Possible Zika Virus Infection Among Pregnant Women — United States and Territories, May 2016

Regina M. Simeone, MPH; Carrie K. Shapiro-Mendoza, PhD; Dana Meaney-Delman, MD; Emily E. Petersen, MD; Romeo R. Galang, MD; Titilope Oduyebo, MD; Brenda Rivera-Garcia, DVM; Miguel Valencia-Prado, MD; Kimberly B. Newsome, MPH; Janice Pérez-Padilla, MPH; Tonya R. Williams, PhD; Matthew Biggerstaff, MPH; Denise J. Jamieson, MD; Margaret A. Honein, PhD; Zika and Pregnancy Working Group


Morbidity and Mortality Weekly Report. 2016;65 

In This Article


Through the establishment of these pregnancy surveillance systems, CDC, in collaboration with state, local, tribal, and territorial partners, is reporting and actively monitoring pregnant women with laboratory evidence of possible Zika virus infection. These surveillance systems monitor pregnant women at risk for adverse congenital outcomes attributable to possible Zika virus infection. Including pregnant women with laboratory evidence of possible Zika virus infection but without a reported history of symptoms more than doubles the number of pregnancies being monitored, compared with pregnancies meeting the interim CSTE case definition and reported by ArboNET.

Limiting surveillance to symptomatic women with confirmed or probable Zika virus disease or to women already affected by an adverse pregnancy outcome excludes a substantial proportion of women with asymptomatic and possible Zika virus infection during pregnancy. In contrast, the broader case definition used for the USZPR and ZAPSS surveillance systems might overestimate Zika virus infection among women screened for infection because of crossreactivity with dengue and other flaviviruses, particularly among residents of U.S. territories and travelers with a history of prior flavivirus infection or flavivirus vaccination,[8] or nonspecific reactivity.

Case reports indicate that fetuses and infants of pregnant women with asymptomatic Zika virus infection might be at risk for microcephaly and other severe brain defects.[9,10] Following pregnant women with laboratory evidence of possible Zika virus infection in the surveillance system, regardless of symptoms, allows better characterization of the full impact and consequences of infection to the mother and her offspring, and might allow for better stratification of risk for adverse congenital outcomes.[1] An important role of the USZPR and ZAPSS surveillance systems is evaluating the range of outcomes associated with Zika virus infection during pregnancy. Pregnancy outcomes are currently being monitored and will be shared in future reports. It is critical that health care providers inform state, local, tribal, and territorial health departments of any pregnant women with laboratory evidence of possible Zika virus infection under their care.

The findings in this report are subject to at least three limitations. First, data provided to the jurisdictions and CDC regarding symptoms and symptom onset might not be accurate or complete because of variability in recall by patients or data available to jurisdictions. Second, only pregnant women who are tested for Zika virus infection are included, thereby potentially underestimating the prevalence of infection and outcomes among all pregnant women. Finally, all states are not included in the USZPR, possibly affecting the representativeness of these data with regard to all pregnant women identified with a possible Zika virus infection.

One challenge of this Zika virus outbreak is the lack of understanding of the magnitude of risk and spectrum of outcomes associated with Zika virus infection during pregnancy. The USZPR and ZAPSS are surveillance systems established to enumerate and describe pregnancies with Zika virus infection and risk for adverse outcomes associated with infection during pregnancy. Findings from these U.S. surveillance systems are expected to improve understanding of Zika virus infection during pregnancy, enhance risk assessment and counseling of pregnant women and families, advance clinical care, and assist states and territories to anticipate and plan needed resources and increase prevention efforts.¶¶