"How long diseases like measles and the flu linger in the air — after an infected person has left the room"

[ojelabii@norden.social]

@DenisCOVIDinfoguy »[…] and build up indoors even after an infected person leaves.« Build up? How can they, the viruses at least, “build up”?

[kanamauna@sauropods.win]

@mikemccaffrey @DenisCOVIDinfoguy

From what I've read, it is a fairly tough microbe that can survive dry environments for surprisingly long periods. The other ones on the list are probably inactive before they hit the ground.

[drangnon@hachyderm.io]

@DenisCOVIDinfoguy instead of just accepting these numbers, get air purifiers for spaces you control, and push the owners of space you don't control to do it too

[fedithing@social.chinwag.org]

@DenisCOVIDinfoguy

Best weapon against this is masking plus keeping windows open, preferably windows on different sides of the room so that there's a draught flowing through. If you only have one window you can use an electric fan next to it to create a draught.

The room's air exchanges several times more quickly if you have a good draught of some kind. I can't find it now, but Japanese researchers did an excellent video illustrating this with smoke machines and lasers.

If you get a good quality CO2 meter you can actually watch the air get fresher as the numbers drop.

[su_g@aus.social]

@DenisCOVIDinfoguy
A handy reference - thank you! That tuberculosis is a real outlier - I’m reading about some resurgence in the US, not good. ️

[cy@pdx.social]

@mikemccaffrey @DenisCOVIDinfoguy @KanaMauna Seems sketchy to me. Is this one of those "only in a carefully controlled lab environment in total darkness" things?

I know the COVID scare had the researchers protesting (and being ignored) that it breaks down quickly in sunlight.

[datum@zeroes.ca]

@DenisCOVIDinfoguy Ok but the paper they link does NOT say "up to 3 hours" for COVID-19, it says aerosolized COVID-19 is still highly infectious after 3 hours, when they stopped testing

SARS-CoV-2 remained viable in aerosols throughout the duration of our experiment (3 hours), with a reduction in infectious titer from 10^3.5 to 10^2.7 TCID50 per liter of air New England Journal of Medicine

in other words after 3 hours, every single liter of air contained HUNDREDS of particles that could infect.

And in the years since the 2020 study they cite, others have looked at longer time scales, and papers have found that in indoor air > 500 ppm CO2, enough infectious particles effectively persist indefinitely that cleaning the air is the only physically plausible approach: Nature

#COVID19 #COVID #SARSCoV2 #COVIDisAirborne #PublicHealth #pandemic #CovidIsNotOver

[jmcrookston@mastodon.social]

@datum

Agree. Three hours would be short. It's going to be a statistical distribution as the virus particles over time are rendered non-viable, with long tail. They probably last a lot longer in the air than we'd care to admit to ourselves. Coronas in experimental rotating drums lasted 48 hours or something. That said, the particles dilute over time, and we need to breathe enough that one particle does end up infecting.

[jmcrookston@mastodon.social]

@datum I'd only trust any of those studies if done by knowledgeable people (they never are) and with a suitable sample size (they're usually done by ID people and they're embarrassingly bad). Hope the studies that produced these numbers were decent.

[lkdc@dmv.community]

@jmcrookston @datum I'm trying to understand what all this means, in practical terms, for covid-cautious people who live with people who take no covid precautions. A common concern is removing one's respirator to take a shower in a bathroom that has recently been used by someone who might be infected with SARS-CoV-2. I've been under the impression that there's value in waiting even a short time (15-60 minutes), as the risk will go down, albeit not to zero. Is that incorrect?

[datum@zeroes.ca]

@jmcrookston Yep. The newer article I linked splits infectivity into phases, and in the final phase volume has decreased to the point that mucin effectively stops evaporation, and SARS-CoV-2 degrades very slowly if there's no UV.

"The particles dilute over time" so long as there's any ACH. I had a discussion here where someone pointed out their shared stairwell has effectively no ventilation, at which point it's deposition rate. Slow!

[datum@zeroes.ca]

@Lkdc so I suggest figure 6 from https://www.nature.com/articles/s41467-024-47777-5

Yes, waiting a short time would reduce airborne load.

It would also help to open a window - both for ACH and because lower CO2 speeds viable virus degradation.

The long tail hard to avoid. If the bathroom is ventilated to 3 ACH it's not "the air is completely gone 3x an hour" but "thrice the volume of air in the room is exchanged per hour" and so forth.

If it's a scenario you face, you could consider augmenting whatever ventilation the common bathroom has with UV disinfection, since it's likely much easier to plug in an emitter than to upgrade ventilation.

I believe there's a correlation between inoculum dose and negative outcomes.

So yes I would understand waiting until the first two phases are expected to pass if possible (their durations can be estimated from that paper and checking humidity (RH) and CO2), and then ACH or UV sterilization to bring down the long tail until it's within your risk budget.

[datum@zeroes.ca]

@Lkdc Also a thought experiment:

there is a point at which a person, infected with SARS2, hasn't yet exhaled an infectious particle.

And so there is a point at which they're still are producing very few per exhalation.

Then at the other extreme are superspreaders, putting thousands of infectious particles into the air per exhalation.

While some degrees of defense (waiting 15-60 minutes) are unlikely to be reliable against the latter, they could well bring the former down to astronomical odds of transmission.

So maybe the most honest answer is "whether waiting 15-60 minutes is enough to prevent infection varies, but it will only ever help."

[lkdc@dmv.community]

@datum Thank you very much for the detailed assessment.

[jmcrookston@mastodon.social]

@datum yes if ventilation I meant. Which can be slow or fast of course. If nothing then yes it's agglutination (I understand the particles tend toward certain sizes) and deposition on walls and ceiling and floor. Like cigarette smoke. Should hang out for a long while.

If people want to know how long they can just burn some toast on a pan. Then they can tell us how long that smoke hangs out

If they really want to be bright, they could run their air purifier and see how quickly it clears the air

[scienceisnotopinions@mstdn.ca]

@datum I would like to hear some information about how contagious this virus is outdoors playing sports with people.

I've had to give up five years of pickelball becasue of this virus.

[nilajones@zeroes.ca]

@datum @Lkdc

As an easy approximation, I would say run the ceiling fan if you have one, or put a fan in the window, and run it until the air doesn't seem steamy to you anymore, the mirror is not steamed up, etc.

Then you can figure the air has been changed

This will probably take 30-45 minutes

Also, I keep my mask on when taking a bath. So that's an option, if you have a tub

[dianea@lgbtqia.space]

@DenisCOVIDinfoguy

From my own no-covid experience since this started, wearing a kn-95 mask as fit tested at all times is good enough. If someone sneezes or coughs in the room, absolutely keep that mask on.

[nilajones@zeroes.ca]

@Scienceisnotopinions @datum

The only two times I've caught symptomatic covid, I was outdoors, socially distanced, and wearing an n95. But the other person wasn't

So I wouldn't play pickleball with unmasked people

[nilajones@zeroes.ca]

@Su_G @DenisCOVIDinfoguy

Problem is, it's not an outlier. People are posting links to papers, in the thread. Covid is never gone, until fresh air has replaced all the air in the room. Certainly not gone in 3 hours

This also makes me question all the other numbers