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This One Thing Is Secretly Spreading COVID-19, Say Scientists

The recent surge in coronavirus cases in the South may be due to this indoor appliance.

Is the recent surge of coronavirus cases a result of the warmer weather in western and southern states? Not precisely, but it is linked in an unsuspecting way. Scientists have noted that people's reliance on air conditioners in warm summer months—and in particular, the recirculation of air in their homes and in public buildings, like restaurants and bars—can increase the concentration of air that others are exhaling.

In other words, while you might be enjoying a more comfortable temperature inside in the A/C, you are also inhaling the air that's been exhaled by others (which may contain germs, bacteria, or coronavirus) and then recirculated throughout the building.

"You're breathing a higher percentage of the same air that other people are exhaling," Edward Nardell, MD, professor of environmental health and immunology and infectious diseases at Harvard's T.H. Chan School of Public Health, explained to WebMD.

HVAC systems have built-in energy efficiency systems that adjust the amount of fresh air being pulled in from outdoors when the temperatures are high, and instead, recirculate more indoor air. So the warmer the temperatures? The more indoor air gets recirculated—which increases the chances of spreading COVID-19 if someone in the space has the virus.

Also, Dr. Nardell noted to WebMD that many air conditioner systems remove moisture, which makes air dryer and more welcome for viruses.

There is a growing body of evidence that indicates the riskiest place to contract the COVID-19 contagion is indoors, particularly areas that are poorly ventilated. Airborne droplets that are exhaled can hang in the air for an extended period of time. If someone within the same building is sick, bacteria and germs can spread more easily with less ventilation.

The airborne transmission of the virus has become a widely accepted concern in scientific communities, and the increased recirculated air in homes relying on air conditioning may very well be a significant variable in the current increase in cases. "Based on our assessments of outbreaks, air sampling, and animal studies and we have just as much evidence to show that airborne transmission is happening as is surface transmission, so we need clear guidance for how to address this," Shelly Miller, PhD, a professor of mechanical engineering who studies indoor air quality at the University of Colorado at Boulder, told WebMD.

For now, Miller suggests to keep your house cool as best you can by relying less on air conditioning and more on outdoor air—opening up windows and doors. She also suggests investing in an air cleaner, and researching the best one to buy at Association of Home Appliance Manufacturers. In public places like grocery stores, do the best you can to keep your shopping trip to under 15 minutes, which experts say is the time it takes to contract coronavirus in indoor places.

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