Ep. 24: How COVID-19 Really Spreads

COVID-19Science
Written By Christopher Shulgan

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Is the COVID-19 virus really able to waft about on tiny aerosol droplets for tens of metres through HVAC systems? How possible is it to catch the virus from an elevator button or a playground slide? Lots of people have lots of worries about catching COVID — but how is it really transmitted? To find out, guest host Dr. Peter Nord, chief medical officer of Medcan, interviews two experts: Queen’s University medical school infectious disease chair Dr. Gerald Evans, and Rutgers University virologist Dr. Emanuel Goldman.

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Please subscribe and rate us on your favourite podcast platform. Eat Move Think host Shaun Francis is Medcan’s CEO and chair. Follow him on Twitter @shauncfrancis. Connect with him on LinkedIn. And follow him on Instagram @shauncfrancis. Eat Move Think is produced by Ghost Bureau.

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COVID-19 Transmission Myths final web transcript

CHRIS SHULGAN: Remember that open letter to the World Health Organization that raised such a stir? The one signed by 239 experts from 32 countries? It called on the WHO to recognize the potential for airborne transmission of the virus. It talked the potential for the virus to be carried by tiny, aerosol microdroplets that could travel tens of metres. If airborne transmission really is a thing, then why are so many of us only practicing two metres of physical distancing?

CHRIS SHULGAN: But here’s the thing—very few of the news reports about that letter mentioned that those 239 experts were mostly from non-medical disciplines. If you look at where they're actually from, they're engineers and chemists, they're experts in air flow mechanics. But there are not a lot of MDs on that list. And if you talk to the people who study the way viruses actually infect people, many of them were puzzled by this letter. Because an enormous amount of evidence already out there suggests that airborne transmission of COVID-19 is not really a problem. Like, theoretically it’s possible, but if COVID actually was airborne, the experts say that infection rates would be orders of magnitude higher than what they actually are.

CHRIS SHULGAN: That letter is just one of the reasons we made this show about COVID-19 transmission myths. Our guest host today is Dr. Peter Nord, Chief Medical Officer at Medcan, who advises some of Canada’s biggest organizations about how to navigate the pandemic. One of his interview subjects today will discuss the latest evidence on the way COVID-19 spreads on inanimate surfaces like countertops. Now, though, we’ll start the show by investigating the practicalities of the way COVID-19 spreads through the air. Here’s Dr. Nord speaking with Dr. Gerald Evans, a professor and the Infectious Diseases Chair at the Queen’s University School of Medicine.

PETER NORD: So Dr. Evans, how did you choose this particular specialty in medicine?

GERALD EVANS: Well, it is kind of interesting. There's a number of things that influenced me. I was very interested in microbiology as a young fellow, and I read biographies of famous people like Louis Pasteur and Robert Koch and others who were the sort of pioneers in microbiology and understanding human infectious diseases. Once I got through medical school and I was in my residency, I was always struck by the limitations that some sub-specialists have by organ systems. If you're a cardiologist you study the heart, if you're a respirologist you study the lungs. And I kind of liked the way infectious diseases kind of continued to look at the person as a whole, and really in all honesty, infectious disease people always seem very smart because we have to maintain a very general knowledge of a lot of systems.

GERALD EVANS: And so I.D. was very attractive to me from that aspect. And then the funny link about all this is that years ago when I was a medical resident looking at ideas of specialty, I actually wrote to Dr. Tony Fauci at the N.I.H. and was interested in whether I could have a fellowship down there. And then—he is an amazing guy. He—this is the days before the before emails, he wrote a letter back to me and said, you know, you should continue to pursue this career. It's exciting, it's going to be interesting. And was very encouraging and suggesting that it was great. And actually I recall now, having looked at the letter that he said, you know, keep in touch and tell me how things go. I never corresponded with him again after that. And I ended up doing infectious diseases out at the University of Calgary in Calgary, Alberta. And really, those sorts of things were the things that sort of drove me into this specialty. And lo and behold, it pans out that it's kind of an important specialty in this day and age.

PETER NORD: The rock stars of the time. Who thought—who would ever think that I.D. and public health would be the rock stars of healthcare?

