ARI SHAPIRO, HOST:
Nearly 300 pregnant women in the U.S. and its territories have tested positive for a Zika virus infection. It sounds like a big jump in cases, but it's mostly because of a change in how the numbers are reported by the Centers for Disease Control and Prevention. NPR's Nell Greenfieldboyce explains.
NELL GREENFIELDBOYCE, BYLINE: It used to be that a pregnant woman would have to have more than just lab test results to get reported in the official CDC numbers. She'd also have to have symptoms of Zika, like rash or fever. But that's no longer the case. Margaret Honein is chief of the CDC's Birth Defects branch. She says the agency will now include all pregnant women with positive test results, even if they don't recall any symptoms. That's because there's growing evidence that an infected woman doesn't need feel sick for her pregnancy to be at risk.
MARGARET HONEIN: As the data accumulated about the risk of asymptomatic infections, it seemed more and more important to be very transparent and share publicly the full number of pregnant women at risk of adverse outcomes associated with Zika.
GREENFIELDBOYCE: She says so far, officials know of fewer than a dozen bad outcomes, like miscarriage or birth defects.
HONEIN: But we don't have full information yet on all of the outcomes.
GREENFIELDBOYCE: ...Because most of the pregnancies are ongoing. The CDC says it has no evidence that mosquitoes are spreading Zika in the continental United States. Here, the 157 pregnant women with Zika either had traveled to an affected region or had sex with a traveler.
Today top health officials briefed President Obama on the Zika situation. He spoke to reporters in the Oval Office and said work was underway on a vaccine and better diagnostics.
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BARACK OBAMA: We're also working with all the states so that they are properly prepared if we start seeing an outbreak here in the continental United States during the summer when, obviously, mosquitoes are more active.
GREENFIELDBOYCE: He said all that work costs money and urged Congress to fully fund his $1.9 billion request for Zika. Nell Greenfieldboyce, NPR News.
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