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Head size not always indicative of Zika-related abnormalities
Among newborns initially investigated for microcephaly related to Zika virus, one in five were found to have normal sized heads, yet some had brain abnormalities, according to recent study findings.
“The finding of several newborn babies with neuroimaging abnormalities despite normal sized heads suggests that the initial focus on microcephaly was too narrow,” Giovanny V.A. França, PhD, secretary of health surveillance at the Brazil Ministry of Health, and colleagues wrote. “We believe that under-reporting of microcephaly cases is rare, but newborn babies affected late in pregnancy might fail to be reported as their heads will be in the normal range.”
As of June 4, the Brazilian Ministry of Health (MOH) has reported 7,830 suspected cases of microcephaly, the researchers wrote. Published case series, however, have included up to only 104 children.
To assess a larger cohort of newborns suspected to have microcephaly, França and colleagues performed a retrospective analysis of 1,501 newborns in Brazil who were initially assessed between November 2015 and February. The researchers classified these newborns by diagnostic certainty of Zika and described their prognosis and their clinical and anthropometric traits. Definite Zika cases had laboratory evidence of viral infection; highly probable cases had neuroimaging findings as well as negative lab results for other congenital infections; moderately probable cases also had neuroimaging findings but no negative lab results; somewhat probable cases had neuroimaging findings that were not reported in detail by local teams; and all other cases were discarded.
Of the 1,501 cases of microcephaly, 602 were determined to be definitely or probably due to Zika virus. These included 76 considered definite, 54 highly probable, 181 moderately probable, and 291 somewhat probable. Compared with these groups, the discarded cases had a larger head circumference, a lower first-week mortality rate, and the mothers were less likely to have a rash during pregnancy (20.7% vs. 61.4%). Rashes in the third trimester were associated with brain abnormalities despite normal sized heads. One in five definite or probable cases had normal sized heads. In addition, one in three definite or probable cases had no history of rash during pregnancy.
“Knowledge about Zika virus congenital syndrome is quickly evolving,” the researchers wrote. “There is no question, however, that just as our review shows that most suspected cases ended up being normal newborn babies with small heads, focusing on microcephaly alone will underestimate the true magnitude of this major epidemic.” – by Will Offit
Disclosure: The researchers report no relevant financial disclosures.