A False Dichotomy: Airborne versus Droplet / Roxanne Khamsi, Lydia Bourouiba

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On March 14, 2020, Roxanne Khamsi published an article in Wired magazine: They Say Coronavirus Isn’t Airborne—but It’s Definitely Borne By Air.

“I wanted to know what airborne meant. What does the word airborne actually mean when scientists and biologists talk about it? Because I detected that there was a debate underlying the debate. In other words, I felt that there were people debating whether it was airborne, but part of me felt that there wasn’t even consensus about what the word airborne meant. And that that could be a huge problem in both scientists talking amongst themselves, but also about the public understanding of the transmission of this disease.” -Roxanne Khamsi

In today’s episode, Dr. Celine Gounder speaks with Roxanne and Dr. Lydia Bourouiba, an Associate Professor at MIT who directs the Fluid Dynamics of Disease Transmission Laboratory. They speak about the difference between airborne and droplet, and what that means for the safety of healthcare workers and the precautions that individuals should be taking. They also discuss the science behind the 6-feet social distancing guideline, which is based on models that predict how far droplets travel in air, and the flaws in these models that may vastly underestimate how far the virus can travel.

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Celine Gounder: I’m Dr. Celine Gounder and this is “Epidemic.”

In this episode, we’re going to talk about research that raises a troubling question: How is the novel coronavirus transmitted? One of the most reassuring things we hear from experts is that it’s not airborne, which we think means you can only catch it by touching something, a surface that’s got the virus on it.

So, you wash your hands a lot and you [00:00:30] think you’ll be okay. But last weekend, Wired Magazine ran a story with the headline: “They Say Coronavirus isn’t Airborne, but it’s Definitely Borne by Air”. It turns out airborne is a very technical term in this context. As the Wired story lays out, researchers who look hard at the details of how viruses travel in the air, stay in the air, and potentially cause infections through the air say there’s reason for concern. I should say at the outset that this doesn’t mean [00:01:00] we should all be panicked about just walking around, especially outside. But people who spend a lot of time in indoor environments with a lot of sick people, like healthcare workers may have a lot to be concerned about, especially because this country doesn’t have a great supply of respirator masks and other personal protective equipment. In the trade, we call it PPE. So that’s a worry for healthcare workers and for anybody who hopes that healthcare workers stay well themselves to care for people who [00:01:30] get sick. I’ve got the author of that Wired story, Roxanne Khamsi, and one of the scientists whose work she explores, Lydia Bourouiba, an MIT professor who directs the fluid dynamics of disease transmission lab.

I’ll start by asking Roxanne how she became aware of Lydia’s work.

Roxanne Khamsi: I mean, I have to say that I have a weird fascination with sneezes. I have had allergies. I actually lived with a dog growing up, my sister is a veterinarian, and I didn’t know until I went to [00:02:00] college that I’m allergic to dogs. So, I spent a lot of my childhood sneezing and having allergies and blaming it on the weather.

So, the fact that her research was about sneezes. It’s a kind of selfish personal reason, but I’m just fascinated with sneezes and, and the idea that you could see this through the lens of physics just wowed me. It just floored me that that people are studying it like that. So, I guess I came to it through a very selfish reason, but now I’m looking at it through a whole different lens of public health.

Celine Gounder: [00:02:31] And then, as I understand it, you were at this meeting in 2015 and you were talking to somebody about MERS at this conference. Tell me a little bit about that conversation.

Roxanne Khamsi: [00:02:43] So I was at this meeting, uh, where scientists from around the world come together and just talk about viruses. And my job in the capacity as an editor and journalist is to go around and talk to people and just see what’s interesting them and whatnot.

And I talked to a [00:03:00] scientist, and I remember we were standing outside in the sun and it was super-hot, and I was scribbling away in my notebook cause that’s what I do when I talk to scientists. And he just kind of, he’s sort of talking about MERS and how people don’t appreciate that it is spread in air in some of the hospital systems.

And, you know, I talk to a lot of scientists all the time. It’s my job. There’s not a day when I’m working that I don’t talk to a scientist. And [00:03:30] every once in a while, you kind of pick up what people aren’t saying but are saying. And he seemed to be saying with this tone that this is something people should pay attention to, that they’re not paying attention to.

