The impact of weekly rainfall on water-related diseases in The Gambia: a time-series analysis of health facility data

In West Africa, anticipated climatic changes may increase the risk of common water-related diseases, however the evidence is limited. We investigated the risk of diarrheal diseases and skin infections associated with rainfall in rural Gambia, using data on clinic visits (2010-2022) linked to meteorological exposures from the ERA5-Land reanalysis dataset. We conducted time-series regression analysis to assess the risks associated with total weekly rainfall (mm) and weeks with heavy rainfall events (daily rainfall >95th percentile) on diarrheal and skin infection visits, adjusted for weekly average maximum temperature (°C), season and long-term trends. Subgroup analyses were undertaken to examine potential effect modification by age, sex and pathogen category. An increase in weekly total rainfall was associated with an increased risk of both health outcomes, but only up to rainfall values of ∼30/35mm. Over a 0-3 week lag, 20mm of weekly rainfall (versus 0mm) was associated with an increased relative risk of diarrheal (1.20 RR; 95% CI: 1.01-1.43) and skin (1.39 RR; 95% CI: 1.22-1.58) visits. Age modified rainfall-health associations, with patterns differing by outcome. Stronger associations were found in children under-5 for skin infections, while diarrheal risks were higher among patients 5+ years. Rainfall effects were greatest for bacterial skin and diarrheal visits. Heavy rainfall events were not associated with a change in risk for either health outcome. Adjusting for temperature attenuated rainfall effects. These findings show that weather is an important determinant of disease in this population. More investment in climate-resilient water, sanitation and hygiene measures is needed.