Susan Mayor/The BMJ

Zika virus in utero is causally associated with microcephaly in infants, showed preliminary results from the first case-control study to investigate whether Zika virus infection during pregnancy can result in microcephaly.

The Brazilian Ministry of Health requested that a study be undertaken to investigate the causes of the microcephaly epidemic after declaring it a national public health emergency in November 2015. It was assumed that the relation between Zika virus and microcephaly was causal, but this had previously not been tested in studies with appropriate control groups.

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