[RADIOLAB INTRO]

JAD ABUMRAD: Sarah Qari?

SARAH QARI: Hello. Whoa! Hi!

JAD: [laughs]

SARAH: You're coming through so clear. This is crazy!

JAD: It's pretty cool, isn't it?

SARAH: Yeah.

JAD: Hey, I'm Jad Abumrad. This is Radiolab. Coronavirus dispatch number four. This one is sort of a follow-up to our first dispatch. And it comes from producer Sarah Qari.

SARAH: In the last, I want to say, like, 48 hours, I feel like I've become a—an armchair expert on [laughs] on how pathogens travel out of your mouth.

JAD: Just—just to set it up. So, like, a couple days ago, I mean, it feels like 50 years ago, the whole group got together on Zoom and we started talking about numbers.

MOLLY WEBSTER: At some level, like, I'm sort of obsessed with all the numbers that are, like, coming out every day.

PAT WALTERS: 22 people here and 500 people there and ...

JAD: And I believe you had a question about numbers. A specific number.

SARAH: Sure, okay. A number that I've been thinking a lot about is six.

[NEWS CLIP: The recommended distance is six feet apart.]

[NEWS CLIP: And you could be infected and spreading it to anyone in your six-foot bubble.]

JAD: You mean, like, the distance we're supposed to stand apart from one another?

SARAH: Exactly.

[NEWS CLIP: Six feet between all people is not a suggestion.]

JAD: Yeah, it's funny now that you mention it. I feel like we're all developing this new physical instinct for—for that distance. Like, the other day I was at the—the grocery store and I felt—and I could see other people feeling like we all had these six-foot force fields around us, and we were altering the arc of our walks so that we would go around each other's force fields.

SARAH: Yeah, totally! Totally. And it made me wonder where did this number come from? And is six actually even the right number?

JAD: Okay.

JULIE FISCHER: You know, researchers are really interested in this question.

SARAH: So I called a bunch of experts that study this.

JULIE FISCHER: How far do infectious agents like bacteria and viruses spread?

SARAH: One of them was Dr. Julie Fischer.

JULIE FISCHER: Associate Professor of Microbiology and Immunology at Georgetown University.

SARAH: And when I talked to her ...

JULIE FISCHER: In the past, one of the big questions was ...

SARAH: ... I came across this history.

JULIE FISCHER: [laughs] It's a—a very strange area of research.

SARAH: The interesting thing about it too is that it's very much still evolving.

JULIE FISCHER: Well, some of the older studies ...

SARAH: Maybe the place to start is actually the 1930s. In the 1930s, there was this guy named William Wells, who was studying different diseases. And he made this discovery that, like, when you open your mouth, for example, like when you're breathing or you're coughing, right? Like, every time you do that, there's little particles that fly out of your mouth. And eventually we learned that those particles are flying pretty much all the time.

JAD: Just when you breathe, not even when you sneeze?

SARAH: Yeah. Yeah.

JULIE FISCHER: Everything I'm gonna say just sounds gross. People—people sometimes expel small amounts of moisture when they're talking, particularly if they're talking to someone very close up.

JAD: Wow, it's like little mouth rain.

SARAH: Yeah, exactly. Mouth rain. [laughs]

[NEWS CLIP: Droplets.]

[NEWS CLIP: Tiny droplets.]

[NEWS CLIP: Droplets.]

[NEWS CLIP: Invisible droplets.]

[NEWS CLIP: Bigger droplets.]

SARAH: Regardless of what you're doing, when you open your mouth and let out air, this is what's happening.

JAD: Okay.

SARAH: What happens next is, like, over the next few decades, like, scientists get really interested in how this works. And one of the first things they get really curious about is the common cold.

JULIE FISCHER: A lot of the research was done in England.

[ARCHIVE CLIP: At the Common Cold Research Unit at Harvard Hospital, Salisbury, there's literally a stream of people volunteering to catch cold.]

SARAH: Right after World War II in Salisbury in the UK, these scientists got together, a bunch of volunteers.

[ARCHIVE CLIP: Human guinea pigs have been living there in pairs for 10 days at a time.]

JULIE FISCHER: The place is often nicknamed the Honeymoon Clinic.

SARAH: [laughs] Okay.

JULIE FISCHER: Because they frequently recruited couples.

SARAH: Literally, they would offer people a 10-day, all-expenses-paid vacation in the Salisbury countryside.

[ARCHIVE CLIP: The food is good and the life quite comfortable, they say. The only thing is they're almost bound to have a cold, whereas ...]

JULIE FISCHER: In many instances, volunteers were deliberately infected with influenza.

SARAH: Researchers would take a little bit of cold virus, put it in an eyedropper ...

