Impact evaluation of Zika epidemic on congenital anomalies registration in Brazil: An interrupted time series analysis

Abstract

This study aimed to assess the impact of the Zika epidemic on the registration of birth defects in Brazil. We used an interrupted time series analysis design to identify changes in the trends in the registration of congenital anomalies. We obtained monthly data from Brazilian Live Birth Information System and used two outcome definitions: 1) rate of congenital malformation of the brain and eye (likely to be affected by Zika and its complications) 2) rate of congenital malformation not related to the brain or eye unlikely to be causally affected by Zika. The period between maternal infection with Zika and diagnosis of congenital abnormality attributable to the infection is around six months. We therefore used September 2015 as the interruption point in the time series, six months following March 2015 when cases of Zika started to increase. For the purposes of this analysis, we considered the period from January 2010 to September 2015 to be “pre-Zika event,” and the period from just after September 2015 to December 2017 to be “post-Zika event.” We found that immediately after the interruption point, there was a great increase in the notification rate of congenital anomalies of 14.9/10,000 live births in the brain and eye group and of 5.2/10,000 live births in the group not related with brain or eye malformations. This increase in reporting was in all regions of the country (except in the South) and especially in the Northeast. In the period “post-Zika event”, unlike the brain and eye group which showed a monthly decrease, the group without brain or eye malformations showed a slow but significant increase (relative to the pre-Zika trend) of 0.2/10,000 live births. These findings suggest an overall improvement in the registration of birth malformations, including malformations that were not attributed to Zika, during and after the Zika epidemic.

Author summary

Zika can be characterized as one of the most significant emerging arboviruses. The Zika epidemic in Brazil and the subsequent increase in the number of serious brain anomalies, such as microcephaly, has demonstrated the importance of analysing the impact of Zika infection on the rate of congenital anomalies in an affected population. From the analysis of the monthly data on the Live Birth Information System, the authors found that immediately after the Zika event there was a large increase in the notification rate of congenital anomalies reported as a complication of which infection (malformations of brain and eye) and also an increase in the rate of congenital malformations not related with Zika. This growth was seen throughout the country as a whole and in all regions (except in the South), especially in the Northeast where the infection rates were the highest. In the period post-Zika event, the group not related with brain or eye malformation there was an increase in the monthly notification rate while in the brain and eye group there was a decrease in the monthly notification rate. These findings suggest an overall growing awareness of health professionals to improve the registration of birth malformations trigged by the Zika epidemic.