covid-19 patients, traced to a restaurant in Jurong, had more than just a dinner in common, said Ministry of Health director of medical services Kenneth Mak yesterday.
> "We've recognised that many of the individuals linked to this particular group of people getting infected had many common social activities," said Associate Professor Mak, pointing to other gatherings such as singing classes that infected individuals had taken part in together.
> "So, in fact, their social interactions went well beyond the dinner in that particular location, and as a result of those close activities... that's where the spread is actually occurring," he said.
Washington was at a choir, where everyone would have known each other
> Health officials said all 28 choir members who were tested for COVID-19 were found to be infected. The other 17 with symptoms never got tested, either because tests were not available or — like Comstock and Owen — the singers were under the impression that only people in dire condition were eligible.
I'm not even sure how you could come up with numbers on how much viral exposure is needed to infect someone, short of controlled experiments with volunteers. The odds of killing a few volunteers seems pretty damn high, especially if you are testing with more vulnerable folks to establish a differential estimate. That's not a study I'd want to be involved in on either side of the clipboard.
The only sizable population of people that I still see out in public that aren't wearing masks are joggers. I wonder if and when we will put a stop to that.
Really??
The UKs advice is to wash hands but not to use a face mask. Hand washing is essentially free but the cost of producing reusable cotton face masks for every single person would likely be ~ £1 billion. If that is money wasted, it is still extremely small compared to the economic devastation which could cost the UK government ~ £100 billion [1] and the economy as a whole significantly more
If there had been massive stockpiles available, the message would have likely been different.
Meta-studies show that the effectiveness of hand washing alone is minimal https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4891197/
https://www.who.int/news-room/commentaries/detail/modes-of-t...
> In an analysis of 75,465 COVID-19 cases in China, airborne transmission was not reported.
(This is also a reason masks can be effective despite the virus particles being smaller than what masks can stop; you don't have to stop the particles, but the much larger drops they're contained within.)
It's more complicated because there are actually 4 mechanisms that might stop a particle from getting through.
1. For particles bigger than the gaps, it does work like a net as most people expect.
2. For particular smaller than that but massive enough that they cannot change direction fast enough to follow the air stream they can miss turns of the air flow and get embedded in the fibers.
3. For even smaller particles they can get jostled around significantly by hits from gas molecules (like with Brownian motion). This can knock them into fibers where they can become embedded.
4. Some filters materials have an electrostatic effect that can attract and hold passing particles.
One of the reasons filters are commonly rated by their efficiency at 0.3 micron is that this is in the region where the filter is least efficient. For bigger particles, the gains from #2 and later #1 more than make up for #3 being irrelevant at those sizes. For smaller particular, the gains from #3 increase efficiency.
So you have the filter roughly getting worse down to the 0.3 micron ballpark, and then getting better as particles become still smaller, and at some point as you continue getting smaller it is going to get worse again. (I don't know where that final turn around is).
I understand the distinction, but the terminology should be renamed imho, to something like "epidemiologist airborne". Because to the layperson it definitely is transmitted "through the air", implying again in everyday terms "airborne transmission".
e.g. read this : https://wwwnc.cdc.gov/eid/article/26/7/20-0764_article
and look at the associated diagram:
https://wwwnc.cdc.gov/eid/article/26/7/20-0764-f1
Those people were NOT all within six feet of each other.
The German auto part plant paper also details transmission where nobody sneezed or coughed at a short business meeting.
As that study discusses, they were in the path of an air conditioner. The "six feet" thing is a rough estimate, not the Eleventh Commandment.
By contrast, measles has an rFactor of 17, because it is an aerosol. It is 6x more contagious. And as an aeorsol, simply breathing next to a person who is infected is enough for you to contract the virus.
Airborne is not the same as aerosol.
Put another way. If there is a person infected in a house hold with coronavirus, not everyone is guaranteed to get it, because it is only airborne.
If someone has the measles in a house hold, and there is no vaccine, then everyone will get it, because it is an aerosol.
> In an analysis of 75,465 COVID-19 cases in China, airborne transmission was not reported.
"They will not stay suspended in the air" means it's not airborne. An airborne disease is one that does stay suspended in the air.
It's recently been revised up to 5-6 [0], and mortality estimates reduced.
https://www.forbes.com/sites/tarahaelle/2020/04/07/the-covid...
The CDC paper [1] estimated that the R0 value may have been 5-6 in Wuhan, during lunar new year, and before the public was ware of the virus.
Alternatively, the R0 value is now <1 in the US and the spread is decreasing,
Evidence out of NY today says it’s possible 14% of the state has already been infected. That’d point to a pretty high value.
https://www.wxxinews.org/post/random-test-finds-nearly-14-ny...
