Sensitivity of quantitative microbial risk assessments to assumptions about exposure to multiple consumption events per day

Quantitative microbial risk assessments (QMRAs) of contaminated drinking water usually assume the daily intake volume is consumed once a day. However, individuals could consume water at multiple time points over 1 day, so the objective was to determine if the number of consumption events per day impacted the risk of infection from Campylobacter jejuni during short-term contamination events. A probabilistic hydraulic and risk model was used to evaluate the impact of multiple consumption events as compared to one consumption event on the health risk from the intake of contaminated tap water. The fraction of the population that experiences greater than 10⁻⁴ risk of infection per event at the median dose was 6.8% (5th–95th percentile: 6.5–7.2%) for one consumption event per day, 18.2% (5th–95th: 17.6–18.7%) for three consumption events per day, and 19.8% (5th–95th: 14.0–24.4%) when the number of consumption events varied around 3.49 events/day. While the daily intake volume remained consistent across scenarios, the results suggest that multiple consumption events per day increases the probability of infection during short-term, high level contamination events due to the increased coincidence of a consumption event during the contamination peak. Therefore, it will be important to accurately characterize this parameter in drinking water QMRAs.