So, always in the back of my mind has been this thought with coronavirus, is that, you know, they, they, they haven’t underappreciated airborne nature to them that we don’t fully understand, that we can’t call them necessarily airborne until we know them. But as soon as this new coronavirus came on to our [00:04:00] radar, I immediately started thinking about that conversation, and I immediately started wondering, you know, how much does it behave like it’s cousins, cause it does a different virus.

But you know, if it’s the Brady Bunch, it’s Marcia to Janet. You know, these folks are related, but they’re different. And so, if one of them travels by air, it just immediately got me wondering, are we going to see reports of this being more airborne than we thought? So that’s how I initially got interested.

And so, [00:04:30] um, I guess, you know, Lydia is just really well known in her field. She’s renowned for her work in studying the physics of these, um, violence. What is it called? Uh, Lydia, you had a great title for your paper and I forget.

Lydia Bourouiba: [00:04:44] Violent exhalations, yeah.

Roxanne Khamsi: [00:04:46] Exactly. Violent exhalations, you know, she’s world known for this.

And so, um, I remember, I think there was an article written about her and I just thought, ‘hey, this woman knows about sneezes and she knows about [00:05:00] costs and I want to know what she knows.’ And I’d spoken with some of her colleagues like Lindsay Maher, who’s also very focused on this, and it seemed that there was a consensus amongst people who study the transmission of viruses in the air that something is here that people aren’t really looking at.

Celine Gounder: [00:05:20] Lydia, how did you get interested in studying this of all things? I mean, it seems like a somewhat, um, very specialized area of study.

Lydia Bourouiba: [00:05:28] Yeah. So, the path [00:05:30] was first in applied math and fluid dynamics, but I was in Canada in Montreal, and SARS, uh, as you might may know, hit Canada pretty hard. And I was always interested in, in public health on the side, in addition to pursuing a math and physics training and research in fluid flows.

Um, but when SARS hit, I really realized that I really strongly felt about trying to contribute in, in epidemiology in particular. I joined a lab [00:06:00] in Toronto that was founded, uh, post-SARS for major coordinated efforts in modeling data integration. And what I realized relatively quickly, is that the, the, the top down modeling approaches that we were using in more classical epidemiology, uh, had it merits, but ultimately there was this major gap in scale between that kind of approach, top downs of population modeling, uh, which relies basically on epidemiological data, which often has under-reporting and major gaps.

And [00:06:30] then the research being done at the molecular level, at the pathogen-cell interaction. And there was really a big gap of, of scale, but also communication and, and ability to even bring these two sides of, of the research world together. And it just dawned on me that it was critical to, in fact, link these two sides because we have no way right now to upscale, for example, information gained about a virus infecting one cell [00:07:00] to what happens in the whole host when they’re infected, and what happens to that host in the room, and therefore how is that host affecting potentially others in that room or that building or else? And I realized that those, that scale at the intermediate junction is in fact the scale in which fluids or various forms are involved.

I started seeing the connections, uh, and uh, basically aiming to build a framework that enables us to study these processes.

Celine Gounder: [00:07:29] So Lydia, before we turn more specifically to your research, I’m just curious, you know, you were in Toronto during SARS. Could you just share in a little bit more detail, you know, how that affected you or what you observed, what you experienced during that time?

Lydia Bourouiba: [00:07:43] So I was in Montreal during, I mean, I was between in transition, between Montreal and Toronto during SARS. Uh, and what was really clear was how unprepared we were, and, uh, and, and how quickly [00:08:00] things could really propagate from one side of the world to the other in unprecedented ways.

And, and that really, we were very, very much unprepared. And what was really striking is, particularly once we started, uh, learning more about the events of transmission is that how little we understood about processes that involve that, um, that host to host transmission. But it became very clear that these are notions that we really needed to, to understand, to inform even the [00:08:30] healthcare workers of what they should be doing.

And there was a lot of confusion about, for example, what masks to use. There are different recommendations being given, and studies after SARS have showed that indeed there were, there were events of transmission, for example, even with, um, given the recommendations that were given to the healthcare workers.

