General Information

2020 Lester Andrews Graduate Research Symposium

Due to COVID, Dr. Bax’s presentation was postponed to Oct. 23, 2020.

What we know and don’t know about the role of droplets and aerosol in transmission of SARS-CoV-2

Abstract: Transmission of respiratory diseases by droplets has been studied for over a century and definitive knowledge was summarized by Wells in 1955 [1] but seems to have long been forgotten. Of the various types of respiratory droplets, which include breathing, speaking, coughing, and sneezing, the latter two are most widely recognized as they relate directly to symptoms. By default, speech and/or breathing droplets are strongly implicated in the now well-established importance of SARS-CoV-2 transmission by disease carriers without symptoms. Laser light scattering shows that breathing droplets are highly abundant but mostly sub-micron in size. The physical mechanism by which the various types and quantities of droplets are generated can yield a better understanding of their infectivity in relation to the disease state of the emitter. Rapid evaporation of their aqueous fraction transforms smaller droplets (< ~50 microns) into aerosol prior to reaching ground, and their distance traveled is then dominated by air convection. Their rapid volume shrinkage by up to 100-fold presents a major challenge in limiting their spread, but also an opportunity in blocking them prior to evaporation. Simple light scattering measurements are illustrated that can visualize and quantify droplet nuclei spanning more than 4 orders of magnitude in volume.

[1] W.F. Wells, Airborne Contagion and Air Hygiene: An Ecological Study of Droplet Infections. Harvard University Press, Cambridge, 1955.