By Steven Reinberg
WEDNESDAY, Sept. 23, 2020 (HealthDay News) -- If you sing indoors without a face mask, you run the risk of spreading COVID-19 through tiny airborne particles known as aerosols.
That's the conclusion researchers reached after studying a choir practice.
In Skagit Valley, Wash., one person with mild symptoms of COVID-19 attended a 2.5-hour-long indoor choir practice on March 10. Over the next several weeks, more than 50 others from the rehearsal got sick and two died.
"This study documents in great detail that the only plausible explanation for this super-spreading event was transmission by aerosols," said lead author Shelly Miller, a professor of mechanical engineering at the University of Colorado Boulder. "Shared air is important because you can be inhaling what someone else exhaled even if they are far away from you."
The singers did not touch each other or shared surfaces, and few used the same restroom as the infected person. But they did not wear masks.
Poor ventilation led aerosols and heat from the singers' to mix with room air, the researchers noted in a university news release.
According to study co-author Jose-Luis Jimenez, "The inhalation of infectious respiratory aerosol from 'shared air' was the leading mode of transmission." Jimenez is a professor of chemistry and fellow at the Cooperative Institute for Research in Environmental Sciences, at the university.
The researchers estimated that shortening the rehearsal to 30 minutes would have reduced the infection rate from 87% to 12%. If masks had been worn, the number of people infected would have dropped from 52 to five, they added.
Miller pointed out that "singing is known to release high amounts of aerosol."
Jimenez said that "the research adds to the overwhelming body of evidence that aerosol transmission is playing a major role in driving the pandemic and especially in super-spreading events."
The findings were published Sept. 18 in the journal Indoor Air.