STEVE INSKEEP, HOST:
Now let's track the work of disease detectives from the U.S. Centers for Disease Control and Prevention. They've arrived in Brazil to investigate the Zika outbreak that has set off a global health emergency. NPR's Rob Stein is with them. And, Rob, where are you exactly in Brazil?
ROB STEIN, BYLINE: Yes, good morning, Steve. I'm in a city called Joao Pessoa. It's in the northeast corner of Brazil, and this is a part of Brazil that's been hit really hard by Zika. It's really part of the epicenter of the outbreak. And as it happens, I just wanted to sort of mention, that this time of year this is the first place the sun rises anywhere on the continent. So in that way it's kind of an appropriate place for the CDC to be trying to shine a light on this baffling medical mystery.
INSKEEP: What is the question on their minds?
STEIN: So they're really trying to examine this crucial question, which is, is the Zika virus - you know, this virus that everybody thought was very much obscure and everybody thought was pretty harmless until recently - really causing this terrible birth defect, this microcephaly, which causes women to give birth to babies with abnormally small heads and severely damaged brains? And they've come here because so many pregnant women have gotten infected with the virus so that gives them really the best shot at getting to the bottom of what's going on.
INSKEEP: Although this is in a way disturbing, Rob Stein, because we have had so many new stories about the Zika virus causing these problems, what evidence is there to actually prove that it's true?
STEIN: Yeah, I know. I mean, health authorities have been saying at this point that the Zika virus is what they're saying guilty until proven innocent, and that's because the evidence has been mounting that there is a link between Zika and microcephaly. And the reason for that is, you know, in Brazil for example, it looks like there was this big spike in this - what had been a rare birth defect that began right after Zika arrived and started spreading like crazy, but that's really just circumstantial evidence. So they've been trying to strengthen the case and strengthen this link, and they have found other evidence. They've found the virus in the brains of a few babies with microcephaly who died shortly after birth. That makes the case stronger but it still doesn't prove it. And so the CDC's trying to make the case as airtight as possible.
INSKEEP: What puts it beyond a reasonable doubt - to use that term from law?
STEIN: Yeah so what the CDC's doing here is they sent 16 epidemiologists, and they're teaming up with their Brazilian counterparts to form eight teams to do what's known as a case control study. And this is really hardcore, shoe-leather disease detective work. They're literally going to fan out in the region and go door-to-door to try to track down at least a hundred women who have had babies with microcephaly since the Zika outbreak began. Once they find them they'll gather as much information about them as they can. They'll, you know, take blood samples from the mothers and from the babies to test for signs of the Zika infection. And they'll ask the mothers lots and lots of questions. Did the moms have symptoms of Zika when they were pregnant? If they did, when exactly in the pregnancy? And - this is the key thing - they're also going to try to find out if there's anything else that may explain what was going on that's not Zika. Did they have, you know, any other infections that are known to cause microcephaly or maybe infections that, combined with Zika, may be the cause? Or were they exposed to something in the environment, some sort of toxin that may be to blame? They'll do the same thing with hundreds of other very similar women who had healthy babies about the same time and compare them to see if they can make this link stronger or debunk it if it's not true.
INSKEEP: When you said shoe leather, you meant it. Rob, thanks very much.
STEIN: Oh, sure, nice to be here.
INSKEEP: That's NPR Health Correspondent Rob Stein in northeastern Brazil, where scientists are trying to prove beyond a doubt that the Zika virus is responsible for birth defects.
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