And the second, I would say, more than second, the other striking piece was that really the protection of the healthcare workers is critical because that’s where [00:09:00] really the front line is and these are basically the groups that are the most at risk and that we need to keep going. And that’s what’s really very striking.

And so, these lessons stayed with me and framed pretty much all the questions that I think about in my research related to respiratory disease.

Roxanne Khamsi: [00:09:16] And by the way, Lydia, I don’t know if you know I’m in Montreal right now.

Lydia Bourouiba: [00:09:22] I didn’t realize.

Roxanne Khamsi: [00:09:24] But I moved here in December and now I can’t go back to the States.

Celine Gounder: [00:09:29] Roxanne, maybe if you [00:09:30] could lay out like what was the question you were asking in your Wired piece?

Roxanne Khamsi: [00:09:35] So I wanted to know what airborne meant. What does the word airborne actually mean when scientists and biologists talk about it? Because I detected that there was a debate underlying the debate. In other words, I felt that there were people debating whether it was airborne, but part of me felt that there wasn’t even consensus about what the word airborne [00:10:00] meant. And that that could be a huge problem in both scientists talking amongst themselves, but also about the public understanding of the transmission of this disease. Because I have this underlying concern that if we don’t understand what airborne is, when we talk about it, we could go off the rails and see a science communication disaster leading some [00:10:30] people to say, for example, that public health officials are lying because it is airborne and they’re saying it’s not, or vice versa. A huge swath of people saying, chill out, it’s not airborne at all. And I think that I started to detect that neither of those approaches would be truly accurate when one looks at the nuances of biology and physics and things like that. There’s sometimes, um, you know, [00:11:00] a, we want to put everything in boxes right. But sometimes things don’t fall neatly into boxes.

Celine Gounder: [00:11:06] Yeah. So, Lydia, that was actually my next question. And maybe this is what you’re referring to, but what is the difference between droplet, droplet nuclei, aerosol, and airborne spread of disease?

Lydia Bourouiba: [00:11:19] Yeah, so I think that what you were referring to, Roxanne, was the, was the fact that these, these dichotomies between drops and aerosols are, uh, [00:11:30] are basically false, uh, or at least dichotomies means basically false. Uh, so that, that relates to, to your question, Celine, about airborne, aerosols, droplets.

So, this is all basically nomenclature that was, uh, introduced, uh, to, to try to classify routes of transmission. And what do current definitions, uh, entail is, uh, to basically have this very separated dichotomy and, and categorical split between [00:12:00] what we would consider big drops that fall faster than they evaporate, uh, and call that basically drops, but other drops that we would call then something else, in this case aerosols, would be those that in theory would evaporate so, so quickly that they would evaporate faster than they fall. And so effectively the mental images then of isolated droplets that are coming out and some that fall basically very quickly and others that evaporate faster, which [00:12:30] basically stay suspended, and therefore airborne.

And that’s something that has been debated between what, what are the drops that would be airborne versus those that would be large drops, and that has changed throughout history. William Wells was the scientist that really introduced this notion of large drops versus small drops through a series of experiments in the context of tuberculosis transmission in the 1930s.

And, uh, at the time, uh, Wells actually had a lot of pushback from the [00:13:00] medical community in introducing even the concept that things could remain suspended in the air. And so, Wells really was seminal introducing in some sense this, this additional subtlety in this picture to say- well, actually, there are other things that you might not see that are also emitted and they are evaporating faster than they fall, and that’s why you don’t see them on surfaces. And he did series of experiments to show that, to at least support that. Uh, and uh, eventually won. And, and this, uh, this dichotomy, between large drops and small drops or aerosols, which is the word that is being used to, to distinguish them from the other drops, has been introduced. But what is being used to then classify the diseases to say their large drop route, or aerosols is epidemiology data.

Right? So, we’re back to trying to link host-to-host transmission to an epidemiology large population process with the issues of how that data can really be used here, [00:14:00] right? Because we really are not really tracking necessarily, uh, all the movements and observing what these individuals have been doing when we’re linking secondary cases coming from the person.

