Air conditioners could be aiding the spread of COVID-19 indoors, epidemiologists say

LOS ANGELES -- Amid record-breaking temperatures across the country, people are cranking up their air conditioners to beat the heat. But some researchers are saying that air conditioning in public indoor spaces could actually be causing the coronavirus to spread.

Some experts were hopeful that the summer heat would dissipate the COVID-19 virus and provide a brief period of relief, but Dr. William Hanage, an epidemiologist professor at Harvard University, said that COVID-19 is not significantly affected by the change in the seasons.

“People like me have known that transmission was not going to go away in the heat for some time, months, since the winter. We just didn’t know how big the impact would be,” Hanage said.

In fact, some experts now believe the heat may be having an exacerbating effect on the spread of the virus, as many people are being driven indoors in order to cool down. Edward Nardell, a professor at Harvard Medical School and an infectious disease expert, suggested Friday that air conditioning use across the southern U.S. may be a factor in spiking COVID-19 cases.

“It is, but not necessarily for the ways you’re thinking,” Nardell pointed out. “Because of air conditioning and excessive heat, people are indoors and re-breathing each other’s air.”

Nardell presented data which surveyed places in countries that had the biggest increases in COVID-19 over time. “The places that had the need for most air conditioning, have had the biggest increases in COVID,” Nardell said. But Nardell noted that the data could have other correlates, and did not necessarily imply causation.

According to Hanage, the risk of transmission of the novel coronavirus is higher indoors.

A recent study by the University of Maryland (UMD) showed that some air conditioning units could spread the virus, according to Don Milton, a professor of environmental health at UMD. His findings, which were published by the university’s School of Public Health, suggested that air conditioning can blow around infected droplets hanging in the air.

“Outbreaks — where you have a bunch of people infected all at once like that — are almost exclusively occurring indoors in poorly ventilated environments," Milton explained.

It’s yet another COVID-19 worry, as people try to stay indoors to get away from scorching hot weather. So, what can people do?

Joseph Allen, an assistant professor of exposure assessment science at the Harvard T.H. Chan School of Public Health and director of its Healthy Buildings program, suspects that airborne transmission of COVID-19 is likely, according to a recent interview with The Harvard Gazette.

He said a portable air purifier to filter out airborne particles or a portable humidifier should help. In mechanically ventilated building systems, Allen said almost all of them recirculate some amount of air. The recirculation causes emitting aerosols to be picked up and transported to other areas in a building.

“One way to cut that off when you have a recirculated air supply is to have high-efficiency filters, or certainly upgraded filters from what is typically in a building, which will only capture a small percent of viral particles,” Allen said.

Allen said high-efficiency filters do a much better job at limiting transmission from room to room.

If you don’t have a central air system, Allen suggested opening up your windows as much as you can. “You want to make sure that if you are recirculating air, that it’s being filtered through upgraded filters.” He added, “HEPA filters capture 99.97 percent of particles, so upgraded filters can be effective.”

But Nardell said nothing is foolproof. “We’re always talking probability. So we can lower the probability infection with air disinfection.”

Nardel said airborne infection is a problem in public buildings, where someone may have COVID-19. Disinfection techniques include UV lights, room air cleaners and increased ventilation.

Nardell said that ultraviolet lights may also be able to sterilize the air of COVID-19. Ultraviolet, germicidal lamps have been proven effective in protecting against tuberculosis infection and are already in use in some settings to fight SARS-CoV-2, according to Nardell. The lamps shine horizontally, where sterilization is required. Air currents circulate up to the ceiling, where the UV light kills the pathogens.

Evidence has mounted that some cases of COVID-19 occur through airborne transmission. According to Mount Sinai Hospital’s Department of Microbiology, airborne transmission refers to situations where residue from droplets remain suspended in the air for long periods of time. These organisms can survive long periods of time outside the body.

“Often, the term ‘airborne transmission’ creates panic because people imagine these clouds of virus roaming around the streets coming after them. But that’s not the way it works,” Dr. Linsey Marr, a professor at Virginia Tech with expertise in airborne transmission of viruses and air quality said. “The concern is greatest when you are close to a person who happens to be infected, if they’re talking, especially if you’re indoors because the virus can build up in the air.”