Is congenital cytomegalovirus a leading cause of microcephaly?


The 2016 Zika epidemic made microcephaly a common term, but a new investigation indicates that congenital cytomegalovirus, which is much less studied, could be an even bigger cause of the birth defect.

Congenital cytomegalovirus is a common source of birth defects. Microcephaly has been a birth defect that received a lot of media attention in 2016 because of the Zika virus epidemic. A new investigation in JAMA Pediatrics looks at how many cases of microcephaly occur as a result of congenital microcephaly and how that number of cases could be more than were found to be linked to the 2016 Zika epidemic.1

Investigators ran a population-based cohort study that included pregnant women and their offspring who had been identified in 2 insurance claims databases in the United States: IBM Researcher MarketScan, which included data for employer-sponsored private health insurance, and Medicaid Analytic eXtract. Every pregnancy that ended with a live delivery to a woman with full health birth was included.

There were a total of 2,338,580 pregnancies included in the cohort. Among these pregnancies, there were 336 infants who had a congenital cytomegalovirus diagnosis. The prevalence of microcephaly among infants with a congenital cytomegalovirus diagnosis was 655 per 10,000 live birth and it was 2.8 per 10,000 among newborns without a congenital cytomegalovirus diagnosis (prevalence ratio [PR], 232; 95% CI, 154-350). Following restricting to cytomegalovirus-test newborns, 572 individuals, to correct for preferential testing, the PR was 15 (95% CI, 5.2-41). This PR is biased if other congenital cytomegalovirus-related outcomes trigger testing as congenital cytomegalovirus prevalence in tested infants would overestimate it in the source population. This meant that the researchers compared the prevalence of congenital cytomegalovirus in overall infants with microcephaly to an external unbiased sample of US infants who were screened at birth to get an estimated PR of 7.4 (95% CI, 4.8-11.5) to serve as a conservative lower bound.

The researchers concluded that a congenital cytomegalovirus infection increases the prevalence of microcephaly at delivery by at least 7-fold. The researchers believe that preventing cytomegalovirus in pregnancy could be a substantial way to shrink the number of newborns who are born with microcephaly as well as other outcomes linked to congenital cytomegalovirus, such as hearing loss, in the United States.


1. Messinger C, Lipsitch M, Bateman B, et al. Association between congenital cytomegalovirus and the prevalence at birth of microcephaly in the United States. JAMA Pediatr. September 14, 2020. Epub ahead of print. doi:10.1001/jamapediatrics.2020.3009

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