Socioeconomic, climatic, and sanitary conditions of Brazilian municipalities and their relationship with the incidence of Zika and microcephaly

Zika and microcephaly cases in Brazil showed uneven regional distribution, with underlying causes still unclear. Socioeconomic, climatic, and sanitary disparities may explain these patterns. This study analyzed the relationship between these factors and the occurrence of Zika virus (ZIKV) and microcephaly epidemics. Data on cases reported in 2016 were obtained from the Ministry of Health, Brazilian Institute of Geography and Statistics, and Unified Registry for Social Programs, along with sanitary, socioeconomic, and climatic indicators. Incidence rates were calculated and smoothed using the local empirical Bayesian method. Spatial distribution was evaluated with thematic maps and Moran's I statistics, revealing significant autocorrelation for ZIKV and microcephaly. Associations with extreme weather events were tested using the U-test, showing that municipalities experiencing droughts were most affected (ZIKV: median = 31.06 vs. 21.13; microcephaly: 1.73 vs. 1.31; p < 0.001). Sanitary and socioeconomic influences were explored through hybrid clustering (Ward's method + k-means). Group differences assessed with the U-test were significant (p < 2.2 × 10⁻¹⁶). Municipalities in Group 1, characterized by lower socioeconomic and sanitary indices, had reduced access to sewage collection (9-12% vs. 72-78%), solid waste services (66-67% vs. 95-96%), and piped water (65% vs. 90%), while presenting higher ZIKV (median = 43.9 vs. 13.4) and microcephaly incidences (median = 1.4 vs. 1.0). Findings suggest that structural vulnerabilities, compounded by drought, influence the spatial dynamics of ZIKV and microcephaly. These results highlight the importance of addressing inequalities in sanitary and socioeconomic infrastructure to guide public health strategies and mitigate future epidemics.