Quantitative Microbial Risk Assessment of Antimicrobial Resistant and Susceptible Staphylococcus aureus in Reclaimed Wastewaters

The annual risks of colonization, skin infection, bloodstream infection (BSI), and disease burden from exposures to antibiotic-resistant and susceptible Staphylococcus aureus (S. aureus) were estimated using quantitative microbial risk assessment (QMRA). We estimated the probability of nasal colonization after immersion in wastewater (WW) or greywater (GW) treated across a range of treatment alternatives and subsequent infection. Horizontal gene transfer was incorporated into the treatment model but had little effect on the predicted risk. The cumulative annual probability of infection (resulting from self-inoculation) was most sensitive to the treatment log(10) reduction value (LRV), S. aureus concentration, and the newly calculated morbidity ratios and was below the health benchmark of 10(-4) infections per person per year (ppy) given a treatment LRV of roughly 3.0. The predicted annual disability-adjusted life years (DALYs), which were dominated by BSI, were below the health benchmark of 10(-6) DALYs ppy for resistant and susceptible S. aureus, given LRVs of 4.5 and 3.5, respectively. Thus, the estimated infection risks and disease burdens resulting from nasal colonization are below the relevant health benchmarks for risk-based, nonpotable, or potable reuse systems but possibly above for immersion in minimally treated GW or WW. Strain-specific data to characterize dose-response and concentration in WW are needed to substantiate the QMRA.

Automated summary

This study used quantitative microbial risk assessment to estimate the risks associated with antibiotic-resistant and susceptible Staphylococcus aureus colonization and found that the probability of infection was most sensitive to treatment log reduction value, S. aureus concentration, and morbidity ratios. The estimated infection risks and disease burdens were below health benchmarks for certain reuse systems, but potentially higher for exposure to minimally treated greywater or wastewater. Further strain-specific data are needed to validate the QMRA.