Two weeks after removing language that acknowledged COVID-19 spreading through aerosols, the Centers for Disease Control and Prevention officially added a new section to its website Monday declaring that “COVID-19 can sometimes be spread by airborne transmission.”
The update reads: “Some infections can be spread by exposure to virus in small droplets and particles that can linger in the air for minutes to hours. These viruses may be able to infect people who are further than 6 feet away from the person who is infected or after that person has left the space.”
The organization reaffirmed that the main route of transmission remains respiratory droplets, which are released through things like coughing and sneezing. These droplets, which are often larger in size, spread the virus through contact with a mucous membrane, such as the eyes or nose. Aerosols, which are smaller, can linger in the air for hours and can spread through inhalation alone.
Although more research is needed to determine exactly how prevalent airborne transmission is, the CDC now acknowledges that it can occur. “There is evidence that under certain conditions, people with COVID-19 seem to have infected others who were more than 6 feet away,” the CDC writes. “These transmissions occurred within enclosed spaces that had inadequate ventilation. Sometimes the infected person was breathing heavily, for example, while singing or exercising.”
Multiple outbreaks have been reported from choir practices, including one in Washington in early March that led to 53 COVID-19 infections and two deaths. The CDC elaborates on what may be happening at these events. “Under these circumstances, scientists believe that the amount of infectious smaller droplet and particles produced by the people with COVID-19 became concentrated enough to spread the virus to other people,” the CDC writes. “The people who were infected were in the same space during the same time or shortly after the person with COVID-19 had left.”
On Twitter, both epidemiologists and aerobiologists, who have at times disagreed on the issue, praised the CDC’s guidance. Dr. Kimberly Prather, director for the NSF Center for Aerosol Impacts on Chemistry of the Environment (CAICE) at the University of California, San Diego, tweeted that she was “feeling hopeful” in the wake of the CDC update, along with a newly published paper in Science urging the medical world to “harmonize discussions about modes of virus transmission”
Dr. Saskia Popescu, an infection prevention specialist at George Mason University, tweeted that the document is “important” and that it “sheds light on situational airborne (aerosol) spread, close contact as a driving factor, & prevention strategies.” She added that the new information “doesn’t change the recommendations” but “rather reinforces what we’ve been saying — mask, distance, avoid crowded indoor spaces, adequate ventilation, hand hygiene, and cleaning/disinfection.”
Dr. Amesh Adalja, an infectious disease expert and senior scholar at Johns Hopkins University Center for Health Security,