Estimating the Health Risks Posed by Intermittent Water Supply Using Quantitative Microbial Risk Assessment

Abstract

Intermittent water supply (IWS) is a prevalent deficiency in piped water supplies. Microbiological and epidemiological evidence indicates that in some contexts IWS is associated with increased levels of fecal contamination and increased risk of waterborne diarrheal disease. In our initial quantitative microbial risk assessment (QMRA) using E. coli counts observed at IWS taps and pathogen to E. coli ratios in sewage, we estimated that IWS could account for 17.2 million infections causing 4.52 million cases of diarrhea, 109,000 DALYs, and 1,560 deaths among the 925 million exposed to IWS globally. Subsequently, we used dead-end ultrafiltation and droplet digital PCR to perform microbial sampling of two IWSs in India and QMRA to estimate the risks to human health attributable to IWS in India. During our microbial sampling in Jaipur, we detected gene targets associated with Cryptosporidium spp., Giardia duodenalis, and enterotoxigenic E. coli (ETEC) concurrently with culturable E. coli in groundwater samples from tube wells. In Nagpur, we observed a significant increase in the proportion of samples positive for culturable E. coli and gene targets associated with waterborne pathogens at household taps served by IWS compared to those served by CWS. At household taps served by IWS we detected genes associated with ETEC, Shigella spp., norovirus GI and GII, adenovirus, Cryptosporidium spp., and Giardia duodenalis. Our QMRA estimates that the daily risks of infection for Giardia, Cryptosporidium, norovirus, adenovirus, and Shigella exceed the US EPA acceptable annual threshold of 1 in 10,000 at the 10th percentile. Collectively, the results of our work indicate that, even given large uncertainty and variability, the public health risks associated with IWS likely exceed acceptable risk levels established by the WHO and US EPA.