Systematic reviews are a rigorous knowledge synthesis technique first developed in the health sciences to summarize information from numerous randomized trials examining the clinical efficacy of an intervention. In contrast to a narrative review, this method permits the evaluation of all available evidence on the question of interest using a standardized process. Because of varied opinions regarding the evidence for sources of antibiotic resistance found in the environment, this app9roach is ideally suited to this type of topic. We conducted a systematic review to address the following question: : Is the prevalence or concentration of antibiotic resistant bacteria (ARB) or resistance genes (ARG) in soil, water, air or free-living wildlife higher in close proximity to, or downstream from, known or suspected sources compared to areas more distant from or upstream from these sources? The total number of studies that were evaluated was 4,524, and from these, 60 were included in the final evaluation (19 with ARG outcome and 41 with ARB outcome). Many of the studies provided little useful information due to a high level of bias in the study design. The systematic review found a large number of studies presenting qualitative evidence that proximity to or direction from point sources, particularly waste water treatment plants, may be associated with higher levels of antibiotic resistance; however, very few studies quantitatively characterize this effect or provide statistical inference to aid in interpretation. This systematic review provides a strong imperative to improve research methods in order to provide interpretable, quantitative information about the effect of point sources on resistance in the environment.
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