Super Spreaders: Dr. Sanjay Gupta's coronavirus podcast for June 18

(CNN)Some people are responsible for spreading the virus more than others. These people have been called "super spreaders," but are they really different from the rest of us? CNN Chief Medical Correspondent Dr. Sanjay Gupta talks to Elizabeth McGraw, the director of the Center for Infectious Disease Dynamics and professor of entomology at Penn State University, about who or what a super spreader is.

You can listen on your favorite podcast app or read the transcript below.
Dr. Sanjay Gupta: You've probably been hearing the term "super spreader" a lot these days.
In March, a single member of a choir in Washington state infected 52 other people during a two and a half hour practice session. In South Korea, more than a hundred new infections were linked to a 29-year-old man who tested positive after visiting several nightclubs and bars in a single night.
    So who, or maybe what, is a super spreader? Why is it so dangerous? And perhaps most importantly — who among us are potential super spreaders?
    I'm Dr. Sanjay Gupta, CNN's chief medical correspondent. And this is "Coronavirus: Fact vs. Fiction."
    Elizabeth McGraw, director of the Center for Infectious Disease Dynamics and professor of entomology at Penn State University: Yeah, so the word "super spreader," it's a bit messy. I mean, we sort of, for most diseases, have a sense for how many people a single individual is likely to infect. So if someone walked into a room with a bunch of people who were equally susceptible, we ask the question, how many are they likely to infect?
    Gupta: That's Professor Elizabeth McGraw, the director of the Center for Infectious Disease Dynamics at Penn State. I called her recently because I wanted to learn more about super spreader events.
    Now before you understand them, you have to first understand how scientists even measure how infectious a disease really is. They do that by starting with a number called the "R-naught" or "R0."
    McGraw: R0 is the number that we use to measure how many individuals you're likely to infect. So for coronavirus, we think that sits around two point five. And so when we say that average is two point five, what we really mean is that most people are probably only infecting, you know, less than two point five.
    But then there are a number of people in the population who are dragging that average up by infecting large numbers of people. There's not a hard-and-fast rule for when someone becomes a super spreader. So some of the recent studies have used the number of, you know, infecting six to eight individuals as sort of the range, anything above six or eight as meeting the requirements for a super spreading event.
    Gupta: Should we be saying that the individual is a super spreader or is it the event is a super spreading event?
    McGraw: I think it's more the event. And, you know, if we want to be really effective and try and stop super spreading, and we know if we could stop super spreading, we'd have a really big impact on this pandemic. We can't really determine who might be a super spreader or, you know, we really don't have the knowledge or the resources or the ability to study or understand that. But we do know the environments where they can happen.
    And so anytime someone who is positive with the virus puts themselves in a situation where they could infect a large number of people, then you can have a super spreading event regardless of what their underlying biology might be.
    Gupta: So anybody could potentially be a super spreader, depending on the circumstances?
    McGraw: Exactly. And so I think that's important for everyone to remember that all of us could be super spreaders.
    Gupta: If I had the virus and I was within 6 feet of somebody, is there a way to contextualize, how likely is it that I would then spread that virus to the other person?
    McGraw: Well, I think that's a complicated answer. I don't think I can give you a number. I think I can tell you that distance matters. You should remember that 6 feet thing is not perfect. So if you're not wearing a mask and you're coughing, and someone's 7 feet away from you, they might also catch it. And also exposure time matters.
    Gupta: What makes coronavirus spread so well? What is it about this virus?
    McGraw: One thing is that we think that the human population is entirely naive, meaning that they have no immune protection. So that just means the susceptibility is high in humans. Whereas with flu, you know, all of us have some level of protection, be it from past history of infection or from getting the flu shot, which everyone should get.
    And then, and I think this is the most powerful thing, is that it can spread in this asymptomatic or pre-symptomatic stage. And in fact, as you pointed out, that is when humans are most contagious. And so it's very effective at transmitting and getting onto that next host before we're even aware, which makes it very hard to change your behavior after the fact. In some ways, it's too late.
    Sometimes when people have, by the time they found out they're positive, and if they haven't been isolating during that period prior to finding out they're positive, they've probably already infected several people.
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