More birth defects reported in states with Zika cases

MIAMI — The kinds of birth defects associated with Zika, including microcephaly and other brain abnormalities, have increased in parts of the United States where mosquitoes were spreading the virus in 2016, including South Florida, according to a new report from the federal Centers for Disease Control and Prevention.

Areas with local spread of Zika — including Florida, a portion of southern Texas, and Puerto Rico — saw a 21 percent spike in these kinds of birth defects during the second half of 2016 compared with births that took place during the first half of that year, CDC officials reported.

But researchers said they do not know if the increase is due to local spread of Zika or other factors because most mothers who delivered babies with birth defects associated with the virus did not have laboratory evidence of infection. Those mothers either were never tested, were not tested at the right time, or were not exposed to Zika, CDC officials said.

Researchers analyzed nearly 1 million births from 2016 in 15 states and territories as part of the report, which provided the first comprehensive data on the prevalence of birth defects potentially linked to Zika.

They identified 2,962 babies and fetuses with birth defects potentially related to Zika, including 1,456 with brain abnormalities or microcephaly — which causes abnormally small heads and incomplete brain development. There was no state breakdown.

An additional 581 had neural tube defects, 262 had eye abnormalities and 662 had some other form of central nervous system dysfunction.

Among the nearly 3,000 birth defects identified, though, a total of 2,821 cases either never received Zika testing or their results were not available for the report.

Because the increase in birth defects was detected during the second half of 2016, CDC researchers said more surveillance is necessary to capture births from 2017, when many pregnant mothers affected by Zika would have delivered their babies.