Zika Virus Infection and Associated Neurologic Disorders in Brazil

To the Editor: The first cases of a new illness involving fever and rash that was deemed to have been caused by Zika virus (ZIKV) infection in Brazil were reported in 2014, and the presence of the virus was confirmed in April 2015. In October 2015, an unusual increase in the number of cases of microcephaly among newborn infants was reported in Brazil; this disorder was apparently linked to ZIKV infection. From the first investigations of microcephaly, and from subsequent studies in Brazil and elsewhere, it is now clear that ZIKV is a cause of a range of neurologic disorders, including the Guillain-Barr syndrome (GBS) in adults and abnormalities in fetuses and newborn infants, including microcephaly. 1 Here, we use routinely collected surveillance data and medical records to show how the spread of ZIKV in Brazil was associated with an increase in the incidence of GBS and microcephaly during 2015 and 2016. We also highlight the limitations of routinely collected data, which cannot yet explain, for example, why there were many fewer cases of microcephaly than expected in 2016.