IF new cases today are less than yesterday, the R0 must be <1 one incubation period ago. That doesn't mean that R0 wasn't different a month ago, or will be the same a month from now.
That's a big if. We don't have enough testing in place to determine that currently. The reported number of cases and the actual number of cases are not the same right now.
Positive cases have stayed roughly the same since April 4th while testing increased. For R0 to be greater than 1, we would have to be worse at testing.
https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/test...
(Direct link: https://www.cdc.gov/coronavirus/2019-ncov/images/lab-specime...)
We've been basically flat since mid-March.
I think the point still stands unless you think we are identifying a lower proportion of infections
I do. https://www1.nyc.gov/assets/doh/downloads/pdf/imm/covid-19-d... indicates many areas of NYC are seeing more than 57% positive results; that likely indicates we're not even scratching the surface. We're simply not that good at identifying who to test.
The estimated r0 of 2/3 is hilarious. less contagious than sars eh? No amount of down-voting me or cdc papers is going to convince me of that.
https://web.mit.edu/jeffrey/harris/HarrisJE_WP2_COVID19_NYC_...
How hard can it be to find 100 similar workplaces, and to 33 of each say "You guys must wear masks". "You guys must have all windows open all the time". "You guys must wear gloves all the time".
Then wait 5 days, and see how infections spread.
That activity might lead to the deaths, in the worst case, of a couple of workers. Yet the knowledge gained would save tens of thousands.
You can skirt around the ethical issues by giving Sample A an unlimited supply of free masks, and keeping Sample B as the control sample. Even with free masks, not everyone in A will wear a mask. And some in B might still bring their own masks. But A will have higher mask use on average, and with large randomly selected populations you can tease out the impact using IV regression[1].
[1] https://en.wikipedia.org/wiki/Instrumental_variables_estimat...
* Social habits of the company
* Number of infected people within the company
* Compliance with the protocol
* Age demographics
* Infection rates from places other than the company
* Weird selection bias resulting from the company needing to not lock down to begin with
Very, very difficult study
* We don't have the resources to test sufficiently large numbers of companies like this
* The dependent variable in question is going to be entirely dependent on the number of people infected at a company at the beginning of the study, which is unknowable unless you can test everyone... which we can't.
Or, to put it more bluntly, a modern ethics committee would have rejected the idea of installing sewers in cities to prevent disease because one builder of the sewer might have died in the process. Without that, industrialisation probably would never have happened, and we'd all be subsistence farmers today.
Because it was thought unethical to conduct studies around masks and infectious disease, the evidence was sparse, so the WHO and CDC didn't recommend wearing them. This has directly led to tens of thousands of deaths.
"The institutions through which Americans build have become biased against action rather than toward it. They’ve become, in political scientist Francis Fukuyama’s term, “vetocracies,” in which too many actors have veto rights over what gets built. That’s true in the federal government. It’s true in state and local governments. It’s even true in the private sector."
You get to choose whether to be in the business of installing sewers. Saying that it's ok to force people into medical experiments against their will for the greater good is how you get Nazi holocaust atrocities. Medical ethics has a long history that it sounds like you might enjoy spending some time reading about.
I'm disappointed by your false equivalence between being told to stay home and safe and being made into a guinea pig.
If being home and safe means you lose necessary income, then your ire should be directed at your governments at all levels for refusing to prepare critical safety nets and regulatory environments that would make it possible for you to stay alive and safe without laboring every day. But advocating a regression on everything that history has taught us about medical ethics is terrible and bad. We're talking about thousands of years of accumulated and refined history lessons here. Medical ethics is a perfect example of why learning history is important.
This is the false equivalence. How long does one have to stay home in order to be "safe"? If things calm down now, will they be worse in the winter? Will we still have to be "safe"? How do the consequences of curve flattening strategies that look more like half-hearted eradication attempts be compared to approaches that look literally like curve flattening?
Noone knows these answers.
This has economic repercussions. A good amount of meat processing plants are now idled because the workforce is off sick due to lack of protective equipment and sick leave. We are looking at meat shortages. I hope people make the right connections.
If people start to starve because we stopped being able to produce food or people start dying of other causes because our basic infrastructure start collapsing, then you can start talking about ethical dilemmas.
I think its a safe bet that this is already happening on small scales. Noone is measuring the degree.
There may be images of long lines of unemployed people that have to get from the government or food banks, but the food is still there. Farmers are still producing, distribution networks are still working, essential services operating. That part of the economy is still going.