[ARCHIVE CLIP: This is how they're given colds, with drops in the nose.]

SARAH: ... shoot some virus up the honeymooners' noses, and then they'd watch to see what happened.

JULIE FISCHER: How easily did the people around them become infected? Did it require close contact? Could they just be in the same space?

JAD: I don't know if that sounds like a honeymoon anymore.

SARAH: Totally, it sounds like a raw deal but you'd be surprised. Like, people at the time, like, found this so appealing. People, essentially, just saw it as, like, an ideal budget holiday.

JAD: [laughs]

SARAH: Anyhow, jumping ahead, a few years, in later experiments, not at this clinic but in later experiments, they would have—you know, like, do things like oh, have infected and non-infected people sit together and play a game of cards for a bunch of hours. And then see how the disease has traveled from person to person.

JAD: Oh, they'd have like sick people and healthy people play together and see who got sick?

SARAH: Exactly. Also, they were quite interested in, like, when people sneezing and coughing, and like expelling again, these droplets into the air, like, how far are those traveling? And so one of the things that came out of these studies is that for the common cold, they found the droplets, the droplets are going about three feet.

JULIE FISCHER: That's where we came up with the three feet.

JAD: And this is three feet not through contact. This is just the mouth rain?

SARAH: Right. So simply being within three feet of someone puts you within the blast radius of their mouth rain.

JAD: Got it.

SARAH: For many, many years that was the sort of reigning understanding that, like, if you're gonna have a bubble around you it should have a three-foot radius. But then scientists realize that three feet might not be enough. And the way that they realize this is that in the early 2000s, when there are outbreaks of different kinds ...

JAD: 2000s! So this is recent!

SARAH: Yeah. Yeah, it's pretty recent. So ...

[NEWS CLIP: This week saw the galloping rise of SARS.]

SARAH: When there are outbreaks of different kinds like SARS ...

[NEWS CLIP: And tonight as health experts prepare for a possible H1N1 flu outbreak.]

SARAH: H1N1 or swine flu.

JAD: Hmm.

SARAH: Scientists and epidemiologists start to look at the patterns of how the disease is spreading. And actually, one type of information that was really useful to these scientists ...

ALBERT KO: This source of information actually comes from, a lot of times, with the airlines.

SARAH: So this is Dr. Albert Ko.

ALBERT KO: I'm at the Yale School of Public Health.

SARAH: He's the chair of the Epidemiology Department there.

ALBERT KO: So these are kind of these natural experiments where somebody has a respiratory illness, and they know how many seats in front and how many seats in back as well as in the side that people got sick.

SARAH: Let's say you're an epidemiologist tracking SARS, and you discover that the person sitting in seat 29A has the illness. So you then track everybody else on the plane to see what happens, and later find out that the person in 27A ended up getting sick too. So then you measure the distance between seat 29A and seat 27A. and it turns out to be more than three feet.

ALBERT KO: And they found that the people who had most risk were, you know, within two rows before and two rows behind, which is about six feet.

JAD: I see. So this is where it comes from?

SARAH: Yeah. And so then the CDC looks at that and they update their guidance based on that.

JULIE FISCHER: Again, the—the assumption is that six feet is about the distance that a droplet can travel.

SARAH: And so now with the virus that causes COVID-19, SARS COV-2 ...

ALBERT KO: Assuming that SARS COV is transmitted by droplets ...

SARAH: ... you can use that same rule.

JAD: You know, it's interesting. As you were talking I kept thinking about that idea of six feet under. How—how we bury people six feet under the ground, which apparently we only started doing in the 1660s because of the plague, to stop infections. So it's interesting, it feels like kind of this throughline number that's always—that's somehow always been there when we talk about trying to prevent spread.

SARAH: Right. But, that number is evolving.

[LISTENER: Hi, this is Zachary Ellis calling from Western Massachusetts where I'm celebrating my birthday in quarantine. Radiolab is supported in part by the Alfred P. Sloan Foundation, enhancing public understanding of science and technology in the modern world. More information about Sloan at www.sloan.org.]

JAD: This is Radiolab. I'm Jad Abumrad, here with Sarah Qari. We've been talking about the six foot rule when it comes to COVID-19 and how just over the past week or so that rule ...

[NEWS CLIP: So this is—we've been telling people six feet.]

JAD: ... might be evolving.

[NEWS CLIP: But now they're saying six feet may not be enough?]

[NEWS CLIP: That six feet may not be enough to prevent the spread of COVID-19.]

[NEWS CLIP: Health officials point to a Washington State choir practice where no one shook hands. 45 people were infected and two singers died.]

