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The count of pregnant women in US states and territories who have contracted Zika has sharply risen, thanks to a revised method for counting such infections, the Centers for Disease Control and Prevention said Friday.

As of May 12, 279 pregnant women in the United States had lab evidence of Zika infection. Prior data indicated 113 pregnant women had Zika, but this number didn’t include those without symptoms.

Previously, the CDC only reported the number of cases in pregnant women who had a positive laboratory test result and experienced symptoms or pregnancy complications.


“We think it’s important to cast a wide net,” said Dr. Denise Jamieson, who coleads the pregnancy and birth defects task force in the CDC’s Zika response.

Margaret Honein, another task force cochair, said that the CDC is changing its reporting methods, in part, because of recent reports of women with Zika virus, who do not recall experiencing symptoms, giving birth to babies with microcephaly.


The CDC has been monitoring these women for months and started reporting the total number of women today. Honein, said that the CDC was hoping to start sharing this data a couple of weeks ago, but that it took extra time to make sure the numbers were accurate.

As of May 12, the latest date for which nationwide data is available, the CDC reported that 157 pregnant women in US states and 122 in territories are being monitored for possible Zika virus infection.

The Puerto Rican Health Department also released its own numbers on Friday, reporting that as of May 19 the territory had a total of 139 pregnant women with Zika infections.

Honein said that the majority of pregnancies being tracked are still ongoing, and that less than a dozen adverse effects have been reported so far.

CDC officials said that these numbers are not comparable to the previous reports of the number of women who have Zika virus disease.

The women are tracked through two databases, one for Puerto Rico and one for all other US states and territories. Updated numbers will be released every Thursday at noon, reflecting the count as of a week prior.