Coronavirus FAQs: Why can't the CDC make up its mind about airborne transmission?

Each week we answer some of your pressing questions about the coronavirus and how to stay safe. Email us your questions at goatsandsoda@npr.org with the subject line: "Weekly Coronavirus Questions."

What is up CDC? First you say airborne transmission is a thing. Then you rolled it back. So, is this something I should be worried about?

Last Friday, the U.S. Centers for Disease Control and Prevention briefly became the first major public health agency in the world to say the coronavirus could be frequently spreading through the air. A page on the CDC website on "How COVID-19 Spreads" described the coronavirus as spreading "most commonly" through "respiratory or small particles, such as those in aerosols," which are tiny airborne particles expelled from people's noses and mouths when they speak, sing, cough or breathe — and which can remain suspended in the air and travel further than 6 feet.

Aerosol researchers such as Linsey Marr, an engineering professor at Virginia Tech, who have been pushing for health agencies to officially recognize the potential importance of aerosol spread — cheered over the weekend.

But then, on Monday, CDC walked it back. "A draft version of proposed changes to these recommendations was posted in error," notes a box at the top of the CDC's page, adding that the agency is still working out what to say about aerosol transmission.

In the midst of this confusion, you might be wondering what exactly is in dispute. Does the coronavirus spread through the air? What precautions can help protect you?

The bottom line is: Yes, the coronavirus may be spreading through the air, particularly in stuffy rooms where many people aren't wearing masks.

Public health agencies such as CDC and the World Health Organization agree on that — it's why they've recommended that people avoid "confined and enclosed spaces with poor ventilation" and gather outdoors when possible.

They're just not clear whether it's one of the most common ways it spreads. CDC now maintains that the highest risk of catching the virus comes from spending prolonged time within 6 feet of an infectious person, and that it can also spread through touching a surface that someone infectious has sneezed or coughed on, and then rubbing your eyes, nose or mouth.

Some of the reluctance to describe COVID-19 as an airborne disease may stem from concerns that the label would scare the public and may require hospitals to take "a whole new level of precautions," says Marr, such as requiring an N95 mask, which blocks aerosols, to be worn around all potential COVID-19 patients.

Currently, WHO guidance considers surgical masks to be adequately protective for healthcare staffers working with potential COVID-19 patients, and advises using N95 masks in limited situations, such as when intubating patients, which is known to generate small particles from deep in the lungs. Healthcare workers who follow these recommendations have been generally protected against the virus, WHO notes.

Months of evidence point to the probability that COVID-19 is less contagious than measles, a designated airborne disease, but is still spreading through the air, says Jose-Luis Jiminez, an atmospheric chemistry professor at University of Colorado Boulder. He points to a March choir practice in Washington state, where 53 out of 61 attendees came down with COVID-19 after spending two and a half hours together at a singing rehearsal. "People who were 50 feet from the [person who was contagious] got infected," he says, based on investigations he and several colleagues conducted into the event.

Infection clusters have also emerged among students returning to college dorms, partiers in a nightclub district, guests at a wedding reception, residents in a nursing home, worshippers at a churches, staff and inmates at a prison. Most superspreading events, where many people catch the coronavirus at once, are occuring in indoor settings where people are sharing airspace.

So what precautions can you take to protect yourself against aerosol spread?

It means keeping that physical distance of 6 feet — and then thinking beyond it. "Masks and ventilation and filtration," says Marr, can go a long way in "getting a better control on the spread of the virus."

First, that recommended 6 feet of distance between you and others allows more air to pass between you, helping to dispel any clouds of virus that get released. It reduces the risk that one of you will breathe in an infectious dose.

Second, wear a face mask that covers your nose and mouth. It blocks the spray of spit and breath you expel, and also affords some protection from other people's exhalations. Unlike N95 masks, which form a seal on your face, a typical cloth or surgical mask isn't foolproof against aerosols — but Jimniez says that they offer reasonable protection, particularly when combined with other precautions.

"If you are outdoors with distance and with a mask that is well-fit, I would say it's extremely difficult to get the disease that way," Jiminez says.

If you do spend time indoors with others, work to improve the airflow and ventilation in the room. "We need to address ventilation in all of our public buildings, especially places like schools and restaurants," says Marr. "This can be as simple as opening doors and windows, it can be adjusting dampers and the HVAC system so that you bring in more outdoor air."

Air filters, which can be used to purify the air in a room, may help as well, she says. "There are simple things we can do to greatly improve ventilation in buildings that are not necessarily costly."

In most settings, these potential virus clouds can be dispersed with a light breeze and some fresh, clean air.

For more information about aerosols, read an FAQ explainer assembled by Marr, Jiminez and colleagues.

Copyright 2020 NPR. To see more, visit https://www.npr.org.

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