So, it’s a probabilistic game, which brings us then to the notion of, of distance associated with this classification. And that’s another, um, place where our arbitrary classification and use of numbers is, is also problematic because we’re using these three feet. Uh, so WHO [00:14:30] right now is using a three-feet safety distance to say that, uh, these droplets, or large drops if you will, do not go further than three feet.

Uh, other agencies or guidelines or documentations in Europe or even the CDC are, are using, for example, six feet. These distances are also, uh, computed from, uh, the, the calculation that you would emit isolated again, drops. So, if you will, uh, uh, you know, a ball that is being [00:15:00] thrown out and seeing, well, how far would it go. If it stays in a drop form, how far would it go?

And those models have a flaw that we have highlighted in, in the recent work that they’re not accounting for- um, the actual gas phase that is also being emitted during these exhalations, which is changing completely the range that these drops of all sizes can reach.

Celine Gounder: [00:15:25] So in other words, the six feet distance is not enough. [00:15:30] What are you observing once you take into account the gas phase?

Lydia Bourouiba: [00:15:33] Right. So, in conducting the experiments where we are basically directly visualizing, uh, exhalations both from coughs and sneezes and, uh, also, you know, you know, heavy breathing. What is very clear is that these gas phase that’s coming out in a regime that we call in fluid dynamics turbulent regime. So, it’s basically high momentum. It’s really a lot of energy during these exhalations. So, it’s not that smooth air breathes. Concretely, what we, in [00:16:00] fact, not only predict with the modeling, including the cloud, but visualize directly, is that the whole cloud and its payload can, can move coherently. So, in a concentrated manner, uh, up to distances of seven to eight meters, for example. So that’s about 20 to 26 feet, uh, for example, from, from, from a sneeze. For coughs, it’s a little bit less. But it’s certainly way more than the three to six feet.

Celine Gounder: [00:16:26] I mean, what you’re saying is really alarming to me because that’s how we have [00:16:30] planned our infection control practices. There was a paper that was just published in the New England Journal of Medicine on aerosol and surface stability of the coronavirus, uh, the SARSCoV2 coronavirus., and those researchers found that the virus could remain viable in aerosols for the duration of their experiment, which was three hours. So how do you integrate that with what you just [00:17:00] told me in terms of concern for healthcare worker risk.

Lydia Bourouiba: [00:17:03] Right, and this is a really key point because the, the, the, the physics that we are deriving from visualization tell us at least how far things go and that they stay coherent. Now the other key piece, of course, is where are the pathogens in there and how long they, they persist. And that’s why these kinds of studies to also look at the, at the duration of persistence are so critical. And, and so the way that you would integrate those is to really integrate the [00:17:30] notion of, of distance and concentrations with time to be able to get a sense of risk of exposure in a given space. And of course, that becomes a little bit specific to which phase you’re in. If you are in a negative pressure room with high air changes, then the risk of exposure after X amount of time would be different than that if there is basically none of that.

But ultimately at this point, the recommendation that, that would be the most conservative in [00:18:00] terms of, of risk management would be to have respirators if you enter the room.

Celine Gounder: [00:18:05] So, I guess one question I have then is, you know, we’re looking at hospitals being full of patients with coronavirus. Uh, if they, if they’re not already, they will be within the next week or two.

Why is it at all safe for healthcare workers to be in a hospital full of coronavirus patients without personal protective equipment at all times?

Roxanne Khamsi: [00:18:27] If I can just jump here, Celine, and mention [00:18:30] some things that have been concerning to me and I, I, I think I have tried to raise this question because it’s something that I, I do sit with and wonder.

I, I worry about people like you who are on the front lines, people who are medical workers. And I worry whether some of the lessons from SARS are being forgotten. And that’s not a inconsequential thing. And so, one thing that comes to my mind is that [00:19:00] there’s a close cousin of the new coronavirus that cropped up some not so long ago called Middle East Respiratory Syndrome, or MERS. And in a study that scientists did following these outbreaks, they found that there was a 35-year-old man in style in South Korea during one of these outbreaks of MERS. And he was in the ER, in the hospital, and about 1600 people were in his [00:19:30] vicinity, the scientists calculated over the course of time that he was in his hospital. And he infected 82 people, and 33 of those people were patients, 41 of them were visitors, and eight of them were staff, in the course of this ER visit. And um, you know, obviously there was overcrowding, but it points to me that these coronaviruses, they might not just be about touching surfaces or touching your [00:20:00] face, and that there is an aspect of them that we might be overlooking, and that might be placing healthcare workers at risk.