LINSEY MARR: In order to have what people call this large droplet spray transmission, you need to be facing the person. And the way I've seen choirs sing is they're all facing the same direction.

SARAH: This is Linsey Marr.

LINSEY MARR: Professor of civil and environmental engineering at Virginia Tech.

SARAH: She studies how diseases spread. And she says that that choir anecdote, where you had people just singing together and then a bunch of them getting sick ...

LINSEY MARR: I've gone through all the different scenarios in my head, and really the simplest explanation is that it was being spread through the air.

SARAH: Meaning, not through droplets at all. Or at least, not through the droplets that fall to the ground. See, we've known for a while that the mouth rain that comes out of your mouth when you talk, the drops come in different sizes. There are the big droplets ...

LINSEY MARR: Kind of larger droplets, you know, that you can see almost with your visible eye or under a microscope.

SARAH: But those aren't the only ones.

LINSEY MARR: Now we know that there are ones that are much smaller than that.

SARAH: That as you talk there's thousands of these tiny air droplets fall out of your mouth.

LINSEY MARR: That really we can only detect using modern equipment.

SARAH: And they're so small, like, sometimes one-fiftieth of a human hair, that instead of falling, they float in these little mouth rain mist clouds.

LINSEY MARR: We now have the ability to, you know, detect viruses in these very small particles in air.

JAD: And have we been able to measure that? I mean, do we know for sure that the virus that causes COVID can travel in those airborne particles? And if it can, do we know how far it can go?

ED YONG: Well, bear in mind that no one even knew that this virus existed until, you know, roughly three and a half months ago.

SARAH: This is Ed Yong, the science writer for The Atlantic Magazine.

ED YONG: You know, in many cases we're sort of starting from scratch but you know, a study came out in the New England Journal of Medicine.

SARAH: In mid-March.

ED YONG: Showing that the virus could remain stable in airborne particles for an hour or perhaps even more.

JAD: Ugh!

ED YONG: Although as many people have pointed out, that was quite an artificial experiment.

SARAH: It was done in the lab, and it just wasn't clear exactly how it applied to real life.

ED YONG: You know, it was evocative but it wasn't a slam-dunk case.

SARAH: But then ...

LINSEY MARR: There was a study that came out—maybe it's just a pre-print still, but they collected air samples at the University of Nebraska, which has one of the hospitals in the US, that's, you know, specially designed for handling dangerous airborne pathogens.

ED YONG: This study by the University of Nebraska Medical Center was really important.

LINSEY MARR: They found virus more than six feet away from the patient. They found it out in the hall.

JAD: Whoa.

SARAH: Wow.

LINSEY MARR: So the virus is definitely traveling that far in air.

JOSHUA SANTARPIA: Well, maybe not. I think that the reality of that situation is that, you know, we were going in and out of the rooms. So the likelihood is that we were bringing it with us when we were going in and out.

SARAH: This is Joshua Santarpia.

JOSHUA SANTARPIA: And I'm an associate professor of pathology and microbiology at the University of Nebraska Medical Center.

SARAH: He's the guy who led this study. And he says that when coronavirus hit back in the winter, for people at his hospital ...

JOSHUA SANTARPIA: It got real, really fast.

[NEWS CLIP: Hundreds of passengers quarantined over coronavirus on the Diamond Princess cruise ship are preparing to leave.]

JOSHUA SANTARPIA: Our first COVID-positive folks came from the Diamond Princess.

SARAH: The cruise ship that was quarantined in Japan back in early February.

JOSHUA SANTARPIA: They asked us to take 13, and it wound up being a total of, I think, 15.

SARAH: In addition to treating these people, Josh and his team went in and swabbed little spots all over the rooms and took samples from the air looking for the virus.

JOSHUA SANTARPIA: I was a little surprised by how much we found.

SARAH: Josh says he doesn't think the virus floated down the hallway on its own.

JOSHUA SANTARPIA: Based on this particular study, it's hard to say how far it went, but we found evidence of virus in and around their entire room.

SARAH: Not only on things people touched ...

JOSHUA SANTARPIA: Their remote controls for their television.

SARAH: But also ...

JOSHUA SANTARPIA: In the air.

SARAH: Just floating around. And landing in all these, like, nooks and crannies around the room.

JOSHUA SANTARPIA: The air handling grates.

SARAH: Under the bed.

JOSHUA SANTARPIA: On the wall. There wasn't a single kind of sample that we took that didn't have some evidence.

JAD: And these are intact viruses that you're finding? Like ready to jump into somebody and make them sick?

JOSHUA SANTARPIA: No.

SARAH: One thing to point out here is that the evidence of virus Josh found isn't, like, actual live virus.

JOSHUA SANTARPIA: Yeah. So it was viral RNA in those samples.

