Birth defects most strongly linked to Zika virus infection during pregnancy have increased in parts of the United States that have had local Zika virus transmission, according to a report in CDC’s Morbidity and Mortality Weekly Report (MMWR). Areas with local transmission of Zika – southern Florida, a portion of south Texas, and Puerto Rico – saw a 21 percent increase in births with outcomes most strongly linked to Zika virus in the last half of 2016 compared with births in the first half of that year.
It is not known if this increase is due to local transmission of Zika virus alone, or if there are other contributing factors. Most of the mothers who had babies with the Zika virus-linked birth defects did not have laboratory evidence of Zika virus infection—either because they were not tested, were not tested at the right time, or were not exposed to Zika virus. All cases with birth defects potentially related to Zika virus infection are monitored by birth defects surveillance systems.
“Babies with Zika-related birth defects need all the help they can get, as soon as possible and for as long as they need it,” said CDC Director Brenda Fitzgerald, M.D. “This report highlights the critical importance of documenting birth defects possibly related to Zika and our need to maintain vigilance.”
CDC looked at nearly 1 million births in 2016 in 15 U.S. states and territories, including Florida (select southern counties), Georgia (select metro-Atlanta counties), Hawaii, Iowa, Illinois, Massachusetts, New Jersey, New York (excluding New York City), North Carolina (select regions), Puerto Rico, Rhode Island, South Carolina, Texas (select regions), Utah, and Vermont.
About three out of every 1,000 babies born in 15 states and territories in 2016 had a birth defect possibly associated with Zika virus infection in the mother:
- About half (49 percent) were born with brain abnormalities and/or microcephaly (small head size)
- 2 in 10 (20 percent) had neural tube defects and other early brain abnormalities
- 1 in 10 (9 percent) had eye abnormalities without brain abnormalities
- More than 2 in 10 (22 percent) had nervous system damage, including joint problems and deafness, without brain or eye abnormalities
Because many pregnant women exposed to Zika virus in late 2016 gave birth in 2017, CDC researchers anticipate that there could be another increase in possible Zika-related birth defects when 2017 data are analyzed.
CDC uses tracking systems to find birth defects that might be related to Zika virus:
- U.S. Zika Pregnancy and Infant Registry tracks pregnancies with laboratory evidence of Zika virus infection.
- Zika Birth Defects Surveillance system tracks birth defects possibly related to Zika virus infection, regardless of exposure or laboratory testing.
“Our pregnancy and birth defects surveillance networks are a collaborative effort with state, local, and territorial health departments and are essential to protect mothers and babies affected by Zika virus,” said Peggy Honein, Ph.D., M.P.H., acting director, Division of Congenital and Developmental Disorders, National Center on Birth Defects and Developmental Disabilities. “These networks can also be used as models to help track other known and emerging health threats for mothers and babies.”
For more information about Zika virus and pregnancy visit www.cdc.gov/pregnancy/zika.