Does air conditioning spread the coronavirus?

The question comes as states are allowing indoor businesses to reopen, as well as allowing increasingly large gatherings of people.

COVID-19 cases are spiking across Southern and Western states just as rising summer temperatures are drawing people indoors to seek relief in the air conditioning. But can air conditioning facilitate the spread of the coronavirus?

The question comes as states are allowing indoor businesses to reopen, as well as allow increasingly large gatherings of people. But concerns about air conditioning are making their way into reopening policies in some states.

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“There’s some reports that malls, bars, certain social clubs with air conditioning, that air conditioning may not be cleansing the air of the virus, just recirculating the air with the virus.” New York Gov. Andrew Cuomo said in a briefing Wednesday. Malls and gyms will not be a part of New York’s phase four reopening because of this concern.

But experts say there’s little evidence to link air conditioning to the spread of the coronavirus. Rather, the risk more likely comes from the amount of time spent indoors in close proximity to others.

“The opening up of facilities from my point of view, and I think this is shared by colleagues, that doesn't depend on the air conditioning, it's the gathering of the people for long periods of time,” said Dr. William Schaffner, a professor of preventive medicine and infectious diseases at the Vanderbilt University Medical Center.

“You can think of laboratory experiments and theoretical possibilities of how air conditioning might spread this virus, but so far, there really isn't any noteworthy evidence that this is happening,” he said.

A study published in April raised concerns that air conditioning could spread the coronavirus. The research, published in the Centers for Disease Control and Prevention’s Emerging Infectious Diseases journal, detailed an instance in which 10 restaurantgoers in China were sickened after eating at neighboring tables. The authors concluded that the virus was spread by the air conditioning system blowing tiny virus-laden droplets through the air.

Schaffner said this study may be an interesting outlier, but noted that there have been no further stories like this documented with the millions of infections worldwide.

Dr. Amesh Adalja, an infectious disease physician and a senior scholar at the Johns Hopkins Center for Health Security, agreed.

“I haven't seen any strong evidence that we're seeing that this is transmitted in an airborne manner,” he said. “This is primarily spreading from droplets that go from one person directly to another person.”

While it’s theoretically possible that air conditioning can facilitate the spread of the virus, a lot of factors would have to align for that to happen, such as the timing of a cough or a gush of air at the right moment, Joseph Fair, a virologist and a NBC News contributor, said.

Spread through air conditioning isn’t a major factor in transmission, as the numbers don’t reflect that, he said.

“If you think about how many Americans use AC, it's 9 out of 10 of us, so we'd have a lot more [cases] than what we have right now,” Fair said.

With proper ventilation, coronavirus transmission shouldn’t be an issue, said Bill Bahnfleth, a professor of architectural engineering at the Penn State Institutes of Energy and the Environment. In the instance where the virus may have spread in a restaurant, the ventilation didn’t meet the standards used in the U.S., he said.

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“If you had ventilation at what I would consider a normal or appropriate level, the concentration may have never been high enough for any of those people to receive an infectious dose over the hour and a half that they were in the same place,” said Bahnfleth, who is also a member of the American Society of Heating, Refrigerating and Air-Conditioning Engineers.

According to a statement in April from that group, heating, ventilation and air conditioning can actually slow the spread of the virus.

“Ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air,” the statement said. “In general, disabling of heating, ventilating, and air-conditioning systems is not a recommended measure to reduce the transmission of the virus.”