ED YONG: What they find instead are traces of the virus' genetic material which is more like finding the fingerprint of a suspect, which suggests that they were once there at quarantine but might not actually be there any longer.

SARAH: It could be that the virus floated down and then landed on a surface and then disintegrated. Like, we know that the virus eventually falls apart in the environment. But the thing is, like, even if it had been intact, Josh says that he can't really tell yet if the viral spillage that he's seeing around the room is enough ...

JOSHUA SANTARPIA: To, you know, to be capable of causing infection.

SARAH: Like, was there actually enough live virus floating across the room in order to make somebody sick?

JOSHUA SANTARPIA: Yeah.

JAD: Have you made any attempt to figure out how far viruses that could make someone sick can float?

JOSHUA SANTARPIA: So that's the question that I'm currently trying to answer with the work that we're doing now.

SARAH: For now, Josh says he doesn't really know. It seems like it's more than six feet, but is it 10? 15? 20? Nobody knows.

LINSEY MARR: I personally have been using a 10-foot-rule. And the farther, the better.

SARAH: Interesting. Okay.

LINSEY MARR: So if you think about someone who's smoking, when you're close to them, there's the cloud of smoke. But as—you know, as that smoke disperses eventually like 20, 30, 40 feet away down the block it's—you know, it's not a dense cloud of smoke anymore. So the same thing, viruses behave in the same way in the air.

JAD: Oh that's interesting, that gives me a visual.

LINSEY MARR: Yeah.

JAD: That does make me wonder, do you—I mean, do you hold your breath?

LINSEY MARR: I mean, in theory it should help. I've done that when I've run past someone, I'll hold my breath for a few seconds. I don't know if it makes a difference but in theory, it could.

SARAH: The thing that makes the most difference—and, like, every expert I talk to reminded me of this—is just not going anywhere unless you absolutely have to. Don't worry about the six feet, just keep that number as high as you can. And if you do have to leave, and, you know, a lot of people do ...

LINSEY MARR: Just wear a mask when you go out.

SARAH: Because regardless of what kinds of particles the virus can travel on, whether it's droplets or smaller airborne particles—and frankly, regardless of how far it can travel on those different particles, if you've got a mask on, it's gonna stop a lot of those particles from going anywhere. And on top of that, Ed Yong says ...

ED YONG: The masks are not just a medical device, they're also a social device.

SARAH: He says wearing a mask sends a message.

ED YONG: I think the messages that they send depend very much on how many people are wearing them.

AMIL: Okay, podcast people. I'm going to be on your podcast.

JAD: Hey Amil, help me count. How many people in here did you see wearing a mask?

AMIL: I definitely saw one walk by here. So one.

ED YONG: If only one person is wearing a mask in a society that traditionally doesn't wear masks, it's very easy to think "Oh that's a little weird."

AMIL: Seven ...

ED YONG: Whereas, if everyone is wearing masks ...

AMIL: Nine, ten ...

ED YONG: It starts becoming more of a sign that we are all in this together, we want to protect each other.

AMIL: 16, 17, 18. We count ourselves?

JAD: Yeah.

AMIL: Oh. 19, 20, 21. I can see—no wait, 22, 23. Uh, let's see, probably like three—two-thirds or three-quarters, actually.

JAD: Do you think so? Okay, I think that's good. Let's go check out.

ED YONG: Even if that effect is small, I think that is a powerful signal.

JAD: Let's go to number 15. Hey, how are you?*

SARAH: So I think from now on, that's the number I'm gonna start paying attention to.

JAD: I think it's gonna be a little bit like that except it's gonna be for kids and adults. That one's just for kids.

JAD: Producer Sarah Qari. This piece was produced by Sarah with production and editing by Pat Walters. Special thanks to Lydia Bouriba and Julie Fischer for their expertise. And of course Amil Abumrad for his counting assistance. I'm Jad Abumrad. Stay safe, everybody.

[LISTENER: Hello. This is Helen Kim calling from Seoul, South Korea. Radiolab is created by Jad Abumrad with Robert Krulwich and produced by Soren Wheeler. Dylan Keefe is our director of sound design. Suzie Lechtenberg is our executive producer. Our staff includes Simon Adler, Becca Bressler, Rachael Cusick, David Gebel, Bethel Habte, Tracie Hunte, Matt Kielty, Annie McEwen, Latif Nasser, Sarah Qari, Arianne Wack, Pat Walters and Molly Webster. With help from Shima Oliaee, W. Harry Fortuna, Sarah Sandbach, Malissa O'Donnell, Tad Davis and Russell Gragg. Our fact-checker is Michelle Harris. Thanks!]

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