And then look at the infection spread in each country.
the primary mechanism of transmission (droplets into the nasopharangeal area) has been known since at least february (when it started to become regular news here in the US) and probably since at least december in china when it became a known infectious agent.
the better we understand the situations and environments where transmission is materially increased, the faster we devise reasonable mitigations and get back to some semblance of normalcy.
it's also important to debunk false mitigations that only serve to mollify the skittish (e.g., elaborate germophobic rituals) and thereby obstruct understanding and cause other harms. in fact, some of those mitigations can increase transmission risk simply by providing a false sense of relief (e.g., constant, but inevitably incorrect, mask usage).
I thought the entire point of this post was that there were multiple competing theories and little agreement or certainty? Your use of the phrase "has been known" implies a broad consensus in public health circles. I've seen very little consensus on any feature of this pandemic.
> "When do COVID-19 SSEs happen? Based on the list I’ve assembled, the short answer is: Wherever and whenever people are up in each other’s faces, laughing, shouting, cheering, sobbing, singing, greeting, and praying. You don’t have to be a 19th-century German bacteriologist or MIT expert in mucosalivary ballistics to understand what this tells us about the most likely mode of transmission."
For extra credit, spray in their mouth through a basic cloth mask.
So the question is does the 2m separation push the averages towards that? I would think it does. Partly because the number of people within a blast radius of a cough or sneeze is much lower, and secondly the probability of infection drops with distance.
Social pressure that then drives coughing and sneezing people home in a social distancing environment probably reinforces the effect of reducing transmission rates.
Is it enough? That will have to be measured and analysed probably much later.
Interesting. Having spent some time in SF, can attest that the homeless - on occasion - appear to have super human immune systems.
This is a super interesting point of view.
That's the whole reason behind social distancing right? To reduce the likelihood that you will contract the virus from someone else. It's not so much about keeping from getting other people sick, it's about keeping yourself from getting sick.
As someone with young kids and a more frequent exposure to norovirus and other stomach bugs than I'd like to admit, once that gets into the family, everyone gets it. The way to avoid it is to not go places where your kid is going to pick it up (public library usually), but in general you still go to those places because they are convenient for other reasons.
I understand the focus on handwashing and sanitizing things, but that doesn't do anything for direct exposure. If the stomach bug is near you, you're getting it. I assume coronavirus is going to be much the same.
Just throwing it out there, I think this is likely going to be true, and the populations with higher proportions of old people are going to see greater infection rates than populations with fewer old people. That is to say, those who are vulnerable to the disease have a greater likelihood of getting other people sick than people who are naturally resistant to the disease but will behave irresponsibly. If you had a city with nobody over age 50, not only would the death rates be trivial due to the health of the population, but the spread of the virus would be very small.
I also don't think the views here hold once a non trivial proportion of the population is infected, like we have now, so it probably doesn't matter and is hard to act on anyway.
The work done in the restaurant paper is really good. It was a clever natural experiment but clearly was a lot of work to piece together.
In the end the overwhelming majority of people are not throwing down thousands of dollars per day at bars and restaurants.
As the old parable goes, maybe it doesn't make a difference to all those thousands of starfishes washed on the shore, but it made a difference to those few the boy threw back into the sea.
A small percentage is going to be quite concentrated, but at that point you’re not really talking about Austin. Just the people actually running the event.
In terms of impact on local small business it’s still a small revenue bump as SWSX pushes tourists to chose other dates or other cities with cheaper hotel rooms etc. Further, most companies don’t have the slack to really benefit from such events. Something like a 2-3 percent boost in a local bar’s annual profit seems possible, just not that important relative to a shutdown.
Anecdotally I know of many people who work year round to prepare for an event at SXSW and rely on it for their entire annual income.
Cancelling SXSW is a big deal to this city. It hurts. It's not to be downplayed.
[1] https://austin.culturemap.com/news/city-life/09-27-17-econom...
That’s 350M number is also extremely suspect, at a minimum including existing city residents as the hotel reservations are vastly below attendance.
Still even assuming that 350M was correct and not ridiculously inflated it’s 350/146,000 = 0.2%.
The GDP per capita was simply a sanity check showing how 1.4B must be wildly wrong.
https://en.wikipedia.org/wiki/List_of_U.S._metropolitan_area...
Is that $350 million into the city taxes, or just $350 million for some private citizens, apparently some of whom you know and for whom it is undoubtedly a big deal.
https://explore.sxsw.com/hubfs/2019%20SXSW%20Economic%20Impa...
There's a big halo effect on these sorts of things. When hotel rooms get booked, housekeepers get more hours, bartenders get more tips, restaurants get more covers, etc.
For the event itself you also have the carpenters who assemble the stages, security staff, garbage runs, etc.
There is some logical fallacy here. Large droplets don't exclude aerosol transmission, so you can attribute to it everything you attribute to large droplets too. There are also such superspreading events of whole building getting infected past lockdown, like the whole family dorm building getting infected where people share bathrooms and such.