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Measuring Infant Head Circumference Not Enough to Detect Zika Damage

October 11th, 2016

PELOTAS, BRAZIL — Microcephaly screening alone is not sufficient to accurately diagnose Zika virus infection in newborns, according to new Brazilian research.

The largest study of its kind to date was published recently in The Lancet. The Universidade Federal de Pelotas-led research recommends, instead, that screening criteria used by neonatal units also include signs and symptoms of brain abnormalities, regardless of head circumference.

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"Our study, which included all suspected cases of microcephaly in newborns in Brazil up to February, discarded three out of five cases after a full investigation as most suspected cases ended up being normal newborn babies with small heads,” explained lead author Cesar G. Victora, MD. “However, one in five definite or probable Zika cases had head circumference values in the normal range. Therefore, the current focus on microcephaly screening alone is too narrow.”

Zika virus is known to cause microcephaly, a birth defect marked by smaller head and brain size. Victora and colleagues used data from a Brazilian Ministry of Health (MOH) surveillance system, which has been hard-hit by the infection, to monitor nearly 6,000 suspected cases of microcephaly based on head circumference.

The researchers sought to determine the clinical — including sex, gestational age, imaging findings, maternal history of rash, and mortality — and anthropometric — including head circumference and birthweight — characteristics of live births.

The team focused on 1,501 live born cases that had been fully investigated by the MOH, with suspected cases divided into five categories according to diagnostic certainty of Zika infection: definite, highly probable, moderately probable, somewhat probable, and discarded (not deemed to be Zika).

Results indicate that, compared to 899 cases that were discarded, the 602 definite or probable cases had small head circumference at birth and their mothers had been more likely to experience a rash during pregnancy — 21% vs. 61%. Those babies also were four times more likely to die in the first week of life.

The study also reports that rashes in late pregnancy were linked with brain abnormalities, despite normal head sizes. Study authors point out that development of the cranium mostly occurs by week 30, so children with brain damage can be born with normal-sized heads, adding that their research raises the possibility that Zika virus infection in newborn babies might lead to brain damage.

The researchers emphasize that more than 100 of the definite or probable cases had head circumferences within normal range and would not have been included in an analysis for Zika if more limited cutoffs had been used.

“Zika virus congenital syndrome is a new teratogenic disease,” study author concluded. “Because many definite or probable cases present normal head circumference values and their mothers do not report having a rash, screening criteria must be revised in order to detect all affected newborn babies.”

Victora added, "Our findings suggest that among pregnancies affected by Zika virus, some foetuses will have brain abnormalities and microcephaly, other will have abnormalities with normal head sizes, and others will not be affected. A surveillance system aimed at detecting all affected newborns should not just focus on microcephaly and rash during pregnancy and should be revised, and examination of all newborns during epidemic waves should be considered."