Yes and no. I think large droplet transmission is easy to defend against in terms of hand washing, social distance, and masks. Aerosol, where it hangs in the air in a viable form for hours becomes difficult if you have classrooms with multiple occupants. Say you have a room that runs 5 classes throughout the day, with 13 people per class. Depending upon how well the ventilation is working - it‰??s possible that just 1 sick person per class breathing into that room and increasing virus count would make it so that by the end of the day it‰??s just not a safe situation for anybody teaching in that space, especially if they are there for an hour.

With droplets, it‰??s just a matter of distancing and cleaning surfaces and hands. Of course you can breath them in without distancing, but distance alone should help for the most part in that scenario.

So I agree, while it is just semantics in terms of what we are talking about, it has implications for re-opening strategies in terms of how things will be dealt with before, during, and after classes in any given space.

My major division here is just mass/size in that I‰??m assuming all droplets, regardless of size, fall quickly to the nearest horizontal surface where they rest until clean or whatever. Aerosols hover in the air for 3 hours or more, and can cause issues if inhaled.

Thanks for all of the replies. It‰??s been interesting. There is still a major divide when I look at those papers. Some (like the PNAS one) just simply use logic and smart speculation to make conclusions, while others (like the Nebraska study) actually measure a lot of data and try to see what is happening. With all of that, none of them have really shown that you can in fact get this by sitting in a restaurant far away from another person in the same room sharing the same air for over an hour. That for me is the major question. And it‰??s not for me personally, it is going to help guide decisions made by our University as to how we open and conduct business in the fall.

Take care

Dave

> On Jun 17, 2020, at 10:23 AM, Robin M. Izzo wrote:
>
> I think we get hung up on aerosol vs large droplet transmission. There is no doubt that SARS-CoV-2 spreads via large droplet transmission, which occurs even just from speaking, so "airborne transmission" may be both larger droplet and aerosol. How much of the transmission is from aerosol is the open question.
>
> ^^^^^^^^^^^^^^^^^^^^
> Robin M. Izzo, M.S.
> Executive Director
> Environmental Health and Safety
> 2020 Chair, ACS Division of Chemical Health and Safety
> Princeton University
> 262 Alexander Street
> Princeton, NJ 08544
> 609-258-6259 (office)
> 609-865-7156 (mobile)
> Please visit the EHS website at ehs.princeton.edu <http://ehs.princeton.edu/> and the Emergency Management website at emergency.princeton.edu <http://emergency.princeton.edu/>
>
> she/her/hers
>
>
>
> •ÈÀOn 6/17/20, 8:14 AM, "ACS Division of Chemical Health and Safety on behalf of Ralph Stuart" wrote:
>
>> 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.
>
> A new reference on this topic came out last week based on actual Covid epidemiological data. It is open access and can be found at:
>
> Identifying airborne transmission as the dominant route for the spread of COVID-19
> https://www.pnas.org/content/early/2020/06/10/2009637117
>
> The abstract is:
> Various mitigation measures have been implemented to fight the coronavirus disease 2019 (COVID-19) pandemic, including widely adopted social distancing and mandated face covering. However, assessing the effectiveness of those intervention practices hinges on the understanding of virus transmission, which remains uncertain. Here we show that airborne transmission is highly virulent and represents the dominant route to spread the disease.
>
> By analyzing the trend and mitigation measures in Wuhan, China, Italy, and New York City, from January 23 to May 9, 2020, we illustrate that the impacts of mitigation measures are discernable from the trends of the pandemic. Our analysis reveals that the difference with and without mandated face covering represents the determinant in shaping the pandemic trends in the three epicenters.
>
> This protective measure alone significantly reduced the number of infections, that is, by over 78,000 in Italy from April 6 to May 9 and over 66,000 in New York City from April 17 to May 9. Other mitigation measures, such as social distancing implemented in the United States, are in- sufficient by themselves in protecting the public. We conclude that wearing of face masks in public corresponds to the most effective means to prevent inter-human transmission, and this inexpensive practice, in conjunction with simultaneous social distancing, quarantine, and contact tracing, represents the most likely fighting opportunity to stop the COVID-19 pandemic. Our work also highlights the fact that sound science is essential in decision-making for the cur- rent and future public health pandemics.
>
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