GERALD EVANS: Although I'm always reminded of Andy Warhol's thing, at least that was attributed to him, that everybody's famous for at least 15 minutes in their lives or something or 15 seconds. So maybe my time is here and it'll disappear quickly.

PETER NORD: Dr. Evans, we've heard and read so many headlines over the past months about droplet versus airborne, surface contagion, and even most recently 200 scientists signing a petition to the World Health Organization about transmission distances. In your view, what are some of the main myths regarding COVID-19 transmission?

GERALD EVANS: I think the biggest myth at the moment, or at least one that's really having a hard time getting put to rest is the issue of what the contribution is from airborne or what's sometimes referred to as aerosol transmission. And this has always been a concern with respiratory viruses, because we do know that some viruses can be transmitted in an aerosol and therefore are airborne. And that, of course, leads to higher infection rates and concerns that way. So that's probably the biggest one.

PETER NORD: So there's certainly—you mentioned speculation. What do you think is going to help that? Are we waiting for more evidence, more research? Are there studies going on in this area?

GERALD EVANS: I think there's still a lot of interest in trying to do some studies within the whole concept of airborne and aerosol, but I should say that, you know, we've got some fairly substantial good epidemiologic data which tells us that the primary route of transmission, the most effective, and the dominant route of transmission is actually large respiratory droplets. And that's led to what all the current recommendations are all about. That is maintaining physical distance from someone, use of masks, etc. And we know that because we know that if this was actually an airborne or aerosol-transmitted virus, you know, dominantly, we would be seeing easily 10 to 20 times as many infected people around the world that we are currently seeing.

GERALD EVANS: And yes, you know, people then get into the issue of well, you're not capturing everybody you're seeing because some people may not present with overt symptoms, etc. But, you know, we know a lot about the reproductive number of viruses that are transmitted through an airborne route. And those are typically, you know, reproductive numbers of around 15 to 18. Measles is 18 as an example. And this virus really has a natural reproductive number of about 2.3 to 2.4. So it really is behaving a lot like a droplet virus, much like influenza is. And that's where it really tells us that if airborne transmission's occurring, it's occurring extremely uncommonly. And it is certainly not the dominant form of transmission for this virus.

PETER NORD: Yeah, there was a study that came out of China a couple of months ago that was quoted heavily in the literature, and mostly the headlines that got a lot of press about this whole aerosolization. I look back at the study, and I was a bit surprised that even within the study that the authors were commenting on some of the qualifiers embedded in the study, maybe you could comment on that only because it got a lot of headlines.

GERALD EVANS: Yeah. I mean, there have been a number of them, and one of the interesting things is that they seem to pop up about once every 10 days. And some of them are based on studies, like the one that you're talking about. And inherently the issue there was they were looking for evidence of virus in different areas around hospitals and in public places in a city in China. And ultimately, although they could discover what seemed to be viable virus in some concentration in spaces that you would expect to be heavily contaminated, you know, the evidence that just because you can find the virus or viral RNA in an aerosol doesn't necessarily mean it's an effective means of transmission.

GERALD EVANS: And that's where I think the conversations have to happen between people like myself who deal with infections and people who study aerosols in airborne or fomite transition. It's just because there's a virus there doesn't mean that it's actually an effective means of transmitting the virus. And a lot of studies have been flawed by the idea that they've used detection of viral RNA, which is not actually looking for the virus itself, it's looking for a component of the virus, and implying that if they can find the RNA, that must mean there's virus there and therefore the virus there must be able to infect people.

GERALD EVANS: And I think the biggest challenge that we're facing at the moment is we still don't know—and this is actually applicable to all of the human coronaviruses that we study, we don't know what what's called the ID-50 is, and that's the infectious dose required to infect 50 percent of people. And that tells us how much virus you need to actually cause a transmission event to occur. And that's never been well worked out for most of the coronaviruses. So in that absence, simply finding a bit of virus on a surface or finding some virus in an air sample, and and I can tell you, there's studies that have looked at air sampling and haven't found anything and others that have, we really don't know what its contribution is to the transmission of COVID-19.

PETER NORD: Yeah, I think that's obviously where some of the evidence like you say is lacking and that has really been, I think, what was behind some of the qualifiers that we've seen in the literature, and that maybe have led to that most recently over 200 scientists signing a letter, sending that to the WHO about, you know, distances, and it's more than two metres. Maybe you could comment on what was behind that? I found that particularly interesting, and of course as you said, about every 10 days there's something that comes up. And I think that was about 10 days ago or so. So maybe you could comment on that.

