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CDC backtracks on new guidance on how coronavirus spreads through air
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Lyman Hall Elementary students eat their lunch outdoors Monday, Sept. 14, 2020. Students wear masks when indoors and many eat their lunches outdoors to prevent spread of COVID-19. - photo by Scott Rogers

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Update, 9:45 p.m.:  The top U.S. public health agency stirred confusion by posting — and then taking down — an apparent change in its position on how easily the coronavirus can spread from person to person through the air, and this week, local health officials weighed in.

But officials at the Centers for Disease Control and Prevention say their position has not really changed and that the post last week on the agency's website was an error that has been taken down.

It was "an honest mistake" that happened when a draft update was posted before going through a full editing and approval process, said Dr. Jay Butler, the CDC's deputy director for infectious diseases.

The post suggested that the agency believes the virus can hang in the air and spread over an extended distance. But the agency continues to believe larger and heavier droplets that come from coughing or sneezing are the primary means of transmission, Butler said.

Most CDC guidance about social distancing is built around that idea, saying that about 6 feet is a safe buffer between people who are not wearing masks.

In interviews, CDC officials have acknowledged growing evidence that the virus can sometimes be transmitted on even smaller, aerosolized particles or droplets that spread over a wider area. Certain case clusters have been tied to events in which the virus appeared to have spread through the air in, for example, a choir practice. But such incidents did not appear to be common.

Dr. John Delzell, vice president for graduate medical education and COVID-19 incident commander for the Northeast Georgia Health System, said the health system had already "been working under the assumption that there was some aerosolization" but, "The real difference of what (the CDC) is talking about is whether you get this by somebody coughing or breathing in a way that makes the particles go through the air and then land on you or something that you touch, versus the particles are sort of floating around in the air and then as you breathe that air, you have a chance to absorb them in," Delzell said. "... Aerosolization is when they are actually just floating in the air."

Delzell said transmission of the virus is more likely the closer two people are to each other. 

"The risk goes down the farther away from someone that you are," Delzell said. "The risk probably isn't zero if you're six feet away from somebody."

Wearing a mask can both prevent someone from breathing in particles and from expelling them into the air, he said.

"Anything you do like a mask, or even the face shields we wear with the hospitalized patients, can decrease the risk," he said. 

Public health experts urge people to wear masks, which can stop or reduce contact with both larger droplets and aerosolized particles.

But for months, CDC officials said little about aerosolized particles. So when the CDC quietly posted an update Friday that discussed the particles in more detail, the agency's position appeared to have changed. The post said the virus can remain suspended in the air and drift more than 6 feet. It also emphasized the importance of indoor ventilation and seemed to describe the coronavirus as the kind of germ that can spread widely through the air.

The post caused widespread discussion in public health circles because of its implications. It could mean, for example, that hospitals might have to place infected people in rooms that are specially designed to prevent air from flowing to other parts of the hospital.

But the CDC is not advising any changes in how far people stay away from each other, how they are housed at hospitals or other measures, Butler said.

The CDC has come under attack for past revisions of guidance during the pandemic, some of which were driven by political pressure by the Trump administration.

Butler said there was no external political pressure behind the change in this instance. "This was an internal issue,. And we're working hard to address it and make sure it doesn't happen again," he said.

In a statement released Monday, the CDC said the revisions to the "How COVID-19 Spreads" page happened "without appropriate in-house technical review."

"We are reviewing our process and tightening criteria for review of all guidance and updates before they are posted to the CDC website," the statement said.

At least one expert said the episode could further chip away at public confidence in the CDC.

"The consistent inconsistency in this administration's guidance on COVID-19 has severely compromised the nation's trust in our public health agencies," said Dr. Howard Koh, a Harvard University public health professor who was a high-ranking official in the Department of Health and Human Services during the Obama administration.

"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 difficult fall and winter season," Koh said in a statement.

The Associated Press and Times reporter Megan Reed contributed to this report.


Previous story: 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.

The Associated Press contributed to this report.

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