Zika Virus Infection and Associated Neurologic Disorders in Brazil

Abstract

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-Barré 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. To explore the temporal and geographic distribution of ZIKV infection, we used data provided by municipalities and states in each of the five regions of Brazil, as compiled by the Ministry of Health. These data describe the number of suspected and confirmed cases of ZIKV infection and of cases reported as GBS and microcephaly (Sections 1 and 2 in the Supplementary Appendix, available with the full text of this letter at NEJM.org). Disclosure forms provided by the authors are available with the full text of this letter at NEJM.org.