Zika-Related Birth Defects 20 Times Higher Than Pre-Zika

Veronica Hackethal, MD

March 03, 2017

The number of children born with birth defects potentially related to Zika virus was 20 times higher in 2016 than before the virus arrived in the United States, providing further proof of the link between Zika and birth defects, according to findings published in the March 3 issue of the Morbidity and Mortality Weekly Report.

"Data on birth defects in the pre-Zika years serve as benchmarks to direct rapid ascertainment and reporting of birth defects potentially related to Zika virus infection," Janet D. Cragan, MD, from the National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia, and colleagues write.

"The higher proportion of these defects among pregnancies with laboratory evidence of possible Zika virus infection supports the relationship between congenital Zika virus infection and birth defects," they add.

Congenital Zika infection has been linked to a range of serious brain and central nervous system malformations. However, these defects are not unique to Zika, and the full range of neurological abnormalities remains unclear.

To better evaluate birth defects potentially related to Zika and how these might have changed since arrival of the virus in the United States, researchers analyzed surveillance data on all types of birth defects from before Zika was introduced in Massachusetts (2013), North Carolina (2013), and Atlanta, Georgia (2013 - 2014).

They identified 747 infants born with one or more defects that met the CDC surveillance case definition for congenital Zika infection.

Most frequently, these children had brain abnormalities or microcephaly (52%; n = 392; prevalence, 1.50 per 1000). Thirty-one percent (n = 229; prevalence, 0.88 per 1000) had neural tube defects and early brain malformations. Eleven percent (n = 81; prevalence, 0.31 per 1000) had eye abnormalities occurring without brain abnormalities. Six percent (n = 45; prevalence, 0.17 per 1000) had other central nervous system dysfunction (joint contractures and congenital deafness) occurring without brain or eye abnormalities.

The researchers then compared the prevalence of these birth defects with data after Zika was introduced, housed in the US Zika Pregnancy Registry (USZPR). The USZPR showed that 442 women with laboratory tests suggesting Zika infection completed pregnancies between January 15 and September 22, 2016.

Among them, 26 infants were born with defects potentially related to Zika, representing a prevalence (58.8 per 1000) that is 20 times higher than before Zika was introduced (2.86 per 1000). The prevalence of children with a brain abnormality or microcephaly (49.8 per 1000) was 33 times higher than during the pre-Zika years (1.5 per 1000).

The authors note several limitations, including the possibility that these results may not generalize to the broader US population. Because the USZPR only has data from women with laboratory tests suggestive of Zika infection, these women may receive closer follow-up than other pregnant women. Also, the USZPR could introduce selection bias if pregnancies with fetal abnormalities are more likely to receive Zika testing.

The authors note that in 2016, the CDC funded 45 local, state, and territorial surveillance programs for birth defects potentially related to Zika. These programs will continue to monitor the effect of Zika in the coming years.

Morb Mortal Wkly Rep. 2017;66(8):219-222. Full text

For more news, join us on Facebook and Twitter


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.