Ecological study of human brucellosis in Iran from 2000 to 2023 and the limited role of climatic factors

Human brucellosis remains a major public health issue in endemic regions such as Iran. While climatic variables may affect transmission patterns, their role remains uncertain. This study analyzed long-term trends of human brucellosis in relation to climatic factors in Iran from 2000 to 2023. A time-series ecological design was applied using annual crude incidence rates (CIR) of brucellosis alongside climatic indicators including annual mean temperature (AMT), annual precipitation (AP), and the Standardized Precipitation Evapotranspiration Index (SPEI). Correlation tests, linear regressions, and multivariate models were performed. The average CIR was 23.96 per 100,000. AMT showed an inverse correlation with CIR, while SPEI indicated a weak positive association. Precipitation was not significantly correlated. Multivariate models explained less than one-quarter of variance, and no climatic factor remained a significant predictor. Findings suggest that climatic variables alone have limited explanatory power for brucellosis trends in Iran, with socioeconomic, agricultural, and behavioral factors likely playing a much greater role. Rather than demonstrating a strong climate-disease link, this study highlights the complexity and potential insignificance of climatic influence on brucellosis incidence, underscoring the need for integrated One Health approaches.