Media Watch: Understanding the Risk of COVID-19 Transmission Indoors

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cubicles As businesses begin to reopen cautiously across the country people must weigh the risk of returning to these enclosed spaces amid the pandemic. Research is beginning to indicate that maintaining physical distancing and limiting time spent in large groups and wearing a mask can help to reduce the spread of COVID-19 outdoors. But whether these procedures will result in the same protection inside, remains in question.

Environmental engineering researchers from Drexel University’s College of Engineering have provided insight on what is known about airborne viral transmission indoors and, importantly, what questions must be answered as people consider gathering in places other than their homes for the first time in months.

Charles Haas, PhD, LD Betz professor of Environmental Engineering in the College, who is a leading mind in understanding and assessing how toxins and pathogens are spread in various environments, published an editorial in April in the journal The Society for Risk Assessment, outlining strategies for gauging and communicating about coronavirus transmission risk. Since then he has engaged media to help the public better understand what is and isn’t known and what can be reasonably inferred about how the coronavirus is transmitted in the air.

In a late April Axios interview, Haas underscored the importance of public officials communicating the uncertainty surrounding COVID-19, as a way of establishing trust an enabling the public to make an educated judgment about risk.

“A key message is you can never get to zero with anything when it comes to risk.”

Haas reiterated this message in a May 25 Vox story about the various factors that affect COVID-19 transmission indoors. In the piece, entitled “6 feet away isn’t enough. Covid-19 risk involves other dimensions, too,” Haas explains that reducing airborne transmission risk is a combination of distancing, avoiding enclosed areas and large groups and limiting the time of direct contact with others.

The risk of catching the coronavirus, simply put, “is breathing in everybody’s breath,” says Charles Haas, an environmental engineer at Drexel University. Droplets fly from people’s mouths and noses when they breathe, talk, or sneeze. Other people can breathe them in. That’s the main risk, and that’s why face masks are an essential precaution (they help stop the droplets from spewing far from a person’s mouth or nose).

His input on airborne spread of the virus was also cited in a Vox story about more than 100 worshippers contracting the coronavirus at a single worship service in Germany and a Wall Street Journal piece about how airlines are trying to understand and mitigate viral transmission in airplanes.

The CDC has said the virus appears primarily to spread person to person within about 6 feet through droplets excreted by coughing, sneezing or talking. Charles Haas, a professor of environmental engineering at Drexel University, said more research is needed to know whether airborne particles in aircraft or other indoor spaces could spread the virus beyond such a limited area.

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Haas’ colleague in the Department of Civil, Architectural and Environmental Engineering, L. James Lo, PhD, has also provided expert insight on indoor air systems and how they could be adjusted to reduce the risk of transmission.

Lo was recently quoted in The Washington Post in a story about how restaurants can safely welcome people to dine in again. His insights explain the importance of increasing ventilation to prevent the virus from lingering in the air and accumulating inside restaurants.

How the virus is transmitted might be more important in restaurants than in many other venues, notes L. James Lo, an assistant professor at Drexel University in Philadelphia who studies airflow and how viruses circulate, because people linger there far longer than they do in, say, a grocery store. Exposure to the virus can come from encountering a high dose for a short time or a low dose over a longer period, he says.

“In a restaurant, you’re enjoying your dinner and spending more time, which means you are stuck with the same people for a long time.”

As people consider returning to restaurants for more than takeout, Lo suggests outdoor seating could be one way to lower the risk of airborne transmission of the virus.

Completely open-air dining is safest; covered patios are better than indoors, Lo says. “The more obstruction for natural air movement, the less flushed-out the air is going to be,” he says.


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