Risk assessment is critical for identifying target concentrations of antibiotic resistant pathogens necessary for mitigating potential harmful exposures associated with water reuse. However, there is currently limited available data characterizing the concentrations of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in recycled water to support robust efforts at risk assessment. The objective of this systematic review was to identify and synthesize the existing literature documenting the presence and abundance of ARB and ARGs in recycled water. In addition, this review identifies best practices and explores monitoring targets for studying ARB and ARGs in recycled water to guide future work and identifies key research needs aimed at better supporting quantitative microbial risk assessment focused on recycled water and antibiotic resistance. Future efforts to collect data about ARB and ARG prevalence in recycled water should report concentration data per unit volume. Sample metadata should also be provided, including a description of treatment approach, a description of planned water uses (e.g., potable, irrigation), methods for conveyance to the point of use, and available physicochemical water quality data. Additional research is needed aimed at identifying recommended ARB and ARG monitoring targets and for developing approaches to incorporate metagenomic data into risk assessment.@en

Antibiotic-resistant bacteria and antibiotic resistance genes are abundant in stormwater, yet there is no consensus regarding how to assess their public health risks. We systematically reviewed the literature and identified 15 studies that provided quantitative occurrence and/or abundance information that was linked to stormwater. Sampling and data analysis approaches across studies varied widely, emphasizing that standardized approaches are needed to pool data across studies in a risk analysis. The amounts, timing, and intensity of precipitation within the storm sewershed for fate and transport were rarely considered and/or reported in relation to concentrations of resistance determinants among the reviewed studies. Linking hydrologic and sewershed characteristics to microbial community composition and antibiotic resistance determinants may help improve our understanding of risk and improve sampling protocols. Research needs for ARB and ARG quantification and assessment are discussed, with an emphasis on informing quantitative microbial risk assessments.

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