Geographic and Environmental Determinants of Acute Watery Diarrhea Burden in Bangladesh: A 10-Year Ecological Analysis of Flood Exposure and Divisional Disease Incidence (2014–2024)

Background: Acute watery diarrhea (AWD) remains a leading public health burden in Bangladesh, exacerbated by annual monsoon flooding that contaminates water sources and inundates sanitation infrastructure. However, no 10-year multi-divisional analysis has quantified the association between flood exposure and AWD incidence across all eight administrative divisions. Methods: We conducted an ecological panel study using division-year observations (n = 88) from 2014 to 2024. AWD case estimates were derived from the Bangladesh Ministry of Health and Family Welfare (MoHFW) DHIS2 data repository and national IEDCR cholera sentinel surveillance, scaled to DGHS Control Room reference totals. Flood duration data were derived from published BWDB flood severity classifications. We applied STL seasonal decomposition, Spearman rank correlation, cross-correlation function (CCF) lag analysis, and negative binomial regression with log-population offset. Results: Estimated national AWD cases ranged from 2,080,001 (2020, COVID disruption) to 4,224,002 (2017, severe flood), with a mean of 3,520,000 per year. Severe flood years (2017, 2022) had 23.8% higher AWD burden than non-severe years. Division-level incidence ranged from 4,455 (Barishal) to 1,151 (Rangpur) per 100,000 per year. STL decomposition identified August as the peak AWD month. Rainfall preceded AWD surges by 0–1 months nationally (r = 0.914, p < 0.001). Barishal had significantly higher AWD incidence than Dhaka (IRR = 2.56, 95% CI: 2.55–2.56, p < 0.001). Conclusions: AWD burden in Bangladesh shows strong seasonal and geographic patterning consistent with flood and monsoon exposure. Barishal and Sylhet divisions carry the highest incidence. Anticipatory WASH responses and targeted investment in high-burden divisions are needed.