Onsite Nonpotable Water Systems Pathogen Treatment Targets: A Comparison of Infection and Disability-Adjusted Life...

Area of Science:

• Environmental microbiology
• Public health risk assessment
• Water reuse safety

Background:

• Onsite nonpotable water systems require pathogen reduction targets to ensure public health.
• Disability-Adjusted Life Year (DALY) is a comprehensive health burden metric.
• Existing benchmarks may not fully capture the nuances of pathogen risk.

Purpose of the Study:

• To calculate pathogen log10 reduction targets (LRTs) for nonpotable water systems using infection (LRT_INF) and DALY (LRT_DALY) benchmarks.
• To evaluate how accounting for illness likelihood, duration, and severity impacts treatment requirements.
• To compare LRTs for Norovirus, Campylobacter jejuni, Cryptosporidium, Giardia, and Salmonella enterica.

Main Methods:

• Utilized annual infection (10^-4 infections per person per year) and DALY (10^-6 DALYs per person per year) benchmarks.
• Employed multilevel dose-response models for Norovirus and Campylobacter jejuni, incorporating probability of illness given infection (Pill|inf).
• Analyzed dose-dependent and dose-independent Pill|inf characterizations using challenge or outbreak data.

Main Results:

• Differences in treatment requirements (LRT_INF - LRT_DALY) were observed, primarily driven by the likelihood of illness.
• For pathogens with dose-independent Pill|inf (e.g., Cryptosporidium), differences were consistent across reuse scenarios.
• Norovirus exhibited the highest LRTs, influenced by high infection risks predicted by the multilevel framework, despite low severity.

Conclusions:

• Illness likelihood is a critical factor in determining pathogen reduction targets for water reuse.
• Updated Norovirus dose-response models and best practices are highlighted.
• Discrepancies exist in scientific understanding of illness versus infection responses across different pathogens.