Coronavirus can spread farther than thought indoors, CDC says
Two weeks after the Centers for Disease Control and Prevention took down a statement about airborne transmission of the coronavirus, the agency Monday replaced it with language citing new evidence that the virus can spread beyond 6 feet indoors.
“These transmissions occurred within enclosed spaces that had inadequate ventilation,” the new guidance said. “Sometimes the infected person was breathing heavily, for example while singing or exercising.”
The incident was only the latest in a series of slow and often puzzling scientific judgments by the CDC and by the World Health Organization since the start of the pandemic. Despite evidence that use of face coverings can help cut down on viral spread, for example, the CDC did not endorse their use by the public until April, and the WHO did not do so till June.
Regarding aerosols — tiny airborne particles — the
CDC lagged behind even the WHO. In July, 239 experts who study aerosols called on the WHO to acknowledge that the coronavirus can be transmitted by air in any indoor setting and not just after certain medical procedures, as the organization had claimed.
Notably, the CDC’s new guidance softens a previous statement referring to the coronavirus as “an airborne virus,” a term that may have required hospitals to treat infected patients in specialized rooms and healthcare workers to wear N95 masks anywhere in a hospital.
The new advice instead says the virus can “sometimes be spread by airborne transmission” and can be spread by both larger droplets and smaller aerosols released when people “cough, sneeze, sing, talk, or breathe.”
But while the virus can be airborne under some circumstances, it is not the primary way the virus spreads, the CDC said.
“I’m a little concerned that they still distinguish between close contact and airborne transmission, implying that airborne transmission only matters beyond 6 feet,” said Linsey Marr, an expert in airborne transmission of viruses at Virginia Tech. “Airborne transmission also occurs at close contact and is probably more important than the spray of large droplets.”
The revisions arrived as President Donald Trump received treatment at Walter Reed National Military Medical Center in Bethesda, Maryland, for what might be a severe case of COVID-19, the illness caused by the SARS-CoV-2 coronavirus. (Trump was discharged from the hospital Monday evening.)
The administration is contending with a rising number of such infections among Trump’s inner circle. Kayleigh McEnany, the president’s chief spokeswoman, announced Monday that she had tested positive for the coronavirus, the latest in a string of political figures heading into selfquarantine following what might have been a so-called superspreader event at the White House late last month.
That ceremony, a celebration of Judge Amy Coney Barrett’s nomination to the Supreme Court, involved close contact both indoors and outdoors by attendees who wore no masks.
The new language on the CDC website makes some of the same points as a previous version, which quietly appeared on the CDC website Sept. 18 and was taken down just three days later.
At the time, CDC officials said the document had been posted in error and had not yet been cleared through the agency’s rigorous scientific review.
In both documents, the agency emphasized the risk of infection in poorly ventilated indoor environments.
Under such circumstances, the amount of infectious smaller droplets and particles expelled by people with COVID-19 “became concentrated enough to spread the virus to other people,” the agency said, even to those who arrived in a room shortly after an infected person left.
But the new version struck a more conservative tone on airborne transmission, saying it is much more common for the virus to spread through close contact with an infected person than through airborne transmission. Some experts praised the softer emphasis on airborne transmission.
“This is consistent with what the epidemiological data has shown us — opportunistic and situational airborne events do occur, but close contact is really where it’s at,” said Saskia Popescu, a hospital epidemiologist at George Mason University in Fairfax, Virginia.
But Monday, a group of aerosol scientists, including Marr, contended the opposite in a letter to the journal Science. “There is overwhelming evidence that inhalation represents a major transmission route,” the researchers wrote.
The new guidance takes on urgent importance as cooling temperatures send people back indoors, where risk of the virus spreading by air is highest.
The agency’s advice also guides managers of schools, offices, hospitals and other public buildings in preparing for the winter by improving their ventilation systems and taking other precautions.