CDC has finally acknowledged yesterday that we can become infected with COVID-19 through airborne transmission especially in rooms or spaces with inadequate ventilation. People farther than 6 feet apart can still be infected by tiny droplets and particles that float in the air for minutes and even hours. The CDC says that despite this information, the main way the virus spreads through close contact with both large and small virus-containing droplets produced when someone sings, talks, breathes, sneezes, coughs or exercises

These particles can remain suspended over long distances and time meaning one can get infected if they arrive at a room where someone who had COVID-19 was hours before. The likelihood, however, increases with the longer and closer we are to an infected person.

When there is adequate ventilation, respiratory droplets are diluted by outdoor air or pushed out by air exchanges, according to experts. To improve indoor airflow in public buildings, experts at the Yale School of Public Health recommend switching off sensor-based ventilation to more constantly flush air. Open windows for fresh breezes, they said. And reverse ceiling fan blades, which can draw air up, away from a room’s occupants.

Experts have pointed to the spread of the virus in choirs, buses, fitness classes and other poorly ventilated spaces. In July, more than 200 aerosol biologists and other experts sent a letter expressing concerns about airborne transmission to the World Health Organization, which responded by acknowledging the “emerging evidence” the pathogen can spread through the air.

A group of infectious-disease physicians and aerosol experts, in a letter published Monday in the journal Science, more strongly emphasized the airborne potential of the virus than the CDC did in its update.

“The balance of attention must be shifted to protecting against airborne transmission,” they said, because people are “far more likely” to breathe in floating virus than be sprayed by quickly falling droplets of contaminated body fluid.

Aerosols and airborne transmission “are the only way to explain super-spreader events we are seeing,” letter author Kimberly Prather, an atmospheric chemist at the University of California at San Diego, said in an interview. Once the airborne route is acknowledged, she said, this becomes a “fixable” problem through proper ventilation.

“Wear masks at all times indoors when others are present,” Prather said. Separation is important — but, inside, no such thing as a completely “safe social distance” exists.

Experts welcomed the CDC’s new guidance on airborne transmission

“There is overwhelming evidence that this is an important route of transmission for covid-19, and we have desperately needed federal guidance on this route,” said Linsey Marr, who studies aerosols at Virginia Tech and was an author of the Science letter. “I would like to emphasize that short-range airborne transmission when people are in close contact, meaning inhalation of aerosols, probably is more important than transmission by large droplets that are sprayed onto mucous membranes.”

Some of the debate about airborne transmission may stem not from substance but from terms used differently in the fields of aerosol chemistry and infectious disease. The Science letter clarifies that fluid blobs up to 100 microns wide (the thickness of a sheet of paper) can behave as aerosols, unlike some definitions focused on smaller particles.

“Aerosol biologists speak a slightly different language than, say, clinicians like myself do, where we’re looking more at the pragmatic application of transmission for infection control, especially in a health-care environment,” Jay Butler, the CDC’s deputy director for infectious diseases, said last month. He summed up a National Academies of Sciences workshop, convened in late August to discuss the growing evidence of airborne transmission, as having “much more agreement than disagreement” about its possibility

Covid-19 is not as contagious as measles or tuberculosis, which are primarily spread through airborne transmission and require hospitals and health-care settings to care for patients in special negative-pressure infection isolation rooms to prevent spread.

There have been several well-documented cases in which the coronavirus spread rapidly and widely in an enclosed or indoor environment — a restaurant in Guangzhou, China; a bus traveling in China’s Zhejiang province; a call center in Seoul; and a church choir in Washington state. In that instance, a singer spread the virus up to 45 feet away and infected more than 50 people.

Those reports prompted the CDC to update its guidance about coronavirus transmission, officials have said. Adding to that urgency is the arrival of fall and colder weather when people will be indoors.

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