GERALD EVANS: Yeah, that was an interesting letter. And, you know, I think it's important to point out that, in essence, what the authors were getting at, and the scientists who signed it, although some of them are microbiology colleagues that I know, including one here in Canada for sure, what they were arguing was was that there's a potential for airborne transmission. And I guess my response to that is there's always a potential in any respiratory virus if you were to create an infectious aerosol that you could transmit it.

GERALD EVANS: And so the gist of that article was is they just wanted the WHO to recognize that there was a potential or the possibility of transmission. So there's the qualifier on it. It is not the dominant mechanism of transmission. And there was an unfortunate paper that was about seven days before that paper or 10 days, that suggested that it was the dominant form. And that I think is way off base. The other thing is, is that this group was really a group of scientific colleagues, science colleagues in different specialties, physics, some of them were in engineering, there were architects and there were chemists. And they study aerosols. So they know about aerosol distribution, they understand the dynamics of aerosols. The question is, is that aerosol that's drifted, you know, a distance from the patient, is there sufficient virus there to actually cause infection? And there's a mechanistic point of view that argues that it isn't. And that's because these little tiny droplets, what's unique about them is that they bypass the normal filtering capacity of the upper respiratory tract.

GERALD EVANS: So small droplets, the reason they can be infectious for things like chickenpox and smallpox and measles is that they can bypass those defences, get into the lung, and then they set up an infection there, which leads to viremia and other things. So we know that the target for this virus is actually the upper respiratory tract. So if you want to effectively transmit this virus, you probably need to be in the form of a large droplet, which is what we're arguing is the dominant mechanism, because those are actually filtered in the upper respiratory tract, and they settle there. And that's where the cell receptor that allows the virus to attach to a human host and lead to cell infection occurs. So there's lots of reasons why yes, you know, you can argue aerosols are potential and possible, but it's a very unlikely and certainly not a characteristically dominant way for this particular virus to infect people.

PETER NORD: That's really helpful. Dr. Evans, just for the benefit of our listeners, can you tell us what is the upper respiratory tract?

GERALD EVANS: So generally speaking, we define the respiratory tract, differentiating upper from lower at around the level of the larynx, which is your vocal cords, your voice box. Below that is the trachea and the lungs and the airways and above that is your oropharynx, that's the back of your throat around where your mouth is all the way up to the nose, and of course, includes the nose and the mouth as well. So it's the sort of cut off at about the level of the voicebox, the larynx that we define. Above that it's upper, below that it's lower.

PETER NORD: So what advice would you give policymakers, based on the scientific evidence that we now have about COVID-19 transmission?

GERALD EVANS: Well, I think we're on the right track in terms of what we're doing now with policies around universal mask-wearing out in public, particularly in indoor spaces, because that does help to prevent large droplet transmission. There's no question about it. It argues that, you know, we don't have to excessively worry the public in general about having to have huge amounts of changes in how we go about our normal day-to-day business. So it does allow for the concept of reopening and opening up the economy in a careful, select manner, because we don't have to necessarily worry about that airborne transmission. Because airborne transmission, like I said, it has a much higher reproductive number and would suggests that, you know, we would see billions of people on the planet infected very quickly versus the millions that we're currently looking at.

GERALD EVANS: So I think that's probably one of the main issues is that what we've been doing so far with the public health measures of social distancing, avoiding crowds, wearing masks, those are all the right policies and they're going to have an effective means of controlling transmission of this virus as we try and return society in general to a sort of more normal or slightly—you know, the expression we use is the new normal state. But that's really where I think where it hits the policy question.

PETER NORD: Interesting. And just to carry that forward, let's scroll forward a year from now, what do you think the public's perception of COVID-19 will be 12 months from now? What kind of are the behaviours are going to be like, if you had to prognosticate?

