New estimate shows frequency of Zika-associated birth defects in US
According to a new estimate published in MMWR, around 5% of U.S. infants born to mothers with a confirmed or possible Zika virus infection during pregnancy had a Zika-associated brain or eye defect, and many had more than one.
The estimate is based on data from nearly 6,800 births that occurred in the U.S. and its territories from December 2015 through March 2018 and were reported to the U.S. Zika Pregnancy and Infant Registry (USZPIR).
The 2015-2016 Zika virus epidemic was centered on Brazil, but widespread local transmission also occurred in Puerto Rico and the U.S. Virgin Islands. On the U.S. mainland, Florida and Texas both reported local transmission.
According to the CDC, there has not been a locally acquired case of Zika virus in a U.S. state since 2017, although they continue to occur in U.S. territories. Zika is spread mainly through the bite of infected Aedes species mosquitoes.
The new MMWR report is the first to describe Zika-associated birth defects from the USZPIR “with data combined from the U.S. states, D.C., and U.S. territories and freely associated states,” the authors said. It describes not only the frequency of birth defects overall but also the most commonly reported defects.
Among the 6,799 births reported to the USZPIR during the study period, 4.6% of infants born to women with confirmed or possible Zika virus infection during pregnancy had a Zika-associated brain or eye defect. The frequency was higher — 6.1% — in a subgroup of pregnancies in which the mother’s infection was confirmed by nucleic acid amplification testing.
Around 35% of infants with a birth defect — 110 out of 315 — had more than one defect. Several brain and eye defects occurred more frequently, including microcephaly, corpus callosum abnormalities, intracranial calcification, abnormal cortical gyral patterns, ventriculomegaly, cerebral or cortical atrophy, chorioretinal abnormalities and optic nerve abnormalities, the researchers reported.
“These findings can help target surveillance efforts to the most common brain and eye defects associated with Zika virus infection during pregnancy should a Zika virus outbreak reemerge, and might provide a signal to the reemergence of Zika virus, particularly in geographic regions without ongoing comprehensive Zika virus surveillance,” the authors wrote.
CDC. Zika cases in the United States. https://www.cdc.gov/zika/reporting/index.html. Accessed Jan. 21, 2022.