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CDC Identifies Risk of Developing Zika Complications Based on Trimester of Infection

JUN 08, 2017 | SARAH ANWAR
The Centers for Disease Control and Prevention (CDC) just published a Morbidity and Mortality Weekly Report (MMWR) highlighting data on the largest number of completed pregnancies with lab-confirmed Zika virus infection. In addition, during a telebriefing, CDC Acting Director, Anne Schuchat, MD, shared the CDC’s stance on the end of the Zika epidemic in Puerto Rico.
This MMWR report is the first of its kind from US territories, including the Federated States of Micronesia, American Samoa, the Republic of Marshall Islands, the US Virgin Islands, and the Commonwealth of Puerto Rico.
The report reflects data collected between January 1, 2016 and April 25, 2017, and includes data on 2,549 completed pregnancies, 1,508 of which had lab-confirmed Zika virus infection. Of the completed pregnancies, 122 infants (5%) exhibited Zika-related birth defects, with 5% of afflicted infants born to symptomatic mothers and 4% born to asymptomatic mothers. The CDC notes that this number does not constitute a clinical significance in terms of risk of infants born to symptomatic mothers developing complications versus those born to asymptomatic mothers.
Zika lab testing results were reported for only 59% of liveborn infants included in the registry. Of those, 52% received neuroimaging and 79% had hearing tests. The CDC stresses the importance of performing head ultrasounds on infants born to mothers with confirmed Zika infection, as these tests can show abnormalities that aren’t apparent after birth.
The report also highlights that the greatest incidence of Zika-associated birth defects was apparent among infants born to mothers infected during the first trimester: the results showed that 8% of infants born to Zika-infected mothers in US territories developed complications compared with 15% of those born in US states. According to a press release, “these estimates are based on relatively small numbers and are not statistically different.” Infection during the second trimester resulted in the second highest incidence of complications (5%), and infection during the third trimester was found to have the lowest incidence of complications (4%). On average, the CDC estimates that 1% to 13% of Zika infections that occur during the first trimester of pregnancy lead to microcephaly. However, this MMWR report is the first to identify “preliminary estimates of risk for each trimester.”
Another important finding that Peggy Honein, PhD, co-lead on the Pregnancy and Birth Defects Task Force for CDC Zika Response, shared during the telebriefing, is that these findings are consistent with a previous CDC report, published in early April 2017, which noted that, of completed pregnancies with a possible Zika virus infection, 5% may result in Zika-related complications.

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