The World Health Organization (WHO) has acknowledged that the deadly COVID-19 can spread through the airborne particles breathed out by infected persons in closed and indoor spaces. Following the declaration, Harvard epidemiologist Dr. Edward Nardell has come up with his study suggesting that the air conditioners might also be contributing to the airborne transmission of the virus.

“Outside of medical facilities, some outbreak reports related to indoor crowded spaces have suggested the possibility of aerosol transmission, combined with droplet transmission, for example, during choir practice, in restaurants or in fitness classes,” the WHO said in its latest guidance.

According to Dr. Nardell, ACs increase the risk of transmission through airborne particles, especially those installed in closed public spaces with a large number of people present.

The ACs block fresh air from the outside to cool down the closed spaces and people present in the space are forced to breathe the same air particles exhaled by someone else.

“We call it rebreathed air fraction, and if someone is infectious, often asymptomatic, you’re going to be rebreathing their small particles,” Dr. Nardell was quoted as saying by ABC Action News.

The Harvard scientist added that infected particles coming out of the air conditioning unit can be removed with the help of UV light-based germicidal lamps.