I mean, I’m speculating here because the data has not proven this for the new coronavirus, so I have to be careful to mention that. And I’m not a scientist, I’m not a doctor. But I am somebody who’s looked at the literature and just wants to know the answers to these questions.

I don’t know if, uh, you know, other people would agree, but it’s a concern to me. And we could also talk about what happened at [00:20:30] some of the residential complexes with SARS and with this new coronavirus, where sewage, uh, sewage traps or sewage plumbing that wasn’t quite great seems to be the cause of the spread of these pathogens. So, I think that the implications are, could be pretty large.

Celine Gounder: [00:20:50] So you’re referring to the Amoy Gardens apartment building, I believe. Lydia, maybe if you can explain to us what happened in that building.

Lydia Bourouiba: [00:20:59] I mean, as Roxanne mentioned, they suspect that the contamination was due to this, to this failure in the trap.

These traps, that’s how we prevent odor. You have this clear liquid that is basically covering up for the sewage that is going through the different pipes from other locations. And there was a failure that led to the aerosols generating from that, from that water to be basically contaminating the other units.

Celine Gounder: [00:21:23] So Lydia, let me ask you this. So could flushed toilets, whether in the hospital or [00:21:30] just in a public restroom, be helping to propagate this?

Lydia Bourouiba: [00:21:34] So at this point, I would be very careful with that because there is evidence that the viruses in the stools, um, but it’s not clear that that is really a, an event that would have dominated the routes of transmission that we have seen.

The physics of, of high-pressure flushing generates drops that are contaminating surfaces and air, and that’s clear, but whether the load in those drops is [00:22:00] significant, it’s not clear. There’s really not much evidence to be able to support, you know, bold claims about that.

Celine Gounder: [00:22:06] So there are different medical procedures that can generate aerosols like bronchoscopy, which is when we look down into somebody’s lungs, or ventilation. What are some of the other common things, whether it’s in a healthcare setting or elsewhere, where you might be generating aerosols like this?

Lydia Bourouiba: [00:22:25] Yeah, so definitely the procedures that are very much [00:22:30] aerosol generating include also, you know, intubation. Uh, and that’s going to be the procedure that is going to be very much required for treating the worst cases, right? We really need to be thinking about what kind of PPE the staff will use and how many people can be in there and, and for how long.

And, and the other side of that is, well, are there other procedures that are aerosol generating that we might want to scale [00:23:00] down if they’re not absolutely necessary?

Celine Gounder: [00:23:02] Given what we know about the fluid dynamics, and given that we know that the coronavirus can survive aerosolized for at least three hours, why is it okay for a healthcare worker to be working in a hospital full of coronavirus patients at all without personal protective equipment on them at all times?

Lydia Bourouiba: [00:23:24] Yeah. That’s something that is making me very, very nervous.

Celine Gounder: [00:23:28] The CDC recently issued [00:23:30] guidance on its website on quote “strategies for optimizing the supply of face masks.” It has downgraded its recommendations on what masks to use from N95 respirator masks to the loose fitting surgical masks, which are really designed to protect against splashes and sprays in the operating room, and also to prevent sick people from coughing and sneezing infectious particles into the air.

The CDC goes on to say that healthcare workers may reuse their face masks several times if they’re in short supply, and even use [00:24:00] homemade masks like bandanas and scarfs if they run out of face masks. I mean, wow, bandanas?

Lydia Bourouiba: [00:24:07] So the, this dichotomy between these large drops and aerosols is really at the root of, of, of what is driving these, these policies, right?

And that’s what fundamentally needs to change, because if we remain stuck in this, uh, buckets, as, as Roxanne said, uh, view, uh, or, or basically very rigid dichotomy then there is this belief that after three feet, [00:24:30] these large drops are not a risk, and therefore you can walk around with no PPE, even up to three feet or six feet from the person.

