Applications of Wastewater-Based Surveillance Within Rural and Unsewered Communities

Abstract

Wastewater-based surveillance (WBS) presents the opportunity to describe disease and health trends within human populations both more broadly and at a lower cost than clinical reporting. However, rural communities and 'unsewered' households, the latter of which typically treat household wastewater onsite via septic system, remain a barrier to obtaining data that is truly representative of the population. The degree to which resulting data gaps impact WBS datasets has not been explored. Furthermore, these communities, especially when associated with socioeconomic barriers, can be more vulnerable than the general population to the impacts and circulation of infectious disease and antimicrobial resistance (AMR); this makes them key communities for surveillance and intervention. The goal of this research was to explore existing gaps in rural wastewater coverage in surveillance efforts within the context of AMR. This effort aimed both to systematically characterize prior AMR WBS literature for rural and onsite systems and to examine the occurrence of antibiotic resistance genes (ARGs) within septic systems compared with 'standard' untreated sewage collected at the intake to centralized wastewater treatment plants. Review of the existing literature confirmed that rural, small, and onsite wastewater systems were targets for only a small fraction of WBS campaigns, rendering a meta-analysis of their derived data infeasible. Highly recommended WBS techniques, such as longitudinal sampling campaigns or metagenomic sequencing, were particularly rare for rural applications, suggesting a potential gap in the generalizability of data derived from those techniques. Notably, conventional septic systems, which treat the waste of more than a fifth of the U.S. population, were included in only a handful of prior studies targeting AMR. It should be noted that WBS can be integrated with 'treated effluent' sampling for the purposes of environmental surveillance and risk assessment, which are considered key in the surveillance of AMR given its ability to persist and proliferate in natural settings. Given the reliance of septic systems on environmental systems for final treatment and their association with private drinking water resources, this oversight suggests an area of need for research into potential environmental pathways contributing to AMR spread. Septage (a pumpout of the septic tank contents) and septic tank effluent yielded consistent detection rates of ARGs and comparable ARG concentrations when compared with untreated centralized sewage from similar regions. This suggests, in accordance with the limited prior research, that targeted WBS campaigns including septic systems are feasible. Intriguingly, this also suggests that attenuation of some ARGs in the tank may be limited. However, there were noteworthy differences between the matrices, including a lower abundance of blaCTX-M and higher abundance of intI1 within septage and septic effluent samples compared with sewage; the former represents a gene encoding resistance to clinically-important beta lactam antibiotics and the latter acts as an indicator of multi-antibiotic resistance and propensity to mobilize to new bacterial hosts. However, the general similarity may suggest that centralized sewer collection may sufficiently capture unsewered population health in in some cases.