Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/3/2023
Publication Date: 6/18/2023
Citation: Burch, T.R., Stokdyk, J.P., Durso, L.M. 2023. Exposure rates for ingestion of antibiotic resistance genes from rural private wells contaminated by human and livestock fecal sources. Meeting Abstract. June 15-19, 2023.
Technical Abstract: Antibiotic resistance (AR) is a public health problem with human, agricultural, and environmental dimensions. Quantitative microbial risk assessment (QMRA) could be used for prioritizing policy and management decisions in these sectors, but few QMRAs exist for AR because dose-response models to estimate probability of infection and/or illness are lacking for most AR hazards. This study used QMRA to estimate the likelihood of ingesting class 1 integron genes (intI1) and five antibiotic resistance genes (ARGs: erm(B), sul1, tet(A), tet(W), and tet(X)) in drinking water from private wells contaminated by human and/or livestock fecal sources. Though ingestion of ARGs is not directly associated with infection, they serve as an indicator of AR bacteria. Quantitative PCR was used to measure ARGs and microbial source-tracking (MST) markers in 138 private well-water samples collected over 4 seasons from a rural county in northeast Wisconsin. Source tracking markers included 5 human-specific markers and 6 bovine-specific markers. Daily probabilities of ingestion were a direct function of measured ARG concentrations, and point estimates varied from 0% to 66% depending on gene target and fecal source. Compared to wells in which both types of MST marker were absent, three genes had statistically significant increased daily probabilities of ingestion when MST markers were present. These included erm(B) in the presence of bovine-specific fecal material (12% [95% CI: 0.1-29%]); tet(A) in the presence of bovine-specific (39% [22-56%]), human-specific (31% [11-55%]), and both types of fecal material simultaneously (49% [25-65%]); and tet(W) in the presence of both types of fecal material simultaneously (41% [16-58%]). Ingestion rates of intI1, sul1, and tet(X) were not significantly greater in wells where MST markers were present compared to those where they were absent. Given the number of county residents exposed to each type of fecal contamination, the estimated number of people ingesting these ARGs per day in their drinking water was 120, 420, and 80 for exposure to human, bovine, and both types of fecal source, respectively (out of 12,000 total private well users in the county). This work illustrates the relative impact of two different fecal sources on ARG exposure via drinking water for the study area and selected ARGs. Future work could be expanded to other settings and a more comprehensive suite of ARGs to understand the relative risks of exposure associated with each of AR’s human, agricultural, and environmental sectors.