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Microcephaly in Brazil May Not Just Be Due to Zika Virus Infection :

January 8, 2018

We were all deeply concerned about the infants born with microcephaly attributed to the Zika virus in Brazil.

We were all deeply concerned about the infants born with microcephaly attributed to the Zika virus in Brazil. Yet what is the baseline prevalence of microcephaly in Brazil before and after the Zika epidemic and were there other risk factors that might be playing a role in the overall prevalence of infants born with microcephaly? Silva et al. (10.1542/peds.2017-0589) investigated this question using population-based surveillance methods from two Brazilian birth cohorts in two different cities in Brazil in 2010 before the Zika epidemic manifested itself. The authors used formal working definitions for microcephaly and found that in both cities the prevalence of severe microcephaly ranged from .5 to .7% (higher than expected) suggesting microcephaly was endemic in both municipalities before the current Zika epidemic. In addition, the authors noted that other factors were associated with microcephaly back in 2010 including maternal level of education, marital status, smoking during pregnancy, primiparity, vaginal delivery, and intrauterine growth restriction—all factors not unique to Brazil or to contracting Zika. So what does this mean? 

We asked epidemiologists Elizabeth Dufort and Jennifer White from the New York State Department of Health and Albany Medical College to weigh in with an accompanying commentary (10.1542/peds.2017-3811).  They call for looking at background rates of microcephaly in subpopulations and areas other than Brazil that had an outbreak of Zika as well as look at the risk-factors for microcephaly identified in this study in areas that did not have Zika and again examine baseline rates of this disorder. What is a key takeaway from both the study and commentary is that the methods used to estimate prevalence rates of microcephaly have differed over time, as has the working definition of microcephaly until recently, making attribution of microcephaly largely to a Zika outbreak easier said than proven. If there are other ways we can prevent increasing rates of microcephaly, this study and commentary will energize such activity rather than attribute the problem solely to the work of the Zika virus.

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