How Coronavirus Spreads (airborne update) | Hacker News Reader

How Coronavirus Spreads (airborne update)

cdc.gov

44 pointskjhughes13 comments

To minimize confusion some scientists are calling for the clearer terminology for describing transmission through the air. A recent letter in Science argued that we should use the terms “aerosols” vs. “droplets” with a size threshold of 100 μm which “more effectively separates their aerodynamic behavior, ability to be inhaled, and efficacy of interventions”. [1]

[1]: https://science.sciencemag.org/content/early/2020/10/02/scie...

Why does the CDC keep flip flopping on this?

I think it's to try and reduce demand for N95s among the general public

Isn't there a better way to do this?

Initially, CDC recommended against face masks for fear of N95 shortages (in retrospect a mistake because non-N95 face masks can reduce the spread of virus without impacting the supply of N95 masks). The more recent shifts in messaging are likely due to our evolving understanding of COVID-19 and (sadly and hopefully temporarily) due to political considerations.

So instead of stating the facts they’re experimenting with different ways to manipulate our behavior?

Yeah I don’t understand how people are okay with this version of reality. The CDC (and WHO?) lied to us “for our own good” and apparently the resulting loss of trust in these major governmental organizations was worth the lie.

My social media was much more accurate than the CDC in the first half of the year.

Because the medical profession defines "airborne transmission" differently from the colloquial use of "airborne transmission" and they keep not making that clear.

"Airborne transmission" from a medical perspective is where very small number of virus particles can ride things like dust and then infect someone. These diseases are extremely contagious and extremely persistent in the environment. And no mask (not even N95) will help for these.

Covid19 basically requires virus in water droplets to transmit. Consequently, it requires close contact and time to transmit. So, yes, it transmits through the air but isn't an "airborne" disease as the water droplets seem to be a required vector.

This is why even simple masks are quite effective against Covid19, because it requires water droplets to spread.

Thus we have anecdata like this:

"Starbucks outbreak infects 27 customers but spares mask-wearing employees" https://covid19data.com/2020/08/25/starbucks-outbreak-infect...

> Covid19 basically requires virus in water droplets to transmit.

“Requires” is too strong a word given our current understanding. The CDC update states that “There is evidence that under certain conditions, people with COVID-19 seem to have infected others who were more than 6 feet away. These transmissions occurred within enclosed spaces that had inadequate ventilation.”

That said, COVID-19 is still thought to spread mainly through close contact, so the parent’s Starbucks example probably holds true as a pattern.

Fluid physics says otherwise

"Thirdly, we show that even simple mouth-and-nose covers made of good filter material cannot reliably protect against droplet infection in contaminated ambient air, since most of the air flows through gaps at the edge of the masks. Only a close-fitting, particle-filtering respirator without an outlet valve offers good self-protection and protection against droplet infection"

https://www.researchgate.net/publication/342693523_Fundament...

There's rather too much "magic of the mask" conclusions being drawn without considering other factors.

Nor is there consideration of the other issue. If you catch a disease while the mask is off, then when you put the mask back on you're breathing your own shedding back into different parts of your respiratory tract.

Similarly, it's been shown that surgical masks don't do that much even in surgical settings: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4480558/

From your own link, just to be clear, "Nevertheless, wearing simple homemade or surgical face masks in public is highly recommended if no particle filtrating respiratory mask is available."

But no scientific reason why that is the case.

Which means that is just the usual line you put in papers to deflect criticism.

Science is about the confirmation and rejection of hypotheses by experimentation and evidence, not truth by repeated assertion

Because "We are still learning about how the virus spreads and the severity of illness it causes"

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