“Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering,” Philip Anfinrud, Valentyn Stadnytskyi, Christina E. Bax, and Adriaan Bax, New England Journal of Medicine, April 15, 2020. (Thanks to Andrea DeMeter for bringing this to our attention.) The authors, at the National Institutes of Health and the University of Pennsylvania, report:
Aerosols and droplets generated during speech have been implicated in the person-to-person transmission of viruses, and there is current interest in understanding the mechanisms responsible for the spread of Covid-19 by these means. The act of speaking generates oral fluid droplets that vary widely in size, and these droplets can harbor infectious virus particles….
We report the results of a laser light-scattering experiment in which speech-generated droplets and their trajectories were visualized. We found that when the person said “stay healthy,” numerous droplets ranging from 20 to 500 μm were generated….
We found that when the person said “stay healthy,” numerous droplets ranging from 20 to 500 μm were generated…. When the same phrase was uttered three times through a slightly damp washcloth over the speaker’s mouth, the flash count remained close to the background level (mean, 0.1 flashes); this showed a decrease in the number of forward-moving droplets.
BONUS: The COVID-19 pandemic is producing bizarre adventures for biomedical professionals. The New England Journal of Medicine has a letter from one of them:
Our supply-chain group has worked around the clock to secure gowns, gloves, face masks, goggles, face shields, and N95 respirators… Before we could send the funds by wire transfer, two Federal Bureau of Investigation agents arrived, showed their badges, and started questioning me. No, this shipment was not headed for resale or the black market. The agents checked my credentials, and I tried to convince them that the shipment of PPE was bound for hospitals. After receiving my assurances and hearing about our health system’s urgent needs, the agents let the boxes of equipment be released and loaded into the trucks. But I was soon shocked to learn that the Department of Homeland Security was still considering redirecting our PPE. Only some quick calls leading to intervention by our congressional representative prevented its seizure. I remained nervous and worried on the long drive back, feelings that did not abate until midnight, when I received the call that the PPE shipment was secured at our warehouse.
This experience might have made for an entertaining tale at a cocktail party, had the success of our mission not been so critical.