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What do I need to know about possible “aerosol-based” COVID transmission?

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There has been a lot of discussion recently regarding whether COVID-19 is regularly transmitted via aerosols (small particles <5 microns in diameter that can hover in the air for hours) vs. droplets (larger particles that are believed to drop to the ground within 6 feet of being generated, though some more recent studies have shown even these larger particles can travel up to >20 feet in some settings). While we know COVID can be transmitted via aerosols during procedures such as intubation or mechanical ventilation (i.e. in an ICU setting), some anecdotal reports have recently suggested aerosol-based transmission may be occurring in more common indoor settings (examples include several members of a choir becoming infected, as well as a large percentage of workers in a small call center).  

We are still trying to more definitively answer the question of how large a role aerosol-based transmission is playing in COVID-19. Most experts believe it probably plays some role, but not a large part. If aerosol-based transmission played a large role, we would expect a larger number of people to be infected from each infected person (more like measles, which has an R naught of 18, compared to COVID-19’s of around 2-3) and we would expect N95 masks, made to prevent passage of smaller particles, to prevent more infections than surgical masks in the hospital setting (but studies have not convincingly demonstrated this). It would have made it less likely that countries which employed early universal masking policies (using surgical and cloth masks) would have so effectively curbed their infection rates as they did. 

The answer to how large a role aerosol-based transmission plays in COVID-19 transmission will help guide prevention strategies. Aerosolized particles can build up in the air in unventilated, indoor areas and potentially infect someone passing through hours later. Because we do believe this is playing at least a minor role in transmission, it is a good idea, until we know more, to minimize time spent in indoor communal settings without good ventilation.

For more information, an article written by Chanu Rhee, a colleague of Dr. Abrams’ from her Stanford Internal Medicine residency, now an epidemiologist and infectious disease physician at Harvard’s Brigham & Women’s Hospital, wrote this helpful piece published in JAMA.