How many U.S. pregnancies affected by Zika? Almost 300, CDC says

The Centers of Disease Control and Prevention has tracked close to 300 pregnant women with Zika virus in the U.S. and its territories. These figures come as part of the health agency’s decision to release a weekly update on the numbers of pregnant women dealing with the mosquito-borne disease.

“As of today, national reporting of the number of U.S. pregnant women affected by Zika virus will change,” said Dr. Denise Jamieson, co-leader of the CDC’s pregnancy and birth defects team for the Zika response. These cases will be compiled in a new Zika pregnancy registry that will be updated every Thursday.

The new report more than doubles the number of known Zika-affected pregnancies in the U.S. — from 113 reported on May 11 to 279. The majority of the known cases — 157 — reside in U.S. states, while the remaining 122 live in territories.

Previously, the CDC only released public data on a subset of cases. Those numbers were limited to when a laboratory test confirmed an infection during pregnancy, women who reported symptoms while carrying a child or those who had a history of possible exposure with pregnancy complications consistent with Zika, such as miscarriage or birth defects.

Now, the agency’s public records will also include asymptomatic patients, or those who didn’t show signs of the disease during pregnancy. Up to 80 percent of people who catch the virus do not show symptoms.

“We’ve learned a lot in the past four months, and now we know of reports with asymptomatic Zika infections linked to microcephaly, brain defects and miscarriage,” said Margaret Honein, chief of the CDC’s birth defects branch.

The CDC, as of now, is not releasing data on how many of these pregnancies result in adverse outcomes. Honein said a majority of 279 pregnancies are still ongoing, and in some cases, it may be too soon to tell. Yet when pressed for a ballpark figure, she said less than a dozen of the cases have yielded birth defects or complications like miscarriages.

Honein said the CDC isn’t giving specific details on those adverse outcomes in order to respect the privacy of patients and families.

“Since most of the pregnancies that we are monitoring are ongoing, it’s not possible to use this information to estimate the risk of adverse outcomes,” Honein said. The agency will need to monitor these cases for longer periods of time before researchers can calculate how many end in adverse outcomes.

Moreover, the health agency isn’t stating what percentages of these women caught the virus via sexual transmission. The report states that most of the cases have been associated with travel, but an undefined number involve sexual transmission.

Honein said the pregnancy registry includes statistics tracked by the CDC for all 50 states and territories, except Puerto Rico, which independently compiles its own numbers using their Zika Active Pregnancy Surveillance System (ZAPSS).

“Because of the potential risks of Zika virus during pregnancy, the CDC’s top priority for the Zika response will continue to be protecting pregnant women and their fetuses,” Honein said.

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