ARI SHAPIRO, HOST:
To stop the coronavirus from spreading, you need to know how people have been catching it. That's why researchers have been digging into contact tracing data from countries that had early outbreaks. And they've developed a clearer picture of coronavirus transmission - which situations are high risk and which are relatively safe. This could be especially useful as some parts of the U.S. begin opening up. Dr. Muge Cevik is an infectious disease specialist at the University of St. Andrews in Scotland, and she has been studying this research from around the world.
Welcome to ALL THINGS CONSIDERED.
MUGE CEVIK: Thank you so much.
SHAPIRO: When you look at contact tracing and you find out where people got infected and how they caught this disease, what do you learn about which situations are high-risk versus low-risk?
CEVIK: So after examining this series of contact tracing studies from all around the world, we can say that there are some trends. I know people regularly worry about grocery stores, bike rides and runners. But what we can say so far is most of the spread happens in groups of adults and usually indoors. And the majority of risk is, you know, in crowded environments with stagnant air.
SHAPIRO: When you say the majority of risk, are we talking about 40% transmission versus 60% transmission or more like 90% to 10%?
CEVIK: So I guess it's more like the majority of infections are occurring in this environment. Almost 80% of infections are caused by a really small number of patients. So this...
SHAPIRO: Yeah. I was shocked to read this - that, like, 80% of transmissions are caused by 9% percent of infected people. I mean, that's shocking to me. Can you explain that?
CEVIK: So this is mostly about the behavior involved. So if an infected person, when they're the most infectious - what we know so far is it's mostly around the time people just about to have the symptoms or have some minor symptoms go to big events where many people gather together, spend time together. Then many people can be exposed and also infected, you know?
SHAPIRO: A big event like a funeral or a birthday party or a church service.
CEVIK: Exactly. Exactly.
SHAPIRO: As you looked over these studies, what jumped out to you as specific cases of widespread infection and perhaps places where it was not as widespread as the fear and anxiety might have suggested?
CEVIK: So there was a recent study from China where they identified an infected case who's working in the supermarket, and they followed up 8,000 contacts of this person. This included supermarket employees, family members of the confirmed case and supermarket clients. What they found was if you're a supermarket client, your chance of getting infected is 0.02%.
CEVIK: So it's very, very low. But whereas if you are a supermarket employee, because you're exposed multiple times, your risk of getting infected might be 9%. If you're a family member of an infected person, your risk of infection is 12%. So I think we just need to give a range of different risk to people. So outdoors is definitely safer than indoors, nonpeak hours is safer than peak hours, and noncrowded areas safer than very crowded areas.
SHAPIRO: How does this new understanding of what activities are high- versus low-risk change the way we think about basic precautions like hand-washing, mask-wearing, social distancing - things like that?
CEVIK: Yeah. I mean, I guess, like, what I feel is that at the end of the day, we need to learn how to live with this virus on the long run. And if we could provide individuals with this information, people will be more aware of their actions in general. So every activity, every measure to minimize the risk of getting infected counts. So that includes, you know, avoiding crowds...
SHAPIRO: Especially indoors.
CEVIK: ...Especially indoors, but also, you know, hand-washing, continuing with social distancing because we can't completely eliminate the risk. We can minimize the risk. So this is, I think, really crucial.
SHAPIRO: Dr. Muge Cevik is an infectious disease specialist at the University of St. Andrews in Scotland.
Thank you for joining us today.
CEVIK: Thank you. Transcript provided by NPR, Copyright NPR.