And so, I think it is really time for to realize that although convenient, because of course we want to put things in boxes and in categories, and having two of them is, is easy to communicate. And although of course relaxing that statement, it’s saying not everything is just large droplets so a three feet can use some level of concern, but this is [00:25:00] not about the general population.

This is really about making the right decision at the front line for the healthcare workers, given the, uh, the, the, the room configurations and, and the procedures that really might, um, even if it’s not intubation, might require to really be wearing N95 respirators at all times. And, and from the research that I do and the literature that has been published about persistence so these survivals and the fact that, you know, we have [00:25:30] direct visualizations of these cloud laden with droplets, and again, by droplets here I mean all droplets, not just the large one that fall at three feet, all continuous size drop distribution that is trapped in a cloud and carried forward. I mean, these, these recommendations are not in line with the science.

Roxanne Khamsi: [00:25:49] So my story went online on Saturday, and then a couple of days later, things changed. This is evolving fast. The WHO, kind of, was more vocal about [00:26:00] how it might be airborne and, uh, said that the, you know, respirators should be used for these procedures. But what I wonder about is, is supply determining policy rather than science? And cause there’s a, there is a lack of supply or lack of availability.

There is a lack of availability of proper respirators, as far as I understand. And what I wonder is, okay, so if the WHO is saying you need a [00:26:30] respirator for these procedures that we know aerosolize this stuff, what about if you’re a doctor seeing somebody who’s coughing a lot and you’re just given a surgical mask? Is that enough? Like, I would have to obviously defer to the experts, but it’s a question that I have, and I think it’s a question that needs to be addressed.

Celine Gounder: [00:26:54] So, to provide a little bit more context, many of the hospitals in New York City have now [00:27:00] run out of, or have very limited supply of the N95 respirators.

And so, as a result, healthcare workers are seeing patients with the loose-fitting surgical masks rather than the respirator masks. And for people who are listening, just as a reminder, the respirators are the tight-fitting masks that really are meant to filter air from the outside in, whereas the surgical masks are what we put on patients so that they don’t contaminate the environment around them when they sneeze or cough.

So [00:27:30] Lydia, you know, hearing that healthcare providers are wearing surgical masks, not respirators. And knowing what you know about the fluid dynamics and the infectiousness of, of the aerosols, what would you say to that?

Lydia Bourouiba: [00:27:43] Yeah, so this is, this is a problem. Uh, I, I mean, at this point, as you mentioned earlier, we’re not at the point where, you know, the hospitals are at over capacity, but we will most likely get there at some point. And, uh, and [00:28:00] this is problematic. And, and, and in part, and this is not to, again, you know, stoke fear or else, but I think that’s where the decision-making and, and how it’s done and based on what is so critical because, as Roxanne mentioned, if it’s really driven by, um, shortage and therefore we are adapting your condition based on shortage, then that’s really doing things in some sense, upside down, right?

But because the risk clearly from what we have seen from these exhalations and from the rapidity [00:28:30] of spread of this, uh, is, is, is really calling for respirators, and if that’s what’s needed instead of, I mean, of course, if we have no choice, then you know, it’s sort of war times you do with what you have.

But that would mean that one of the highest priorities besides diagnostics and of course developing vaccine that we would have in in a year or two, is production of alternatives and high-grade respirators. And, and diverting immense resources to make [00:29:00] sure that we have that kind of PPE ready and, and that’s, and that decision would start by understanding and accepting that this dichotomy is not necessarily what should be driving these decisions, the decisions right now, and that even if you wanted to stick with this dichotomy between large and small aerosols, there is just not enough data to say that this falls even in the bucket of the large drops, right, of the droplets. So, so, so that’s why, that’s why it’s so, so important to have clarity in [00:29:30] these guidelines because they really affect that kind of decision making and at this point, I think that this is, this is a mistake. We should have a recommendation of respirators to the, to the healthcare workers, particularly when we can have a surge of covid patients coming in and swamping the hospitals.

