Preliminary findings of the study are being reported because of the striking magnitude of the association between microcephaly and Zika virus infection.

A case-control study was just released online in The Lancet Infectious Diseases by Brazilian researchers examines the association between microcephaly and in-utero Zika virus infection, investigated by molecular and serological methods in cases of microcephaly and their controls at time of birth.

The prospective study was performed in the metropolitan region of Recife in Pernambuco State, the hotspot of the microcephaly epidemic in Brazil, between January and May, 2016.

Researchers plan to test many more, but their preliminary findings show that 80% of the women who had babies with microcephaly tested positive for Zika virus infection, compared to 64% of women whose babies had normal-sized heads.

And among the babies, 51% with microcephaly tested positive for Zika. None of the normal babies did.

“We conclude that the microcephaly epidemic is a result of congenital Zika virus infection,” the team wrote in their report, published in Lancet Infectious Diseases.


The microcephaly epidemic, which started in Brazil in 2015, was declared a Public Health Emergency of International Concern by WHO in 2016. Researchers reported the preliminary results of a case-control study investigating the association between microcephaly and Zika virus infection during pregnancy.


The study was performed in eight public hospitals in Recife, Brazil. Cases were neonates with microcephaly. Two controls (neonates without microcephaly), matched by expected date of delivery and area of residence, were selected for each case. Serum samples of cases and controls and cerebrospinal fluid samples of cases were tested for Zika virus-specific IgM and by quantitative RT-PCR. Laboratory-confirmed Zika virus infection during pregnancy was defined as detection of Zika virus-specific IgM or a positive RT-PCR result in neonates.

Maternal serum samples were tested by plaque reduction neutralisation assay for Zika virus and dengue virus. We estimated crude odds ratios (ORs) and 95% CIs using a median unbiased estimator for binary data in an unconditional logistic regression model. We estimated ORs separately for cases with and without radiological evidence of brain abnormalities.


Between Jan 15, 2016, and May 2, 2016, the researchers prospectively recruited 32 cases and 62 controls. 24 (80%) of 30 mothers of cases had Zika virus infection, compared with 39 (64%) of 61 mothers of controls (p=0·12). 13 (41%) of 32 cases and none of 62 controls had laboratory-confirmed Zika virus infection; crude overall OR 55·5 (95% CI 8·6–∞); OR 113·3 (95% CI 14·5–∞) for seven cases with brain abnormalities; and OR 24·7 (95% CI 2·9–∞) for four cases without brain abnormalities.

Source: The Lancet Infectious Diseases