Woman with face mask coronavirus
Woman with face mask coronavirusiStock

A recent study suggests air conditioning systems could play a role in spreading the coronavirus.

The study looks at a woman in China who dined at a restaurant days before she showed COVID-19 symptoms. Researchers say she infected four people at her table and five at other tables because an air conditioner behind her spread droplets from her speech.

These findings suggest air conditioners can blow around infected droplets hanging in the air, says University of Maryland environmental health professor Donald Milton. With enough air movement, your nose can pull in large particles, he says. Think pollen, for example.

The restaurant had exhaust fans that were sealed up at the time of the infections, he says.

“There was no fresh air coming in,” he says. “Outbreaks — where you have a bunch of people infected all at once like that — are almost exclusively occurring indoors in poorly ventilated environments.”

Some increasingly popular systems recirculate the air but don't bring in fresh air or provide filtration. Called splits, these air conditioners are popular because of their energy efficiency, he says.

Ceiling fans also move the air around but don’t limit the spread of the coronavirus, he says.

Building managers and property owners need to look into how air is circulating through their space. Through air dilution or ventilation coming from outdoors, researchers find each person in a room should have 5 to 10 liters of fresh or filtered air per second, he says.

During the 1918 flu pandemic, patients stayed in fresh air hospitals — tents with no walls. Doctors at the time deemed fresh air a disinfectant.

While fresh air doesn’t kill the virus, Milton says it dilutes the virus and reduces the level of exposure for humans, making infection less likely.

New data shows sunlight does work as a disinfectant, he says, though sunlight can’t kill the virus if someone is already infected.

“If you are with other people outdoors, you have infinite amounts of dilution, ventilation,” he says. “And if it's daytime and the sun is out, the sunlight is killing the virus that's in the air or on surfaces so that you have multiple modes of preventing transmission.”

But that doesn’t mean people should break social distancing rules outdoors, he warns. Maintaining a six-foot distance helps with all modes of transmission, he says: touching contaminated areas, breathing in contaminated micro-droplets and getting hit by big droplets.