Celine Gounder: [00:29:51] In the absence of that, I’m thinking back to, you know, I was in West Africa during the Ebola outbreak, and you know, patients were in [00:30:00] some of those Ebola treatment units essentially being treated actually outdoors, and you would have this plastic sheeting, but it was essentially outdoor tents.

Um, I mean, is that the kind of thing we need to be entertaining in the absence of appropriate PPE for healthcare workers?

Lydia Bourouiba: [00:30:15] Absolutely. I mean, of course the first choice is to get the right PPE. If in any case the hospital is at full capacity and, and even if it’s not, I was talking this morning with a city mayor and, and what I was saying is the testing being [00:30:30] done outside, for example, even for the screening is, needs, needs to happen.

It shouldn’t be done, you know, by some kind of triage staff inside because it’s a huge amount of individuals hopefully when we’ll get enough tests and they are functional, that are going to come through and these should be done in another location from the hospitals so that we’re not also exposing, because of testing, the the, the other patients and healthcare workers in particular in the, in the hospital setting. And in the [00:31:00] hospital setting if weather permits, then having these kinds of natural ventilation ad hoc solutions, either by expanding outside or retrofitting quickly, certain designs of windows, like done basically in, in, in poor-resource locations around the world, uh, would be a priority.

Celine Gounder: [00:31:18] Roxanne, you’ve been looking into classic studies of infectious disease transmission, um, and whether these diseases are airborne. I know you dug up a study about airborne flu, quote [00:31:30] unquote, on a plane. Can you talk a little bit about that study?

Roxanne Khamsi: [00:31:32] Yeah, absolutely. Donald Milton, who is a researcher in this space as well, pointed me to this debate about whether influenza, you know, the flu is airborne and how he still feels like he’s trying to convince folks all these years later, you know, a century after the Spanish flu that influenza can be considered, you know, truly an airborne disease or how airborne it is. And he noted that [00:32:00] there was this kind of interesting and intriguing example of a plane that was grounded on the tarmac for three hours in 1979 and interestingly, the ventilation system has broken down, or is not opera operational, as they’re kind of trying to address this engine failure and trying to figure that out. And meanwhile, there’s somebody that’s on the plane sick.

Lo and behold, three days later or within three days, 72% of the 52 passengers on that flight were sick, and [00:32:30] most of those tested for the flu tested positive. So, the idea is, is this one person on the flight, infected like three quarters of the people on the flight in this three-hour window, or at least in the course of the flight, exacerbated by this three-hour window in which the ventilation was caput.

And yet, we’re still here in 2020 with people kind of debating how airborne fluids, and I’m, I’m sure that Lydia could speak more to that debate, but it was really intriguing to me [00:33:00] that this bizarre story from the 1970s wasn’t convincing enough to most people.

Lydia Bourouiba: [00:33:06] Yeah. I think this is, this is a great point. I’m glad you highlighted this because that’s where you have these almost ideological blocks, right? And that has repeated itself in, in scientific history multiple times. Now we’re talking of course, about this particular concern of, of public health, but ultimately becomes you know, the dogma, right? And so, and, and, and I want to put this in perspective [00:33:30] and return to the story of Wells because in some sense it’s the same dogma, uh, that is still sort of there. And he received a lot of resistance from the medical community, and, and was ridiculed, uh, by the medical community at the time with this idea that it was everyone from in, in the context of tuberculosis he then managed to really establish that very clearly. But for, for SARS, for example, that was also a debate and MERS as, as we mentioned earlier in this discussion, that’s was also a debate. And [00:34:00] even for TB, tuberculosis, you can find still some pockets of the communities that still debate this.

And, and I think it’s something that, if anything comes out that is good out of this, I really hope that we’re going to break through this because that’s when we’re gonna get out of these dichotomy that is again, false dichotomy of large drops versus aerosols that is blocking us in, and keeping us in something behind in the 1930s even though we’re in 2020. So I, I think these debates are, [00:34:30] are inherently in some sense, uh, dogmatic and, and the only way that you can, that you can break that is to have the science and the measurements and enough of us that just continue to persist doing this kinds of research so that we can finally just quantify and put the same efforts as we put in all the other areas of medicine and basically infectious disease.

