Surveillance of Zika virus infection and microcephaly in Brazil

846 www.thelancet.com Vol 388 August 27, 2016 Zika virus has been spreading rapidly in Brazil and the Americas, with a sharp increase in the number of notifi ed microcephaly cases since September, 2015. Based on the high number of cases, and the association between Zika virus infection and microcephaly, WHO on Feb 1, 2016, declared a Public Health Emergency of International Concern. Recently, animal models have shown that the Brazilian Zika virus strain causes intrauterine growth restriction and microcephaly. An emerging disease such as Zika virus infection, with severe consequences for newborn babies, is already a major challenge for public health authorities for countries as large as Brazil. But the eff ect of the current epidemic is expected to be even more devastating, considering the current Brazilian economic crisis and its potential impact on the already chronically underfunded Brazilian health system. Eff ective evidence-based health surveillance systems are needed. In the context of several scientifi c and public health uncertainties regarding Zika virus infection, Giovanny França and colleagues’ paper in The Lancet is welcome. Using data from the Brazilian Ministry of Health surveillance system for microcephaly, the study describes clinical and anthropometric characteristics of the largest case series of suspected Zika virus infection reported so far. Among a total of 5554 liveborn infants with suspected microcephaly, the study includes data for all 1501 suspected cases (27%) with a complete investigation. Compared with discarded cases (all cases that were not included in the categories as probable cases; n=899), defi nite and probable cases (n=602) showed smaller head circumference and their mothers were more likely to refer rash during pregnancy. Interestingly, some 20% of the defi nite or probable cases had normal head circumference values, and for a third of them, a rash had not occurred during pregnancy. Based on these results, the authors recommend that a surveillance system aimed at detecting all aff ected newborn babies should not simply focus on microcephaly and rash during pregnancy. The paper by França and colleagues is an important contribution for improving the surveillance system for congenital Zika virus infection. However, caution should be taken in interpreting results of this case series based on routinely collected data with missing information for many cases and an unknown degree of under-reporting. Based on the cutoff for head circumference below –2 SD (Z values, InterGrowth standards), the study provides a sensitivity estimate of 83% for identifying defi nite or probable cases. There is potential bias in the estimates provided for sensitivity and specifi city due to the way that participants were selected for the study. Most participants included in the analyses were reported on the basis of a preselection screening for microcephaly, a predictor of congenital Zika virus syndrome. Because small head circumference is being evaluated as an indicator, the incorporation of a correlate (microcephaly) in the selection of participants might have overestimated sensitivity. Systematic follow-up studies during pregnancy and the fi rst years of life will be needed to provide more accurate sensitivity estimates of the proposed criterion. Concerning specifi city, the authors’ estimate of 98% is also debatable. Based on the InterGrowth standards, one would truly expect 2% of normal newborn babies having microcephaly using the proposed cutoff . However, 98% is not the expected specifi city for ruling out congenital Zika virus syndrome among suspected cases, but the specifi city for pathological microcephaly. For incorporating new information besides microcephaly and rash during pregnancy to detect all aff ected cases, neurological signs and symptoms could be eligible, but might be diffi cult to obtain in most settings because of insuffi cient specialised personnel. The development of an accurate serological test that Surveillance of Zika virus infection and microcephaly in Brazil