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Is the coronavirus airborne? It’s complicated.

How a quirk of scientific jargon is confusing and endangering us.

A single case of measles can cause 12-18 other cases, because measles is “airborne” — particles of the virus linger in spaces for hours after sick people breathe or cough them out. This characteristic is uncommon, and it makes the measles virus one of the most infectious known to humans. Because airborne diseases spread so quickly, civilians and scientists alike have been nervously wondering: Is the SARS-CoV-2 coronavirus airborne?

The answer, however, is complicated. First, not everyone agrees on what airborne means. The WHO and many infectious disease researchers use a highly specific definition for “airborne” that’s not intuitive to most people. This leads to situations such as this: The CDC has recommended Americans wear face masks in certain public settings to prevent catching or spreading the disease, even though the coronavirus might not meet the CDC’s definition of airborne.

Second, the evidence needed to declare the coronavirus officially “airborne” could take years to gather, while possibly endangering people. After a large choir in Washington rehearsed together, 45 of the 60 members got sick, even though nobody was symptomatic at the time.

On an episode of Reset, host Arielle Duhaime-Ross spoke to science writer Roxanne Khamsi about the origins of the “airborne” debate, and whether we should stop using the term altogether. Below, we’ve shared a lightly edited transcript of their conversation.

Arielle Duhaime-Ross

What exactly does airborne mean?

Roxanne Khamsi

So there is not a great answer to that question. I think that you can take a very simplistic view, which means airborne means something is in the air. I mean, if you open the dictionary, that’s what it means. … But a lot of virologists and especially a lot of public health officials have the idea that something is airborne if it is spread by aerosol and not by droplet. Now, you’re wondering, like, what is the difference between droplets and aerosols, right?

Arielle Duhaime-Ross

Yeah, that is 100 percent what I’m thinking right now.

Roxanne Khamsi

So traditionally, public health officials, at least recently, have been defining the droplet as something that’s like a ball of mucus and virus and salts that is larger than five microns in diameter that you’re kind of coughing up or spewing out. And anything smaller than that could be an aerosol that floats around … in the air because it’s lighter. Imagine like a feather or like floating in the air.

Arielle Duhaime-Ross

Okay, so there are large droplets that can float around in the air, and there are fine aerosols that last longer in the air. That’s the distinction?

Roxanne Khamsi

Right. And if you trace back where they came up with this, it goes back to these equations from the 1930s where people were trying to figure out tuberculosis and how it spread. So we’re talking about a really antiquated point of view on these things. I asked the WHO, how do you know that this [coronavirus] isn’t airborne? How do you know it’s only in droplets? And I did not get a good answer from them.

Arielle Duhaime-Ross

So why are some scientists still saying that we don’t know if the virus that causes Covid-19 is airborne?

Roxanne Khamsi

Because we don’t. The thing is, we actually don’t have evidence to say whether it’s airborne or not. In a normal setting, I mean, in settings where people are getting intubated and that’s kind of spewing this thing into the air, even the WHO says there is a risk of it being airborne in those situations, but we’re operating in an absence of evidence.

Arielle Duhaime-Ross

What I’m getting from you is that … you can’t tell me right now whether it is or it’s not. We just don’t know.

Roxanne Khamsi

Exactly. So the people I spoke with who witnessed SARS almost 20 years ago and dealt with that public health disaster, they’re saying that we should operate on the precautionary principle, that this is more easily airborne than we’re saying it is or assuming it is because it technically does travel in the air. So it is, quote unquote, airborne.

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