CDC says coronavirus can spread through tiny airborne particles

The U.S. Centers for Disease Control and Prevention acknowledged Monday that the coronavirus can spread through microscopic respiratory particles known as aerosols that float in the air for minutes or even hours before being inhaled.

On its website, the CDC said that even people who followed social distancing guidelines have been infected through this type of transmission – and added a warning against frequenting crowded, poorly ventilated indoor spaces.

The acknowledgement comes after months of campaigning by independent experts and brings the agency into line with research on the role of aerosols in “superspreading events” such as a choir practice in Washington state that infected dozens of people and killed two.

But some researchers said the agency did not go far enough, because it maintains that the virus is still far more likely to spread through larger respiratory droplets that quickly fall on people in close vicinity.

Donald K. Milton, a University of Maryland environmental health professor and expert on aerosols, said Monday that the CDC was “slowly moving along in the right direction, but is not where I would quite like to see it.”

He said that mathematical models show that aerosols carrying the virus are more apt to spread the disease than larger droplets spewed as projectiles, even when an infected person is less than 6 feet away.

“At close range, you’re still going to see aerosol transmission dominant most of the time,” he said. “Spitballs are much less frequent.”

He said that means that masks – which the CDC has long recommended be worn when near others – are useful both indoors and outdoors for preventing the spread of the virus.

“Outdoor dining is associated with increased risk of getting COVID-19 because people are sitting there for a long time without a mask in one spot,” he said.

Moving around when outdoors lowers the risk of inhaling aerosols and becoming infected, he said.