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A staff member holds the door open for kids on the first day of school at Goodwin Frazier Elementary School in New Braunfels, Texas on Tuesday, Aug. 25, 2020. The number of Americans newly diagnosed with the coronavirus is falling — a development experts credit at least partly to increased wearing of masks — even as the outbreak continues to claim nearly 1,000 lives in the U.S. each day. (Mikala Compton/Herald-Zeitung via AP)

Q: What proof do scientists have that masks can actually prevent the spread of the coronavirus?

A: Singing, speaking, shouting, laughing, coughing and sneezing have been shown to discharge many large and small virus droplets capable of infection.

One experiment using high-speed video found that hundreds of droplets were generated when saying a simple phrase, but that nearly all these droplets were blocked when the mouth was covered by a damp washcloth. Several other studies have shown similar results.

An April 20 article in the journal Nature revealed wearing a surgical mask significantly reduced the amount of droplets and aerosols emitted from respiratory viruses. Case reports have shown infected persons wearing masks did not infect others despite several hours of close proximity.

Studies have revealed the viral load peaks days before symptoms begin and that speaking is enough to expel virus-carrying droplets. Epidemiologist George Rutherford, M.D., and infectious-disease specialist Peter Chin-Hong, M.D., both of the University of California, San Francisco, say the evidence shows that wearing a mask is vital since presymptomatic and asymptomatic transmission of COVID-19 is possible, making it impossible to know who is infected.

Asymptomatic carriers may not know they have the virus nor are capable of transmitting it, therefore placing everyone they contact at risk of infection. This reinforces the need for everyone to wear a mask and further supports the mask mandates in many counties, cities and states.

Research published in the Proceedings of the National Academy of Sciences concluded airborne transmission is the dominant route of spread for the coronavirus but that the number of infections could be reduced by this one protective measure alone. The results were determined by researchers in Texas and California, who compared COVID-19 infection rate trends in Italy and New York before and after face masks were made mandatory. Both locations started to see infection rates flatten only after mandatory face mask measures were put in place. Social distancing by itself was insufficient in protecting the public from the virus, but wearing face masks in public corresponded to the most effective means to prevent inter-human transmission. This inexpensive practice, in conjunction with simultaneous social distancing, quarantine and contact tracing, represents the most likely fighting opportunity to stop the pandemic.

The New England Journal of Medicine website includes video of the "Laser Light-Scattering Experiment Showing Speech-Generated Droplets." It revealed that large droplets fell to the ground, but small droplets can dehydrate and linger as "droplet nuclei" in the air and increase the area of transmission. Video clips of the events while the person was speaking, with and without a face mask, are available at https://www.nejm.org/doi/full/10.1056/nejmc2007800.

An Institute of Health Metrics and Evaluation has suggested that 33,000 deaths could be avoided by Oct. 1 if 95% of people wore masks in public.

— Susan Raschal, D.O., Covenant Allergy and Asthma Care; member, Chattanooga-Hamilton County Medical Society.

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Staff File Photo / Dr. Susan Raschal
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