Widespread transmission of Zika virus by Aedes mosquitoes has been recognized in Brazil since late 2014, and in October 2015, an increase in the number of reported cases of microcephaly was reported to the Brazil Ministry of Health.* By January 2016, a total of 3,530 suspected microcephaly cases had been reported, many of which occurred in infants born to women who lived in or had visited areas where Zika virus transmission was occurring. Microcephaly surveillance was enhanced in late 2015 by implementing a more sensitive case definition. Based on the peak number of reported cases of microcephaly, and assuming an average estimated pregnancy duration of 38 weeks in Brazil (1), the first trimester of pregnancy coincided with reports of cases of febrile rash illness compatible with Zika virus disease in pregnant women in Bahia, Paraíba, and Pernambuco states, supporting an association between Zika virus infection during early pregnancy and the occurrence of microcephaly. Pregnant women in areas where Zika virus transmission is occurring should take steps to avoid mosquito bites. Additional studies are needed to further elucidate the relationship between Zika virus infection in pregnancy and microcephaly.

Brazilian Ministry of Health, Pan American Health Organization, and Enhancing Research Activity in Epidemic Situations.

A time series analysis by Manish Patel and colleagues shows that the introduction of rotavirus vaccination in Brazil is associated with reduced diarrhea-related deaths and hospital admissions in children under 5 years of age.

OBJECTIVE To propose a method of redistributing ill-defined causes of death (IDCD) based on the investigation of such causes.METHODS In 2010, an evaluation of the results of investigating the causes of death classified as IDCD in accordance with chapter 18 of the International Classification of Diseases (ICD-10) by the Mortality Information System was performed. The redistribution coefficients were calculated according to the proportional distribution of ill-defined causes reclassified after investigation in any chapter of the ICD-10, except for chapter 18, and used to redistribute the ill-defined causes not investigated and remaining by sex and age. The IDCD redistribution coefficient was compared with two usual methods of redistribution: a) Total redistribution coefficient, based on the proportional distribution of all the defined causes originally notified and b) Non-external redistribution coefficient, similar to the previous, but excluding external causes.RESULTS Of the 97,314 deaths by ill-defined causes reported in 2010, 30.3% were investigated, and 65.5% of those were reclassified as defined causes after the investigation. Endocrine diseases, mental disorders, and maternal causes had a higher representation among the reclassified ill-defined causes, contrary to infectious diseases, neoplasms, and genitourinary diseases, with higher proportions among the defined causes reported. External causes represented 9.3% of the ill-defined causes reclassified. The correction of mortality rates by the total redistribution coefficient and non-external redistribution coefficient increased the magnitude of the rates by a relatively similar factor for most causes, contrary to the IDCD redistribution coefficient that corrected the different causes of death with differentiated weights.CONCLUSIONS The proportional distribution of causes among the ill-defined causes reclassified after investigation was not similar to the original distribution of defined causes. Therefore, the redistribution of the remaining ill-defined causes based on the investigation allows for more appropriate estimates of the mortality risk due to specific causes.

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.