Celine Gounder: [00:34:51] So I’d be curious to hear what you guys think, each of you. Would I be wrong in saying that if I am a healthcare worker, [00:35:00] um, working in a hospital full of coronavirus patients that I should be wearing, an N95 respirator at all times?

Lydia Bourouiba: [00:35:07] My answer would be yes.

Celine Gounder: [00:35:08] That, that, that would be correct for me to do that.

Lydia Bourouiba: [00:35:10] Yes.

Roxanne Khamsi: [00:35:12] And our health systems should say to anyone who has power to move production forward or to intensify production of these respirators, like, why isn’t that happening? Or why hasn’t that happened? What can we do to help the situation so that there isn’t shortage going forward?

Celine Gounder: [00:35:31] So, I have to admit, I am, I’m really anxious. Not that I wasn’t already, but I am really concerned having had this conversation with both of you, and just in the time that we’ve been talking, I’ve actually gotten two text messages, um, from colleagues in other cities asking me, um, is it safe for us to be wearing a mask only some of the time?

Is it safe for me to be wearing a surgical mask and not a N95 mask when I’m taking care of these patients [00:36:00] and, um, I’m going to be getting back to them and I’ll be telling them that they should probably be wearing an N95 mask all the time.

Roxanne Khamsi: [00:36:07] Yeah, Celine, I’m worried. Please stay safe yourself.

Lydia Bourouiba: [00:36:11] Yeah. Thank you. Thank you so much for this, this is very important.

Celine Gounder: [00:36:17] This morning, my old college buddy Rick Corcoran, reached out with a question. It relates to the conversation we just had here.

Hey, Celine, it’s Rick. I’m wondering about masks. Should the general [00:36:30] public be wearing the masks that I’m seeing on the street, and if so, do I have to get one of the official N95 models, or can I just get one of the lighter duty ones, like from Home Depot? I’m hearing conflicting reports. Thanks.

Celine Gounder: [00:36:45] I hear you, Rick, you’re worried. You’re worried about Alexa and your daughters, but here’s the thing. Many hospitals have already run out of N95 masks. We’re wearing surgical masks. Those loose-fitting masks, and the CDC is now [00:37:00] telling us that we may have to wear bandanas and scarves in the hospital to protect ourselves.

The general public has the option to stay home. We don’t have that option. We have to go into work to take care of all of you. Staying home is a much more effective way of avoiding infection than wearing a mask. So please, if you have in N95 respirator masks home, please reach out to the healthcare workers in your life and donate those masks to those who need the most.

Drop them off on their [00:37:30] doorstep outside their home. The health system is already overwhelmed. The more of us who get sick, the worse that situation’s going to get. More people will die from coronavirus and more people will die from all the other stuff they get sick with. Rick, stay safe and be well. I’m thinking about all of you.

Epidemic is brought to you by Just Human Productions. [00:38:00] Today’s episode was produced by Dan Weisman and me. Our music is by the Blue Dot Sessions. If you enjoy the show, please tell a friend about it today, and if you haven’t already done so, leave us a review on Apple podcasts. It helps more people find out about the show.

You can learn more about this podcast, how to engage with us on social media, and how to support the podcast at epidemic.fm. That’s epidemic.fm. Just Human Productions is a 501(c)(3) nonprofit organization, so donations to support our podcasts are tax-deductible. Go to epidemic.fm to make a donation.

Starting next week, we’ll be releasing “Epidemic” twice a week on Tuesdays and Fridays, but producing a podcast costs money. We’ve got to pay our sound engineers. We’ve got to pay our producers, so please make a donation to help us keep this going.

Also, check out our sister podcast, “American Diagnosis.” You can find it wherever you listen to podcasts or at americandiagnosis.fm. On “American Diagnosis,” we cover some of the biggest public health challenges affecting the nation today. In season one, we covered youth and mental health, in season two, the opioid overdose crisis. And in season three, gun violence in America.

I’m Dr. Celine Gounder. This is “Epidemic.” [00:39:30]

Lydia Bourouiba Lydia Bourouiba
Roxanne Khamsi Roxanne Khamsi
Dr. Celine Gounder Dr. Celine Gounder