CDC updates guidance stating COVID-19 can be airborne

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The U.S. Centers for Disease Control and Prevention (CDC) updated its public guidance Friday on how the novel coronavirus (COVID-19) spreads, now explicitly stating airborne transmission is possible. The virus can be inhaled even when one is more than six feet away from an infected individual, the guidance states.

The new language changes the agency’s previous guidance, which said most infections were acquired through close contact and not airborne transmission.

According to the CDC, principal mode by which people are infected with SARS-CoV-2, the virus that causes COVID-19, is through exposure to respiratory fluids carrying infectious virus. Exposure occurs in three ways, the inhalation of very fine respiratory droplets and aerosol particles, the deposition of respiratory droplets and particles on exposed mucous membranes in the mouth, nose, or eye by direct splashes and sprays, and touching mucous membranes with hands that have been soiled either directly by virus-containing respiratory fluids or indirectly by touching surfaces with virus on them.

People release respiratory fluids during exhalation in the form of droplets in a variety of sizes. These droplets carry virus and transmit infection. The largest droplets settle out of the air rapidly, within seconds to minutes. The smallest very fine droplets, and aerosol particles formed when these fine droplets rapidly dry, are small enough that they can remain suspended in the air for minutes to hours.

Once infectious droplets and particles are exhaled, they move outward from the source. The risk for infection decreases with increasing distance from the source and increasing time after exhalation, the agency said.

Infections through inhalation at distances greater than six feet from an infectious source are less likely than at closer distances, however the phenomenon has been repeatedly documented under certain preventable circumstances. Such cases occurred in enclosed spaces with inadequate ventilation or air handling within which the concentration of exhaled respiratory fluids, especially very fine droplets and aerosol particles, can build-up in the air space, with increased exhalation of respiratory fluids if the infectious person is engaged in physical exertion or raises their voice, or with prolonged exposure to these conditions, typically more than 15 minutes.

The infectious dose of SARS-CoV-2 needed to transmit infection has not been established, the CDC said.

“Although how we understand transmission occurs has shifted, the ways to prevent infection with this virus have not,” said the CDC statement. “All prevention measures that CDC recommends remain effective for these forms of transmission.”

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