Is Covid-19 airborne? The CDC can’t say yet

The CDC posted and then retracted a statement about Covid-19 being an “airborne” disease. While the 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 organisation 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 neighbours 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 socialise 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 UK 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.

—Bloomberg