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BMC Medical staff conducting a rapid antigen test at Mahim in Mumbai. (ANI)
BMC Medical staff conducting a rapid antigen test at Mahim in Mumbai. (ANI)

Is covid-19 airborne? Experts can't say yet

What scientists are learning is that airborne particles carrying the virus are dispersed outside, where the risk is low

On Monday, the CDC posted and then retracted a statement about Covid-19 being an “airborne" disease. While switch generated tons of attention from the press, infectious disease experts say it’s not clear it would have made much difference if the word had remained. The term might just confuse the public even more.

The more serious problem is that we are losing faith in the CDC just when we need it the most. Until recently, the organization was a model for similar ones around the world and was admired as a trusted source of information.

“The CDC needs to work out what their messaging is because lately it’s been terrible," says University of Massachusetts biology professor Erin Bromage, who has been offering advice on risk reduction throughout the pandemic.

Airborne transmission means different things to different people. If thrown at the public with no explanation, it might suggest, wrongly, that conversations with neighbors across the street are high risk. They aren’t. What scientists are learning is that airborne particles carrying the virus are dispersed outside, where the risk is low. Infectious disease experts have told me they do socialize outdoors or with windows open.

But virus particles can build up indoors. That means that in poorly ventilated spaces, people may become infected even if they remain more than six feet apart. That’s the important part of the message — that people might get infected in crowded, poorly ventilated indoor spaces.

Nonetheless, the term “airborne" could easily generate fears that would further confuse the public.

“I think we really need to take away all the terminology and translate that to practical terms because I think the confusion comes from different fields having a different view of what aerosol means and what needs to be done," says Muge Cevik, an infectious disease specialist at the University of St. Andrews in the U.K. The term “aerosol" is often used interchangeably with airborne, though there are distinctions, none of which matter for any practical recommendations from the CDC.

In a healthcare setting, said Cevik, “airborne" means patients need to be in a negative pressure unit and healthcare workers need to wear full protective gear and N95 masks. That’s the case for measles, tuberculosis and chicken pox. Most hospitals took those precautions early on with SARS-CoV-2, she says. But they’ve since found that wearing ordinary surgical masks outside of the ICU works to avoid acquiring the virus from patients.

In hospitals, Cevik says, most infections are coming from close contact with patients, or being in the same room with an infected patient for a prolonged period of time. That’s shown up in contact tracing studies looking at how the disease is spreading in the wider community too. Length of exposure matters as well as proximity.

She worries that the concept of airborne transmission has become politicized, the same way asymptomatic transmission has, along with the role of children and schools.

One of the correct implications of airborne transmission is that many people who got the disease were not careless or immoral, but simply stuck in poorly ventilated environments — prisons, homeless shelters, apartment buildings or conference spaces. Some are stuck in bad working conditions, such as meat-packing facilities.

Bromage, the biology professor at UMass, says a good analogy is to think of the virus a bit like cigarette smoke. If someone is smoking indoors, it doesn’t take long for everyone to start to breathe it in. Outdoors, only those nearby are likely to be adversely affected.

Air filtration matters too. He’s argued that because airplane cabins are better ventilated than most indoor spaces, flying is surprisingly low risk. There have been a few documented airplane transmissions, mostly from before airlines required masks and were still allowing coughing people onboard. But the number of transmissions is tiny compared to the total number of airline passengers.

What the CDC appears to be retracting, he says, is the notion that airborne transmission is the primary route of disease spread. While there’s agreement that it happens and that it matters, it’s not established whether this is the primary route, or whether the so-called droplet route is more important, by which people infect others at close range.

But the appearance of inconsistency is bad, he says. “It took a long time to get to the recognition that airborne is a part of this, and then to immediately change and pull that away just sows huge doubts about what people should believe from CDC," he says. “Something is breaking down in the public dissemination process that does not seem appropriate for an organization that is as good as they are."

Bromage says the problems at the CDC have more to do with its public face than its internal workings. The agency is still full of great scientists, he says. It even still has some of the same people who, after the 2001 anthrax attacks, devised what he considers an excellent public messaging playbook. But they’re not following this playbook now.

In fact, it’s not clear if they’re following any playbook at all.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Faye Flam is a Bloomberg Opinion columnist. She has written for the Economist, the New York Times, the Washington Post, Psychology Today, Science and other publications. She has a degree in geophysics from the California Institute of Technology.


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