Population-based Surveillance of Birth Defects Potentially Related to Zika Virus Infection — 15 States and U.S. Territories, 2016

Augustina Delaney, PhD; Cara Mai, DrPH; Ashley Smoots, MPH; Janet Cragan, MD; Sascha Ellington, MSPH; Peter Langlois, PhD; Rebecca Breidenbach, MPA; Jane Fornoff, PhD; Julie Dunn, PhD; Mahsa Yazdy, PhD; Nancy Scotto-Rosato, PhD; Joseph Sweatlock, PhD; Deborah Fox, MPH; Jessica Palacios, MPH; Nina Forestieri, MPH; Vinita Leedom, MPH; Mary Smiley, MS; Amy Nance, MPH; Heather Lake-Burger, MPH; Paul Romitti, PhD; Carrie Fall, MS; Miguel Valencia Prado, MD; Jerusha Barton, MPH; J. Michael Bryan, PhD; William Arias, MPH; Samara Viner Brown, MS; Jonathan Kimura, MPH; Sylvia Mann, MS; Brennan Martin, MPH; Lucia Orantes, PhD; Amber Taylor, MPH; John Nahabedian, MS; Amanda Akosa, MPH; Ziwei Song, MPH; Stacey Martin, MSc; Roshan Ramlal, PhD; Carrie Shapiro-Mendoza, PhD; Jennifer Isenburg, MPH; Cynthia A. Moore, MD, PhD; Suzanne Gilboa, PhD; Margaret A. Honein, PhD


Morbidity and Mortality Weekly Report. 2018;67(3):91-96. 

In This Article


Leveraging existing birth defects surveillance systems permitted rapid implementation of surveillance for birth defects potentially related to Zika virus infection early during the U.S. Zika virus outbreak. The prevalence of birth defects strongly linked to Zika virus infection increased significantly in areas with local Zika virus transmission (29 more than were expected in the second half of 2016 compared with observed prevalence in the first half). This finding underscores the importance of surveillance for birth defects potentially related to Zika virus infection and the need for continued monitoring in areas at risk for Zika transmission and exposure.

An increase in birth defects potentially related to Zika was only observed in jurisdictions with local Zika virus transmission, and this difference was significant when NTDs were excluded. Brain and eye abnormalities and consequences of CNS dysfunction have been most consistently described in cases of congenital Zika infection, whereas the evidence supporting a possible association between NTDs and Zika virus infection during pregnancy is weak.[1,2] In jurisdictions with "lower" (low or no travel-associated) Zika prevalence, the reason for the significant decrease in prevalence of birth defects potentially related to Zika (both including NTDs and excluding NTDs) is not clear. However, birth defects surveillance data typically are not final until approximately 24 months after the end of the birth year, and this release of data only 12 months after the end of the birth year likely resulted in less complete ascertainment of birth defects in late 2016 compared with early 2016. Further case ascertainment from the final quarter of 2016 is anticipated in all jurisdictions. In addition, the peak occurrence of birth defects potentially related to Zika virus infection is expected to have occurred in the 2017 birth cohort because the peak of Zika virus transmission occurred in Puerto Rico in August 2016, and local transmission of Zika virus was identified in southern Florida in June 2016 and in southern Texas in November 2016.[4–7]

The overall prevalence of the birth defects in this analysis (3.0 per 1,000 live births) was similar to a previously published baseline prevalence of birth defects potentially related to Zika virus infection from 2013–14 (2.9 per 1,000 live births; 95% CI = 2.7–3.1).[8] The findings presented here included data from an additional 12 jurisdictions, which covers a larger birth cohort totaling nearly 1 million live births, representing approximately one fourth of the total live births in the U.S. states and territories.

The findings in this report are subject to at least three limitations. First, the three jurisdictions with local Zika virus transmission differed from one another in the scope and timing of identified local transmission of Zika virus. Whereas Puerto Rico experienced a widespread outbreak that began in early 2016, local transmission in Texas was not confirmed until November 2016. In addition, jurisdictions with local transmission also had a high prevalence of travel-related Zika virus disease in 2016,[3] which could have contributed to the observed increased prevalence in birth defects. Second, increased awareness of birth defects potentially related to Zika virus infection in areas with local transmission might have resulted in increased efforts focused on rapid and complete identification of these birth defects cases during the second half of 2016. However, a significant increase in NTD prevalence was not observed. Although more complete ascertainment might partially explain the increased prevalence observed in areas with local transmission, it is unlikely that it would lead to a significant change, given the longstanding, mature surveillance systems, the standardized case review process, and no observable change in the prevalence of NTDs. Finally, jurisdictions in this analysis might differ in population demographics and systematic case-finding methodology, contributing to differences in observed prevalences among the three groups.[9] A comparison of the prevalences in the first and second halves of the year was used to partially control for regional differences and monitor trends for those specific jurisdictional groups rather than to compare one group with another.

Collaboration between state and territorial Zika pregnancy and infant registries and birth defects surveillance systems provides a model for using the complementary approach of a prospective, exposure-based surveillance and conventional disease-based surveillance to respond to an emerging public health threat. The U.S. Zika Pregnancy and Infant Registry¶¶ can provide an early alert mechanism regarding clinical characteristics and manifestations of infants and fetuses with potential congenital infection; over 7,000 pregnancies with laboratory evidence of Zika virus infection have been reported, and CDC is monitoring pregnancy and infant adverse outcomes (https://www.cdc.gov/pregnancy/zika/data/pregnancy-outcomes.html). Established birth defects surveillance systems can adapt to monitor other emerging pregnancy, infant, and newborn outcomes of concern beyond structural birth defects, including functional problems such as hearing loss, and can provide additional clinical information through standardized data collection and clinical review. Finally, birth defects surveillance systems can provide an important mechanism for facilitating timely access to services among infants with birth defects and serve as a resource for assessing subsequent health and developmental outcomes among these children. The unique contributions of ongoing birth defects surveillance and the U.S. Zika Pregnancy and Infant Registry are both critical to optimally monitoring pregnant women and infants from the threat of Zika virus infection and implementing appropriate prevention efforts.[10]

¶¶The U.S. Zika Pregnancy and Infant Registry includes the U.S. Zika Pregnancy Registry and the Zika Active Pregnancy Surveillance System, which together collect information about pregnancy and infant outcomes among women with laboratory evidence of Zika virus infection during pregnancy in the 50 states, the District of Columbia, and U.S. territories, until at least 2 years of age. (https://www.cdc.gov/pregnancy/zika/research/registry.html).