EXECUTIVE SUMMARY

A new CDC report shows that among pregnant women in the United States with completed pregnancies and laboratory evidence of possible recent Zika infection, 6% overall delivered a fetus or infant with evidence of a Zika-related birth defect, and among women with first-trimester Zika infection, 11% delivered a fetus or infant with a birth defect.

  • The report highlights the importance of CDC guidance to test all pregnant women with possible exposure to Zika virus regardless of whether they exhibited symptoms of Zika, and to test infants born to mothers with possible Zika virus infection.
  • The CDC continues recommending that pregnant women not travel to areas with Zika. If a pregnant woman travels to or lives in an area with active Zika virus transmission, she should discuss such travel with her healthcare provider and strictly follow steps to prevent mosquito bites and sexual transmission of Zika virus, including use of abstinence or condoms.

A new CDC report shows that among pregnant women in the United States with completed pregnancies and laboratory evidence of possible recent Zika infection, 6% overall delivered a fetus or infant with evidence of a Zika-related birth defect, and among women with first-trimester Zika infection, 11% delivered a fetus or infant with a birth defect.1

The report combined data from the continental United States and Hawaii that were collected in collaboration between CDC and state and local health departments to monitor pregnancies with laboratory evidence of Zika virus infection. As of Sept. 22, 2016, 442 women with possible Zika virus infection in the U.S. Zika Pregnancy Registry had completed their pregnancies. Twenty-six of the completed pregnancies (6%) were reported to demonstrate one or more of the birth defects potentially related to Zika virus infection during pregnancy. Among women infected with Zika in the first trimester of pregnancy, 11% were reported to deliver fetuses or infants with birth defects.1

Research indicates that the proportion of pregnancies with birth defects was similar for pregnant women who did or did not experience symptoms, about 6% in each group. The 18 infants with a finding of microcephaly represent 4% of the completed pregnancies. Researchers note this prevalence is substantially higher than the background prevalence of microcephaly in the United States of about seven per 10,000 live births, or about 0.07% of live births.

Scientists note that the 26 birth defects occurred among fetuses/infants of pregnant women who were exposed to Zika virus during their pregnancies in the following locations with active Zika virus transmission: Barbados, Belize, Brazil, Colombia, Dominican Republic, El Salvador, Guatemala, Haiti, Honduras, Mexico, Republic of Marshall Islands, and Venezuela.

This study indicates that the rate of microcephaly and other fetal malformations related to Zika is similar among babies born in the United States — whose mothers were infected during travel to a dozen countries with active Zika transmission — to the estimated rate in Brazil, observes CDC Director Tom Frieden, MD, MPH.

“Zika poses a real risk throughout pregnancy, but especially in the first trimester; it’s critical that pregnant women not travel to areas where Zika is spreading,” Frieden said in an announcement accompanying the data publication.

The report highlights the importance of CDC guidance to test all pregnant women (http://bit.ly/2bRQag6) with possible exposure to Zika virus regardless of whether they exhibited symptoms of Zika, and to test infants (http://bit.ly/2j8aBrQ) born to mothers with possible Zika virus infection.

Follow CDC Recommendations

The CDC continues to recommend that pregnant women not travel to areas with reported Zika outbreaks. If a pregnant woman travels to or lives in an area with active Zika virus transmission, she should discuss such travel with her healthcare provider and strictly follow steps to prevent mosquito bites and sexual transmission of Zika virus, including use of abstinence or condoms. (For more information to offer patients, please visit: http://bit.ly/1shEBFh.)

The CDC also continues encouraging women considering pregnancy and their partners in areas with active Zika transmission to talk to their healthcare providers about pregnancy planning so they know the risks and the ways to reduce them. (For more information, please visit: http://bit.ly/2g4t2Ml.)

Many of the short- and long-term effects of prenatal Zika infection on a baby are unknown. Until more is known, CDC advises following the Interim Guidance for the Clinical Evaluation and Management of Infants with Congenital Zika Virus Infection — United States, August 2016, for any baby diagnosed with congenital Zika virus infection.

Winter Doesn’t Deter Mosquito Activity

As temperatures fall this winter, public officials advise not to let guards down when it comes to mosquitoes that can carry the Zika virus. According to James Diaz, MD, DrPH, professor and program director of environmental/occupational health sciences at Louisiana State University Health New Orleans School of Public Health, not only can the eggs of Aedes species mosquitoes survive winter, wide variations in daytime temperatures can stimulate egg-laying and shorten the time it takes for mosquitoes to become infective after biting a person with Zika.

“What’s more, researchers have shown that while relatively rare, Aedes aegypti mosquitoes are able to transmit Zika to their offspring, a mechanism allowing the virus to survive from one season to the next,” Diaz said in a press statement accompanying the publication of his paper detailing the characteristics of the mosquitoes capable of transmitting the Zika virus in the United States.2

Aedes species eggs can survive in conditions that adult mosquitoes cannot, the paper notes. Even when their source of water has evaporated, these mosquito eggs can survive desiccation, remaining environmentally stable and viable up to a year — all it takes is a little rain for them to hatch, the paper states.2

“As we learn more about the consequences of Zika infection, including the recent revelation that babies of Zika-infected mothers who had normal head sizes at birth have been diagnosed with microcephaly months later, it is vital that we know this enemy and remain vigilant in protecting ourselves,” Diaz concludes.

REFERENCES

  1. Honein MA, Dawson AL, Petersen EE, et al; US Zika Pregnancy Registry Collaboration. Birth defects among fetuses and infants of US women with evidence of possible Zika virus infection during pregnancy. JAMA 2017;317:59-68.
  2. Diaz JH. Preparing the United States for Zika virus: Pre-emptive vector control and personal protection. Wilderness Environ Med 2016;27:450-457.