>A recent article in the Journal of Occupational and Environmental Hygiene (July 2020) reports that the routes of transmission to healthcare personnel from COVID-19 infected patients is predominated by inhalation (57%) and droplets (35%) compared to contact routes (8.2%).
Thanks for pointing out this very interesting article. I would note that there is no original field data associated with those numbers, as is true of many of the studies of Covid transmission being published these days. For this reason, I suspect that the number of significant figures listed above are over-precise.
I also find the use of a single number to represent the impact of ventilation in the model overly-simplistic (the author quotes ASHRAE as saying between 6 and 12 air changes per hour, which is quite high compared to non-lab settings). Directionality of air flow has been implicated in many super-spreader events and higher air flow rates could increase spread of the virus in those events.
It's also not clear to me that the healthcare setting is a good environment to represent other locations. Health care settings have a good idea of who is infectious and strong infection control cultures compared to areas that the public is allowed into routinely. Controlling virus emitted from random individuals in a heterogeneous environment is a different challenge than that faced by the health care professionals.
However, I agree with the authors observation that
"Clarification of the emission and infectivity of SARS-CoV-2 at different sites in the respiratory tract is necessary to improve our understanding of the contribution of contact, droplet, and inhalation routes of COVID-19 transmission."
Ralph Stuart, CIH, CCHO
Environmental Safety Manager
Keene State College
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