Monday's reversal may also increase public skepticism about the agency's messaging on COVID-19 more broadly.
The agency says the guidance was a draft version of proposed changes that was posted in error to its website. "CDC now says SARS-CoV-2 virus is being spread in aerosols", tweeted Kimberly Prather, a professor at UC San Diego's Scripps Institution of Oceanography and in the university's department of chemistry and biochemistry.
In the original change, the CDC cited "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".
Because on Friday they had posted that "It is possible that COVID-19 may spread through the droplets and airborne particles that are formed when a person who has COVID-19 coughs, sneezes, sings, talks, or breathes".
CDC Says Recommendations About Airborne Transmission of Coronavirus Were 'Posted in Error'
Friday's "clarification" returns the CDC's stance on testing to its previous guidance, before the August adjustment . "Airborne viruses, including Covid-19, are among the most contagious and easily spread", the site now says.
"The latest report shows that indoor dining, bars, restaurants are the leading leading factors for transmission, once you do contact tracing", he said, noting that this leads naturally to the big issues around schools reopening, including that many have "very poor ventilation", while simultaneously they're not able to open their windows or doors due to gun safety protocols in place.
In a section of the agency's website titled "How COVID Spreads", the CDC acknowledged for the first time that "droplets and airborne particles" can stay in the air and infect others - a mode of spread that has been supported by widespread evidence for months, and which President Trump acknowledged in a February phone call with Bob Woodward.
"To rectify the latest challenge, the CDC must acknowledge that growing scientific evidence indicates the importance of airborne transmission through aerosols, making mask wearing even more critical as we head into the hard fall and winter season".
The agency still believes the disease is primarily spread through droplets, but that in enclosed crowded spaces with inadequate ventilation, aerosol transmission can occur, said Mike Ryan, executive director of the WHO's emergencies program. Until now, he said, agency scientists have said that the virus is transmitted through the air when droplets shoot out of one person's mouth or nose in the form of projectiles, directly infecting another person.
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The posting appeared to confirm emerging research that suggests tiny particles can transport the virus some distance, especially in indoor or poorly ventilated environments.
Experts are anxious the CDC guidance, which applied to both asymptomatic close contacts as well as those who attended large, risky gatherings but had no symptoms, would exacerbate those challenges. The guidance also stated that these particles might travel farther than 6 feet.
Previously, the CDC warned larger "respiratory droplets" created from coughing or sneezing were the primary transmitter for coronavirus. That change had set off a rash of criticism from health experts who couldn't fathom why the nation's top public health agency would say such a thing amid the pandemic.
Cover your mouth and nose with a mask when around others.
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Despite these new developments, nothing has changed about the virus itself and the precautions each individual needs to take to minimize the spread.