GERALD EVANS: Yeah. Well, I think we're learning very quickly now, with the resurgence that's been seen, of course devastatingly in the United States, but even here in Canada, that some of this reemergence of the virus into what could become a second wave is being generated by young people. And so I think with that understanding, I think what we're going to look for in the future is people recognizing that all spectrum of society based on age and other factors are all really relevant to the reducing the circulation of the virus and preventing people who are more susceptible from getting infected. So I think the public will eventually embrace this. And unfortunately, it's going to come at the expense of recognizing that people who either feel excessively okay with returning everything back to the way it was, is not exactly the right answer.

GERALD EVANS: On the other hand excessive fear, which still exists in a large segment of the population, I think can be tempered when we recognize that the things that we are doing with testing, contact tracing, mask-wearing, maintaining social distancing measures and all that, do have a measurable effect on controlling transmission of the virus until we have an effective preventive measure like a vaccine.

PETER NORD: That's terrific. Obviously, we've learned a lot over the last six months or so. It'll be fascinating to see what the next six to 12 months is going to look like. And maybe we can have you back on in six to 12, and we'll check we'll compare notes at that point and see how close to being accurate we were.

GERALD EVANS: Yeah, I'm always worried. It kind of reminds me either of astrologers who predict the future and get it wrong, but have a reason because the Saturn was in the wrong house or something. And even worse, political predictors who oftentimes get things wrong. But I think we got some good science here to base it. And we're definitely learning a lot. I recently said, we're going to learn so much about viruses and viral pathogenesis when it comes to coronaviruses in the next few months that would have taken us decades to learn. So I think that might be the slight, tiny silver lining in this otherwise black cloud.

PETER NORD: Terrific. Okay. Well, thank you so much for your time. Very interesting. And we'll definitely follow up in six to 12 months.

GERALD EVANS: That'd be great. I look forward to it.

CHRIS SHULGAN: That was Dr. Peter Nord speaking with infectious diseases expert Dr. Gerald Evans about transmission of the virus through the air. Next, we have a scientist who we sought out because he wrote a comment for The Lancet on the mechanics of COVID-19 transmission from inanimate surfaces. Here’s Dr. Nord speaking with Dr. Emanuel Goldman, a professor in the Department of Microbiology, Biochemistry and Molecular Genetics at Rutgers University’s New Jersey Medical School.

PETER NORD: Dr. Goldman, for the benefit of our listeners can you introduce yourself and tell us a bit about your background?

EMANUEL GOLDMAN: I did postdoctoral research at the Harvard Medical School and then at the University of California at Irvine. At Harvard Medical School, I spent about four years working on animal viruses, so I actually have some knowledge, some firsthand experience working in animal viruses, and my PhD work was in bacterial viruses or bacteria phage. So I consider myself a virologist.

PETER NORD: Perfect. Well, what prompted you to recently write the comment about COVID-19 transmission in The Lancet?

EMANUEL GOLDMAN: Well, like everybody else I'm very concerned about this pandemic, this major impact on our lives and our health. That alone probably wouldn't have prompted me to write this comment, but my mother in law was driving me crazy. She lives with us and she's, you know, can't touch the handles of the food delivery person or, you know, she was worried about all kinds of transmission from objects. And I can't blame her, because the public advice was that as well.

EMANUEL GOLDMAN: It's just as a virologist and a scientist, it didn't make sense to me. I knew the coronavirus was an enveloped virus. Those are even more fragile than other viruses, which are just protein-coated. So I decided I was going to look at the literature to see what this was based on. Is it really evidence-based?

EMANUEL GOLDMAN: And I was fortunate that in 2020, a research team had published a very extensive review on this issue. And while I was in that process, a new article came out subsequent to the review having been published, and that was in the New England Journal of Medicine, and that got a lot of attention in the press. And that article appeared to confirm the transmission or the risk of transmission of coronavirus from fomites.

EMANUEL GOLDMAN: For people who don't know, the word "fomite" is a fancy word that means surfaces or objects, inanimate objects. And as the famous saying goes, the devil is in the details. The starting input inoculum—that is, the amount of virus used at the outset—was humongous. It was huge. And over time, there was a great decay of the virus. But because they started out with such a huge amount, they were winding up with virus that they could see the endpoint, which was days later. And that struck me as being unrealistic, to put it kindly.

