The coronavirus spreads most commonly in the air, through droplets or other tiny respiratory particles that apparently can remain suspended and inhaled, the Centers for Disease Control and Prevention says in new guidance.
The smaller particles, known as aerosols, are produced when an infected person coughs, sneezes, sings, talks or breathes and can be inhaled into someone's nose, mouth, airways or lungs, according to the CDC, which says that, in general, indoor settings without good ventilation increase the risk of contagion.
"This is thought to be the main way the virus spreads," the CDC has posted on its website. "There is growing evidence that droplets and airborne particles can remain suspended in the air and be breathed in by others and travel distances beyond 6 feet (for example, during choir practice, in restaurants or in fitness classes)."
Experts on aerosols and the coronavirus said the change constitutes a profound shift in understanding of how the virus that has claimed almost 200,000 lives in the United States spreads. However, the updated two-page explanation provided little new guidance on how to protect against airborne transmission.
Previously, the federal health agency had said the coronavirus spreads mainly between people within about 6 feet of one another and through direct propulsion of exhaled droplets that land in the noses and mouths of individuals nearby. The CDC also said - and still says - that people may become infected by touching something that has the virus on it and then touching their mouth, nose or eyes, but that touch is not the main way it spreads.
Researchers studying transmission of the deadly virus noticed the new guidance Sunday on the CDC's website, labeled as an update from Friday. As with some other updates, the CDC made the fundamental changes to its guidance without issuing an announcement.
The CDC did not respond Sunday to requests to discuss the update.
In the guidance, the CDC website says that in addition to wearing masks, washing hands and staying "at least 6 feet away" from others, people should stay home and isolate themselves when sick and "use air purifiers to help reduce airborne germs in indoor spaces." Previously, the advice was to maintain "good social distance" of "about 6 feet."
The CDC and the World Health Organization have long resisted the notion that the coronavirus spreads farther than about 6 feet through the air, with the WHO initially maintaining that airborne transmission occurred only during certain medical procedures. But in July, under growing pressure from researchers, the WHO acknowledged that the virus could linger in the air indoors and potentially infect people even when they practice social distancing.
Aerosol scientists have found mounting evidence - including "super-spreading" events such as choir practices in which multiple people were infected - that the virus can spread through microscopic respiratory particles. This week, the scientific journal Indoor Air accepted a paper for publication that found that many of the 53 choir singers who became sick after attending a March 10 practice in Mount Vernon, Washington, likely caught COVID-19 through airborne transmission.