Spatiotemporal dynamics of Zika in Brazil, 2016-2023: a nationwide population-based study

The Zika epidemic was first reported in Brazil in 2015. Since then, several factors have sustained the virus transmission chain in the country. This study aimed to describe the epidemiological profile and temporal trends, as well as to identify significant spatial and spatiotemporal clusters of Zika in Brazil between 2016 and 2023.

Ecological study including confirmed Zika cases in Brazil from 2016 to 2023. Data were extracted from the National Notifiable Diseases Information System. Sociodemographic variables (age, sex, race/ethnicity, education level, and pregnancy status) were collected, along with incidence rates. Analyses were conducted in three steps: (1) description of the epidemiological profile; (2) temporal analysis: Joinpoint regression modeling was applied to identify trends and the Average Annual Percent Change (AAPC) was calculated with 95% confidence intervals and 5% significance level; (3) spatial analysis: spatial dependence among municipalities was assessed using the Global Moran's I index, followed by spatial scan statistics to identify spatial clusters of virus transmission, using both purely spatial and spatiotemporal analyses.

A total of 176,122 cases were reported during the study period. Among them, 42.27% (n = 74,458) were aged 20-39 years, 66.96% (n = 117,945) were female, and 34.92% (n = 61,513) were mixed-race. A decreasing trend in incidence rates was observed in Brazil (AAPC - 36.55%; p < 0.001), with disparities across states. Fifteen out of 27 states showed a downward trend. Rio Grande do Norte was the only state to exhibit an increasing incidence trend and was also identified as the area with the highest relative risk of Zika infection in the country (RR = 12.1; p < 0.001). In the spatio-temporal analysis, the cluster with the highest relative risk (RR 31.08; p < 0.001) included 2,770 municipalities across the North, Northeast, Southeast, and Central-West regions.

Zika cases predominated among adults, females, and mixed-race individuals. In Brazil, the overall incidence rate showed a decreasing trend during the study period. The Northeast and Central-West regions had the largest number of clusters, highlighting the need to strengthen surveillance activities in these areas to reduce transmission rates.