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Why aren’t we talking more about airborne transmission?

theatlantic.com

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Re: Why aren’t we talking more about airborne transmission?

#201

Post by DoingIsLearning »

CogentHedgehog wrote: post #178

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, so…

> 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.

Re: Why aren’t we talking more about airborne transmission?

#202

Post by graeme »

driverdan wrote: post #199
function_seven wrote: post #116

Earlier quoted context omitted.

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.

Re: Why aren’t we talking more about airborne transmission?

#203

Post by csours »

droopyEyelids wrote: post #127
csours wrote: post #107

Earlier quoted context omitted.

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

Why don't you read the article? The distinction is between aerosols and droplets, in the case of corona virus, and by asking this question it looks like you're chasing the wild goose that OP brought into this thread.

Up front: I am not a virologist; I am not saying these things are true, I am saying this is my understanding of this discussion. I am also not saying that Sars-Cov-2 can spread by small dry particles.

I think there a 3 distinct things going on, at least.

Large Wet Particles (droplets): easily caught by masks, fall quickly (3-6 feet), make surfaces infectious, cause infection by touch.

Small Wet Particles (aerosol type 1): Hang in the air for at least 30 minutes. Infectious if breathed in. Mask is less effective (but not ineffective)

Small Dry Particles (aerosol type 2): Hang in the air for 12 hours. Infectious if breathed in. Infectious by touch. Mask is less effective (but not ineffective). Most viruses are not viable as dry particles.

Re: Why aren’t we talking more about airborne transmission?

#204

Post by briandear »

snarf21 wrote: post #37
unclesaamm wrote: post #7

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.

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 li…

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.

Re: Why aren’t we talking more about airborne transmission?

#205

Post by function_seven »

driverdan wrote: post #199
function_seven wrote: post #116

Earlier quoted context omitted.

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.

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.

Re: Why aren’t we talking more about airborne transmission?

#206

Post by throwaway_pdp09 »

prox wrote: post #200
throwaway_pdp09 wrote: post #188

Earlier quoted context omitted.

> 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 a…

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"

Re: Why aren’t we talking more about airborne transmission?

#207

Post by cactus2093 »

jtbayly wrote: post #68
jennyyang wrote: post #32

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 peo…

> 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 take…

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.

Re: Why aren’t we talking more about airborne transmission?

#208

Post by lmilcin »

prutschman wrote: post #157
SkyPuncher wrote: post #118

Earlier quoted context omitted.

> 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…

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.

Re: Why aren’t we talking more about airborne transmission?

#209

Post by nradov »

pjc50 wrote: post #150
jtbayly wrote: post #68

Earlier quoted context omitted.

> 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 take…

> 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.

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.

Re: Why aren’t we talking more about airborne transmission?

#210

Post by vict00ms »

jccooper wrote: post #109
elliekelly wrote: post #15

Earlier quoted context omitted.

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…

> Most big HVAC systems have this ability.

This is patently untrue.

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