Associations of water quality with cholera in case-control studies: a systematic review and meta-analysis

Cholera is a significant health risk for low- and middle-income countries (LMIC), and the threat of outbreaks is likely to increase due to climate change. To keep up to date with the link between water quality and cholera, we conducted a systematic review and meta-analysis to update a previous review while only focusing on water-related exposures. We searched Embase, Web of Science and PubMed for literature published between 2016 and 2022. Search terms were consistent with the previous review. Study quality was assessed using the Risk Of Bias In Non-randomized Studies - of Exposures (ROBINS-E). Water-related exposures were categorized according to the WHO/UNICEF Joint Monitoring Program for Water Supply, Sanitation and Hygiene (JMP) and further divided by the service ladder. Odds ratios were extracted and pooled by performing random-effects meta-analysis. We identified 22 new eligible studies and analysed them in addition to the 45 studies included in the previous review. Analyses revealed higher odds of cholera when consuming sachet water (OR = 1.69, 95% CI: 1.13 to 2.52), unimproved water (OR = 2.91, 95% CI: 1.21 to 7.02), surface water (OR = 3.40, 95% CI: 2.52 to 4.58), and untreated water (OR = 2.51, 95% CI: 2.03 to 3.10). Meanwhile, treating water (OR = 0.42, 95% CI: 0.27 to 0.65) by boiling (OR = 0.38, 95% CI: 0.17 to 0.84) or chlorination (OR = 0.37, 95% CI: 0.17 to 0.83), and drinking basic water (OR = 0.44, 95% CI: 0.27 to 0.69) showed protection. Water-related exposures were prioritized to synthesize the evidence on cholera transmission through drinking water, with sanitation and hygiene as additional risk factors. While the JMP service ladder provided a useful classification framework, context-specific differences in infrastructure and interpretation should be considered when evaluating these findings. Pooled estimates changed with updated evidence while qualitative insights on the protective or risk factors remain valid. Relatively low-cost methods like boiling or chlorinating water provide good protection comparable to providing basic water to the public.