Recreational Water Risk from Extended-Spectrum Beta-Lactamase-Producing Escherichia coli of Broiler Origin: A Quantitative Microbial Risk Assessment

Extended-spectrum beta-lactamase (ESBL)-producing E. coli from broiler farms can reach watersheds used for recreational swimming. We assessed short-term swimmer exposure by extending a modular quantitative microbial risk assessment (QMRA) to the recreational water pathway linking land manure application to in-stream fate and transport with dilution and decay. We modeled single-event exposure doses and estimated loss of disability-adjusted life years (DALYs). We ran sensitivity analyses on several parameters and compared outputs to published recreational water assessments that include ESBL E. coli. Assuming a worst-case scenario, single-event doses were lower for adults (2.95 CFU; UI 0.14–6.11) and higher for children (8.78 CFU; UI 0.56–17.20) on day 1 after land application, then dropped below 0.01 CFU by day 200, with DALY losses from 10−7 to 10−10. Uncertainty was dominated by fate and transport. Stronger particle binding, faster in-stream decay, and larger effective volumes lowered exposure, while higher shedding, greater flow, and larger wash-off raised it. Estimates fell at the low end of prior studies. Swimmer exposure appears to be extremely low and short-lived. The modular QMRA links farm contamination to bathing-site risk and supports risk-based monitoring (after spreading or storms) and short-term forecasts that focus advisories on short, higher-risk windows after litter application.