Citation:

Schoen, M., M. Jahne, J. Garland, L. Ramirez, A. Lopatkin, AND K. Hamilton. Quantitative microbial risk assessment of antimicrobial resistant and susceptible Staphylococcus aureus in reclaimed wastewaters. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 55(22):15246-15255, (2021). https://doi.org/10.1021/acs.est.1c04038

Impact/Purpose:

Wastewater and greywater are increasingly reclaimed for potable and non-potable purposes but require treatment to control for a range of human-infectious pathogens. Risk-based pathogen treatment requirements for reuse are calculated to achieve a specific level of health protection for consumers and are typically based on the control of enteric pathogens; however, the microbiota of graywater is dominated by skin-associated bacteria, some of which may be pathogenic, e.g. Staphylococcus aureus. S. aureus is a bacterium that can be a human commensal but is also responsible for minor skin infections as well as potentially fatal blood stream infections. Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to a variety of antimicrobial drugs, while methicillin-susceptible S. aureus (MSSA) responds to treatment. The objective of this work was to use a new framework for modeling environmentally-transmitted antimicrobial resistance to estimate the probability of nasal colonization and subsequent, delayed infection and disease burden resulting from potential exposures to MRSA and MSSA in reclaimed wastewater and graywater considering a range of treatment levels and to compare the predictions to selected health benchmarks. In doing so, we evaluated whether risk-based reuse treatment requirements based on enteric pathogens for non-potable reuse and potable use are also protective against S. aureus. A secondary objective was to identify the dominant mechanisms that influence MRSA exposure in a reuse scenario with horizontal gene transfer occurring in treatment.

Description:

The annual risks of colonization, skin infection, blood stream infection (bsi), and disease burden from exposures to antibiotic resistant and susceptible Staphylococcus aureus (S. aureus) were estimated using quantitative microbial risk assessment. 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 was most sensitive to the treatment log10 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 likely acceptable for risk-based, non-potable or potable reuse systems but possibly unacceptable for exposures to minimally treated GW or WW. Strain specific data to characterize dose-response and concentration in WW are needed to substantiate the QMRA.

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