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How Public Health Officials Use 'Contact Tracing' To Track An Epidemic's Spread


The coronavirus has governments and health experts worldwide scrambling for a way to stop it from spreading, and one of the oldest methods of containing a pandemic is still one of the most widely used methods today. It's called contact tracing, and it's as simple as it sounds. You find out who an infected person has been in contact with, you test those people, and you quarantine them if they are infected. But how effective is contact tracing with something like the coronavirus? Well, for that, we turn now to Ranu Dhillon. He's a doctor at Brigham and Women's Hospital in Boston, and he was an adviser to the national Ebola coordinator in Guinea.


RANU DHILLON: Thank you for having me.

CHANG: So I understand that you have overseen the use of contact tracing in West Africa for years now. Can you just walk us through what contact tracing actually looks like?

DHILLON: Yeah. So on the ground, the way contact tracing plays out is once you identify somebody who has been infected with the disease in question, you then try to - through interviewing that person and canvassing around their neighborhood, you try to understand all the people who may have been in close confines or otherwise been exposed to that person in the preceding days and weeks. The premise is that the next batch of infections is likely to arise among those people who that person may have exposed.

Once you've identified those people, you then want to be able to follow them during that period of time during which they may become infected and develop symptoms. Therefore, if they start becoming sick, you can immediately test them, and if they do test positive, you can immediately start treatment for them. And then the second part that's critical is you can isolate them so that they're not in a position where they can expose others.

CHANG: You know, I'm just sort of thinking about all the people I come in contact with in just one day. I don't know if I would remember everybody.

DHILLON: Yeah, and that's exactly one of the critical challenges with contact tracing, especially now that we're living in a more urbanized world...

CHANG: Right.

DHILLON: ...A world where people are traveling frequently on buses, trains. In any place in the world now, even in some of the most remote and poor areas, you have high mobility of populations.

CHANG: OK, so if there are challenges inherent in an urban environment when it comes to contact tracing - I mean, we are talking about Wuhan, which is a city of at least 11 million people. What other methods could you rely on in a city like that?

DHILLON: What you can do is take any patients who are presenting with symptoms that could be indicative of the disease at hand and have them be isolated until they can get tested by laboratory means. Now, the tricky thing about doing that in a place like Wuhan right now is going to be that there may be so many patients coming forward with those symptoms, and you can't realistically isolate all of them in a hospital in a week. Testing for that could take hours at least, if not days. What you can do, though, is when somebody does present and they're not so sick, you can take a sample for testing, have that person return home with precautions of how to not expose other people in their home. And when the results come back, follow up with them.

CHANG: I'm curious how different viruses compare with each other when it comes to contact tracing. I mean, are there inherent limitations to a method like contact tracing when it comes to the coronavirus versus, say, the Ebola virus?

DHILLON: Definitely. So with Ebola, as terrible as that virus is, one of the things that makes it a little bit easier to track down and manage is that in order to get infected, you typically need to be in really close contact with someone and particularly with their bodily fluids. With this current coronavirus that we're facing, we still don't know where on the spectrum this one falls. And we also don't know how infectious it is in terms of - even if it were airborne or spread through droplets or close contact, even within those different modalities of transmission, you can have some viruses that are very, very contagious and some that are relatively less.

CHANG: Ranu Dhillon was an adviser to the national Ebola coordinator in Guinea. He joined us via Skype.

Thank you very much for joining us today.

DHILLON: Thank you for having me. Transcript provided by NPR, Copyright NPR.