EMANUEL GOLDMAN: So I said, "Well, what would be realistic?" If you start out with 10 to 100 virus particles in a droplet and that droplet is now deposited on some fomite, on some surface, the question is how much would you expect after a day, two days, three days? And the answer? My answer is none. You wouldn't expect any, because of the decay of the virus. There was one paper with the original SARS, the one that was detected at the end of 2002 and caused the first SARS pandemic, and that paper attempted to measure the survival of virus on fomites in what would be a more realistic scenario. That is, they took smears from actually infected patients and put them on the fomites, and then looked to see how much virus is left. Well, it turned out there was no infectious virus left after a relatively short period of time. Hours. They found the viral RNA, but that's not surprising because the virus had been there when they started out. In fact, that's the control. It reassures you that they actually did the experiment correctly. They did start out with virus, but there was no infectious plaque-forming units of virus after a few hours.

EMANUEL GOLDMAN: And so this is what prompted me to write the article. Well, that was one part of it. The other part of it is that public policy was being driven by these recommendations and this data. The New York City subways, which had never been shut down in its entire hundred-year history was shut down at night to clean the subway cars. All kinds of ways that public policy was being driven by these recommendations based on these experiments. And the experts were just taking the data at face value, and not looking in depth into what the data—the basis for the data. And that was the other thing that motivated me, because I realized that so much of these recommendations are counterproductive. They're focusing on the wrong thing. They're focusing on not what's going to protect us from the virus, they're focusing on something that's essentially a negligible risk.

EMANUEL GOLDMAN: Now I don't want to dismiss or minimize the impact of this virus, this very serious virus. And what we need to do is the right things to protect ourselves. And that's wearing masks, that's doing social distancing and moving activities outdoors as much as possible. Because we also have evidence now that the sunlight kills the virus, that the warm weather — virus doesn't do very well in the warm weather, that the airflow that you get outdoors is going to be protective. So these are the things that need to be focused on. If you drive yourself crazy focusing on fomites, maybe you won't be as careful when it comes to wearing a mask.

PETER NORD: Yeah, so it's all about that airborne transmission versus the fomite transmission, for sure.

EMANUEL GOLDMAN: Right. Now one other point that I also want to make is I'm not saying that the experiments that were done, were wrong. I'm not disputing the findings of the experiments. They were peer-reviewed experiments, I have no reason to doubt the results that they got. So it's not that the experiments were wrong, but they were the wrong experiments. They were not experiments that bore a relationship to real life.

PETER NORD: Well, there's certainly a significant cost to cleaning, to shutting down the subways. Huge costs. Think what the airlines are going through right now in terms of their service cleanings as well.

EMANUEL GOLDMAN: Right. Right. It's the wrong focus. In fact, at the very beginning of this, the CDC of the United States did not recommend masks, and did talk about the cleaning of fomites. Exactly opposite of the way it should have been. I didn't believe them in the beginning. I started wearing masks right at the start of this. And because of my mother in law, I was wearing gloves as well. But after I did my literature research, I stopped with the gloves.

EMANUEL GOLDMAN: By the way, in hospitals, you still want to wash, you still want to disinfect, you still want to wash surfaces, because you've got a higher concentration of virus there. So you don't want to abandon your caution, you want to you want to err on the side of caution in hospitals.

PETER NORD: Perfect.

EMANUEL GOLDMAN: I don't want to leave the impression that one should stop washing hands. But this is something that you should do anyway, even if there were no pandemic. We wash hands before we prepare food. We wash hands when we go to the bathroom. Our mothers taught us this. Mother knows best. We do want to keep hygiene up, but we just don't need to do it to excess and counterproductive levels.

PETER NORD: Absolutely. So we want to thank you for your time today And we look forward to keeping in touch on this topic as we learn more over the next number of months.

EMANUEL GOLDMAN: Okay. Thank you.

CHRIS SHULGAN: That’s a wrap for this episode of Eat Move Think. We’ll post links and highlights on the website at eatmovethinkpodcast.com, including that letter we mentioned in the opening. Eat Move Think is produced by Ghost Bureau. Senior producer is Russell Gragg. Remember to rate and subscribe to Eat Move Think on your favourite podcast platform. Follow Shaun on Twitter and Instagram @ShaunCFrancis — that's Shaun with a U — and Medcan @medcanlivewell. We'll be back soon with a new episode examining the latest in health and wellness.

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Christopher Shulgan
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