Onsite Nonpotable Water Systems Pathogen Treatment Targets: A Comparison of Infection and Disability-Adjusted Life Years (DALYs) Risk Benchmark Approaches

Calculatedwater system treatment requirements for entericpathogens based on achieving a health burden benchmark that accountsfor the likelihood and severity of illness were less than those basedon an annual probability of infection benchmark only when there wasevidence of a small likelihood of illness at low doses. Pathogen log(10) reduction targets for onsitenonpotablewater systems were calculated using both annual infection (LRTINF) and disability-adjusted life year (LRTDALY)benchmarks. The DALY is a measure of the health burden of a disease,accounting for both the severity and duration of illness. Resultswere evaluated to identify if treatment requirements change when accountingfor the likelihood, duration, and severity of illness in additionto the likelihood of infection. The benchmarks of 10(-4) infections per person per year (ppy) and 10(-6) DALYsppy were adopted along with multilevel dose-response modelsfor Norovirus and Campylobacter jejuni, which characterize the probability of illness given infection (Pill|inf)as dose-dependent using challenge or outbreak data. We found differencesbetween treatment requirements, LRTINF - LRTDALY, for some pathogens, driven by the likelihood of illness,rather than the severity of illness. For pathogens with dose-independentPill|inf characterizations, such as Cryptosporidium spp., Giardia, and Salmonella enterica, the difference, LRTINF - LRTDALY,was identical across reuse scenarios (

Automated summary

Calculated water system treatment requirements for enteric pathogens differ depending on whether the likelihood and severity of illness are considered in addition to the probability of infection. The study used infection and disability-adjusted life year (DALY) benchmarks to calculate log(10) reduction targets for on-site non-potable water systems. It was found that the differences in treatment requirements were driven by the likelihood of illness, rather than the severity of illness, for certain pathogens.