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The CDC says the coronavirus spreads mainly through respiratory aerosols

The coronavirus spreads most often in the air, through droplets or other small respiratory particles that can apparently remain suspended and inhaled, says the Centers for Disease Control and Prevention in a new guide.

Smaller particles, known as aerosols, are produced when an infected person coughs, sneezes, sings, talks or breathes and can inhale 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 infection.

“This is thought to be the main way the virus spreads,”

; the CDC said on its website. “There is growing evidence that droplets and particles in the air can remain suspended in the air and be inhaled by others and travel distances of more than six feet (for example, during choral practice, in restaurants or in fitness classes).”

Aerosol and coronavirus experts say the change represents a profound change in understanding of how the virus has spread, killing nearly 200,000 people in the United States. However, the updated two-page explanation provided some new guidelines on how to avoid airborne transmission.

Earlier, the Federal Health Agency had said that the coronavirus spread mainly between people about six feet apart and by directly driving exhaled droplets that land in people’s noses and mouths nearby. The CDC also said – and still says – that people can become infected by touching something that has a virus on it and then touching their mouth, nose or eyes, but this touch is not the main way it spreads.

Researchers studying the transmission of the deadly virus noticed the new guidelines on Sunday on the CDC website, marked as an update from Friday. As with some other updates, the CDC made major changes to its guidelines without issuing a notice.

The CDC did not respond to requests to discuss the update on Sunday.

The CDC website says the guidelines say that in addition to wearing masks, washing their hands and standing “at least six feet away” from others, people should stay home and isolate themselves when they are sick and “use air purifiers.” to help reduce indoor germs. space. “Previously, the advice was to maintain a ‘good social distance’ of ‘about six feet’.

The CDC and the World Health Organization have long opposed the idea that the coronavirus spreads more than about six feet in 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 remain indoors and potentially infect humans. even when practicing social distancing.

Aerosol scientists have found growing evidence – including “over-spreading” events such as choral practices that have infected many people – that the virus can spread through microscopic respiratory particles. This week, the scientific journal Indoor Air published an article that found that many of the 53 singers of people who fell ill after attending a practice on March 10 in Mount Vernon, Washington, probably caught COVID-19. by air transmission.

Jose-Luis Jimenez, an aerosol scientist at the University of Colorado Boulder and one of the authors of the report, said in an interview Sunday that the CDC’s updated guidelines represent a major change. So far, he said, scientists from the agency claim that the virus is transmitted through the air when droplets are fired from a person’s mouth or nose in the form of shells, directly infecting another person.

“They changed it and didn’t tell anyone,” he said.

Donald Milton, a professor of environmental health at the University of Maryland and an aerosol expert, said in an interview Sunday that the CDC has gradually come up with the concept of airborne transmission as evidence has accumulated and he notes that the agency has introduced sudden changed its guidelines in the past.

“They pay attention and move in response to research, so I’m glad to see that they continue and that no one is interfering,” he said.

Without notice in May, the CDC changed the guidelines for opening homes of prayer by deleting a warning issued the previous day that the act of singing could contribute to the transmission of the coronavirus, a change announced by White House pressure. Friday’s updated guidelines identify singing as one of the activities that can produce infectious aerosols.

Jimenez and Milton said it was important to wear masks to reduce the risk of spreading and negotiating COVID-19. They said it was crucial to make sure that the face sheets fit properly so that the aerosols did not come out or enter through gaps in the mask around the nose or mouth.

“Aerosols can travel farther than six feet, but they’re more concentrated the closer you get, so staying as far away as possible reduces the risk,” Milton said. “The reason bars have been such a big problem is that people get strong when they bring alcohol on board and come close to hear, and you can’t drink beer or a shot with a mask on it.”

Milton and Shelley Miller, another aerosol researcher at the University of Colorado Boulder, are exploring ways to make singing and playing wind instruments safer by distancing, ventilating, and masking with different types of materials. The study is funded by national choirs and instrumental associations, whose members failed to come together during the pandemic.

Good ventilation reduces the risk of indoors, as well as simply opening windows to allow air to circulate, the researchers said. Ceiling fixtures that use ultraviolet light to kill the virus also promise, they said.

Milton and Jimenez were among a group of researchers who drafted an open letter to the WHO, eventually signed by 239 researchers from 32 countries, urging officials to accept the possibility of aerosols playing an important role in the spread of the virus. The WHO revised its guidelines after receiving the letter on July 6, saying the air show had not been definitively demonstrated, but advised people to avoid poorly ventilated, crowded spaces.

Now the CDC has taken another important step to recognize the role of aerosols, Jimenez said.

“The whole field of aerosol science tells them that the understanding of ballistic droplets is outdated and indeed aerosols spread the virus,” he said.

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