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Previous by Date: Subject: Re: [DCHAS-L] COVID19 spread question Date: Tuesday, June 16, 2020 at 1:48:41 PM Author: Zack Mansdorf <mansdorfz**At_Symbol_Here**BELLSOUTH.NET>

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This Italian article proposes a model for infection indoors based on ventilation. It explores different scenarios like grocery stores and pharmacies.

Estimation of airborne viral emission: Quanta emission rate of SARS-CoV-2 for infection risk assessment
https://www.sciencedirect.com/science/article/pii/S0160412020312800

Thank you,

Yaritza Brinker
260.827.5402

-----Original Message-----
From: ACS Division of Chemical Health and Safety On Behalf Of Zack Mansdorf
Sent: Tuesday, June 16, 2020 1:49 PM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: Re: [DCHAS-L] COVID19 spread question

** External Email **

Great question. I believe that the only test for viable virus has been done by the hugely sophisticated National Biodefense Analysis and Countermeasures Center at Fort Detrick. This high security level 4 biosafety lab can measure live (active would be a better term) corona virus in air. All the other tests (PCR) measurements can include viral fragments (meaning the virus might not be infective/viable). This is why fragments have been found for long periods of time on fomites (days) and in very small aerosols. At the same time, we do not know the infective dose or the minimally infective dose although there has been speculation about it based on other like virus (maybe 100 or more units).

Bottom line-we do not know and can only speculate. As to aerosols, this is just aerosol physics and airflow to calculate the Stokes Settling Velocity.

Since one can only speculate, I would suspect it is highly unlikely that air suspensions of human aerosols inside for more than a few minutes would be likely (my speculation). Otherwise, do not ever enter any elevator or hospital room or any other closed space where there is not a very strong air current. Here is the good news. The Fort Detrick lab clearly showed that sunlight (UV) very quickly degrades the virus (half-life of <2 minutes). In my neck of the woods (South Florida), I am guessing seconds in the outside air on a normal day.

I think we will get an answer soon (maybe from Fort Detrick), but in the meantime is it interesting to speculate on what we do know.

Zack Mansdorf

-----Original Message-----
From: ACS Division of Chemical Health and Safety On Behalf Of David Roberts
Sent: Tuesday, June 16, 2020 8:58 AM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: [DCHAS-L] COVID19 spread question

Hello,

OK - I know where this might go, but I‰??m asking that people give nice, honest answers here and don‰??t judge or rant. I honestly need somebody to tell me why we all are saying that we need to worry about aerosol transmission when it comes to Covid-19. My friend worked at the CDC, and is quite knowledgeable on the subject. She was in Africa during the first Ebola crisis, and knows a bit about transmission and such. She feels that it‰??s truly just a droplet transmission thing (big difference - one can be mitigated by social distancing, the other needs to deal with room ventilation considerations).

I need evidence stating that somebody has done the experiment on room air to show that the virus is in the air for 3 hours, and it increases over time if you have somebody infected sitting and breathing in the room. Does anybody have a paper on this that isn‰??t one of assumption and conjecture but has actual data with measurements.

Are we all saying aerosol when we mean droplets? The CDC website only says droplets - there is no indication that aerosol transmission is a viable way for this virus to transmit, according to the CDC.

My friend has a theory that if it was truly an aerosol transmission that we would see way more cases. Doesn‰??t think the virus can live in an aerosol - thinks it may dry up and become non-viable.

I see two different things when I read online about what you need to worry about. One is saying it‰??s aerosolized and lives 3 hours in air - that‰??s what she is questioning. Why do we say this? Is that from a 1950s reference or is there real evidence here for this situation??? The other is droplet transmission, which I feel is a true threat and worry with this virus. Droplet transmission can be easily mitigated by social distance, hygiene, and mask wearing. Droplets have some mass and thus don‰??t really float around in the air so much. Aerosol is much more difficult and scary.

Thanks.

Dave

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