Microcephaly in Brazil: how to interpret reported numbers?

Brazil is facing its first outbreak of Zika virus, particularly in the northeast region. Most cases of Zika virus infection are self-limited and without sequelae, but there have been clusters of cases of microcephaly in some areas of known Zika virus transmission. Although strongly suspected, the causal relation between in-utero exposure to Zika and microcephaly is yet to be established. The increased number of microcephaly cases in Brazil has led to a high level of concern among pregnant women throughout the country.