Birth defects potentially linked to cases of Zika virus in the United States have increased by a factor of nearly 20 since the virus first made its way into the country, according to new findings by the Centers for Disease Control and Prevention.
“The higher proportion of these defects among pregnancies with laboratory evidence of Zika infection in USZPR [U.S. Zika Pregnancy Registry] supports the relationship between congenital Zika virus infection and these birth defects,” wrote the authors of a new report led by Janet D. Cragan, MD, of the National Center on Birth Defects and Developmental Disabilities at the CDC (MMWR Morb Mortal Wkly Rep. 2017;66:219-22).
Dr. Cragan and her coauthors retrospectively examined data on birth defects in three regions of the country: Massachusetts during 2013, North Carolina during 2013, and Atlanta during 2013-2014. The investigators focused on birth defects associated with prenatal Zika virus infections, mainly brain abnormalities and microcephaly.
The rate of total birth defects across the three regions was 2.86 per 1,000 live births, with 747 infants and fetuses identified as having one or more defects. Microcephaly and brain abnormalities alone occurred at a rate of 1.50 per 1,000 live births, with eye abnormalities and central nervous system dysfunction also occurring.
These numbers are relatively low when compared with data from Jan. 15 through Sept. 22, 2016. The birth defect rate jumped up to 58.8 per 1,000 live births, according to data from the USZPR, which found evidence of 26 infants and fetuses with brain or cranial defects in 442 completed pregnancies. These infants were all born to mothers with laboratory-confirmed Zika virus infections.
“Among 410 (55%) infants or fetuses with information on the earliest age a birth defect was recorded, 371 (90%) had evidence of a birth defect meeting the Zika definition before age 3 months,” the authors explained. “More than half of those with brain abnormalities or microcephaly or with neural tube defects and other early brain malformations had evidence of these defects noted prenatally (55% and 89%, respectively).”
Dr. Cragan and her colleagues hope that this evidence will further solidify the link between Zika virus and birth defects and pave the way for more population-based studies.
“These data demonstrate the critical contribution of population-based birth defects surveillance to understanding the impact of Zika virus infection during pregnancy,” the authors concluded. “In 2016, CDC provided funding for 45 local, state, and territorial health departments to conduct rapid population-based surveillance for defects potentially related to Zika virus infection, which will provide essential data to monitor the impact of Zika virus infection in the United States.”