Scientists call for better public health guidance about how coronavirus spreads in air

Scientists have published an open letter calling for public health officials to make a clear distinction between the spread of the novel coronavirus via droplets ejected by coughing or sneezing, and from aerosols that can carry the virus for much greater distances.

The researchers, including those from the University of California (UC) San Diego and the University of Maryland in the US, called for the scientific community to clarify the terminology used related to aerosols and droplets, and employ a more modern size threshold, rather than the existing one which is based on 1930s-era work.

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Viruses in aerosols smaller than 100 microns can remain airborne in a confined space for prolonged periods of time, and accumulate in poorly ventilated air, leading to transmission, they wrote in the letter, published in the journal Science.

"The balance of attention must be shifted to protecting against airborne transmission," said the group, led by Kimberly Prather from UC San Diego.

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Viruses in aerosols can remain suspended in air for many seconds to hours, like smoke, and be inhaled, the scientists noted in the letter.

"They are highly concentrated near an infected person, so they can infect people most easily in close proximity. But aerosols containing infectious virus can also travel more than two metres and accumulate in poorly ventilated indoor air, leading to superspreading events," the researchers noted.

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In addition to mask wearing, social distancing and hygiene efforts, they urged for public health officials to articulate the importance of moving activities outdoors, improving indoor air using ventilation and filtration, and improving protection for high risk workers.

"The goal of this letter is to make it clear that the SARS-CoV-2 virus travels in the air and people can become infected via inhalation," Prather said.

"It is important to acknowledge this pathway so efforts can focus on cleaning the air and providing guidance on how to avoid risky indoor settings," he added.

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According to the scientists, it is important for people to wear masks at all times in public buildings and confined spaces, not only when they can't maintain social distance.

"This isn't just an academic question, but a point that will help reduce transmission if public health officials offer clear and forceful guidance about this," said Linsey Marr, a co-author of the letter from Virginia Tech in the US.