Why isn't increasing ventilation of public spaces part of the best practice response to the Coronovirus?
post by ChristianKl · 2020-03-12T10:40:47.502Z · LW · GW · 2 commentsThis is a question post.
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Answers 5 Spiracular 5 Spiracular 4 brianwang712 None 2 comments
It's my impression that there's some spread via aerosol in public spaces like buses and trains. By increasing ventilation in those spaces by opening more windows I find it plausible that we could reduce that transmission.
Why aren't health orgs pushing for increasing ventilation of public spaces?
Answers
Boy, it's been quite a while! Have a half-assed conclusion (/retrospective/answer).
Here's an article with a lot of illustrations whose models suggest that increased ventilation (in several common scenarios) results in a reduction in infection rate by a factor of about 5-7x, even when compared to mask wearing.
https://www.microcovid.org/ 's model seems to be using a 5x reduction number for indoor vs "almost-outdoor," which seems to roughly line up with this.
For comparison, mCov's factor-reductions for surgical-mask wearing are 2x, and n95s are 10x. So "open-windows and heavy ventilation" lands basically right between the two in reducing risk.
My impression at this point is that adequate ventilation was a pretty strong target for reducing spread.
So... Kudos or BayesPoints to ChristianKI (whichever you prefer) for calling that 8 months ago.
Here's a paper on SARS-1 that seems highly-relevant:
Role of air distribution in SARS transmission during the largest nosocomial outbreak in Hong Kong.
Our study revealed the need for the development of improved ventilation and air-conditioning systems in an isolation ward or a general hospital ward for infectious respiratory diseases. The outbreak in Ward 8A, which was in a general hospital and could house nearly 40 patients, demonstrated the cross-infection risks of respiratory infectious diseases in hospitals if a potential highly infectious patient was not identified and isolated. Our example simulation, which extended the SARS Busters' design for an isolation room to Ward 8A, demonstrated that there was room for improvement to minimize cross-infection in large general hospital wards.
↑ comment by Spiracular · 2020-03-18T00:53:43.081Z · LW(p) · GW(p)
I have not read through all of it yet, but even the abstract seems to suggest that someone agrees with you, thinks it contributed to that outbreak, and has at least started looking into it.
I'm not sure how extensive the suggested edits were, but I do have to comment that in all likelihood, sporadic crisis-based funding is not conductive to altering the ventilation architecture of a large fraction of hospitals.
(It has been my weak impression that pandemic-related funding has historically relied heavily on a tiny handful of interested politicians and on taking full advantage of policy-windows whenever there's an outbreak or a scare.)
If there is a good argument that a ventilation redesign would help prevent pneumonia or other common hospital-acquired-infections, I suspect that would be a good thing to look into and add to the proposal. If true, it would make the argument a lot stronger, and also likelier to get implemented and upkept.
↑ comment by Raemon · 2020-03-18T00:41:42.555Z · LW(p) · GW(p)
Abstract:
SARS is primarily transmitted by bio-aerosol droplets or direct personal contacts. We present a study of environmental evidence of possible airborne transmission in a hospital ward during the largest nosocomial SARS outbreak in Hong Kong in March 2003.
Retrospective on-site inspections and measurements of the ventilation design and air distribution system were carried out on July 17, 2003. Limited on-site measurements of bio-aerosol dispersion were also carried out on July 22. Computational fluid dynamics simulations were performed to analyze the bio-aerosol dispersion in the hospital ward. We attempted to predict the air distribution during the time of measurement in July 2003 and the time of exposure in March 2003.
The predicted bio-aerosol concentration distribution in the ward seemed to agree fairly well with the spatial infection pattern of SARS cases. Possible improvement to air distribution in the hospital ward was also considered.
PRACTICAL IMPLICATIONS:
Our study revealed the need for the development of improved ventilation and air-conditioning systems in an isolation ward or a general hospital ward for infectious respiratory diseases. The outbreak in Ward 8A, which was in a general hospital and could house nearly 40 patients, demonstrated the cross-infection risks of respiratory infectious diseases in hospitals if a potential highly infectious patient was not identified and isolated. Our example simulation, which extended the SARS Busters' design for an isolation room to Ward 8A, demonstrated that there was room for improvement to minimize cross-infection in large general hospital wards.
Here's a good op-ed on this topic: https://www.nytimes.com/2020/03/04/opinion/coronavirus-buildings.html
The author suggests that the lack of attention on building ventilation is due to uncertainty about how important close contact (i.e., close enough that a person's respiratory droplets could directly land on you) is for transmission, vs. more indirect airborne transmission.
(E.g., from CDC website: "Early reports suggest person-to-person transmission most commonly happens during close exposure to a person infected with COVID-19, primarily via respiratory droplets produced when the infected person coughs or sneezes. Droplets can land in the mouths, noses, or eyes of people who are nearby or possibly be inhaled into the lungs of those within close proximity. The contribution of small respirable particles, sometimes called aerosols or droplet nuclei, to close proximity transmission is currently uncertain. However, airborne transmission from person-to-person over long distances is unlikely.")
↑ comment by ChristianKl · 2020-03-12T12:36:57.642Z · LW(p) · GW(p)
It seems to me like this is a potential dangerous error given that paper about the bus where people got infected despite having some distance.
Replies from: habryka4↑ comment by habryka (habryka4) · 2020-03-12T19:05:08.543Z · LW(p) · GW(p)
Note that that paper was retracted for unclear reasons. So unsure how much we should weigh it.
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comment by Spiracular · 2020-03-16T22:05:56.187Z · LW(p) · GW(p)
Not an answer, but fwiw, my impression is that there's reasonable odds of at least some aerosol transmission, not just large droplets when coughing. Although I concede that close-contact during symptomatic periods (or a few days before/after) is probably the primary transmission mechanism, especially given how much it seems to circulate in families.
CIDRAP mentions that we don't know that 6 feet is sufficient, and that aerosol transmission has been seen in MERS (a different coronavirus).
This preprint on surface survival mentioned that SARS-CoV-2 (which they called HCoV-19) seemed able to survive in an aerosol for several hours and remained viable (although also note gwillen's comment [LW(p) · GW(p)] on this.)
This seems like a reasonable question, especially given the extent to which we've seen cruise ships (where adequate ventilation is apparently challenging) get incredibly infected.
comment by PeterMcCluskey · 2020-04-20T02:04:40.642Z · LW(p) · GW(p)
I initially guessed ventilation would only provide minor benefits. But I've decided now that it looks medium to high value.
I've been influenced in part by this Stat article and this J Storrs Hall blog post.