Acute Diarrheal Disease Associated With Climate Variability and Water Supply System Configuration: An Ecological Study in Brazil.

Acute diarrheal disease (ADD) remains a major public health problem in low- and middle-income countries, where vulnerabilities in water supply systems (WSSs) are associated with increased exposure to disease. Rainfall patterns influenced by climate change are also associated with changes in ADD occurrence, although evidence on the interaction between ADD, WSS configurations, and climate variability remains limited. This ecological study used water quality indicators, health surveillance records, and generalized linear models to assess associations between different WSS configurations, including conventional treatment systems, disinfection systems, and systems distributing a mixture of treated and raw water. The exponentiated coefficient for systems distributing a mixture of treated and raw water was exp(β) = 1.21 (95% CI: 1.03-1.43; p = 0.032), indicating that ADD rates were 21% higher in these systems than in conventional treatment systems. Similarly, the exponentiated coefficient for the dry season was exp(β) = 0.73 (95% CI: 0.62-0.86; p = 0.001), indicating that ADD rates were 27% lower during the dry season than during the rainy season. Water quality indicators showed no statistically significant association with ADD cases. These findings highlight the importance of improving water treatment infrastructure, particularly in hybrid WSSs, to reduce ADD rates and protect public health.