Wastewater disease surveillance in distinct urban sewershed scales, Louisville, KY

The role of wastewater disease surveillance at distinct urban sewershed scales has been underresearched. The aim of this work was to investigate the presence and variability of SARS-COV-2 across 17 sewersheds in Louisville, KY, USA, across a range of population sizes, geographic areas and locations within the sewer network. The study period was August 2020 to April 2021, prior to the B.1.617.2 virus. A review of the sewer network service area found that 97% of households were included in our wastewater disease surveillance, indicating equity in our community monitoring in approach. The study results indicate in-network community sample locations from manhole street lines, and which are closer to the deposition of feces of COVID-19 infected patients, had the widest variability of median values of the loge concentration SARS-COV-2. The five treatment centers, sampling from 31,000 to 350,000 people had fewer extreme values likely because of mixing. In a study area of 770,000 people, the sewershed site-specific loge concentrations do not have the same temporal trends and even neighboring geographic areas did not necessarily have correlations, demonstrating the utility of studying sub-populations down to 8,000 people for public health response which is lost if only performing wastewater disease surveillance at treatment centers. Pertinently, larger catchment areas (<100,000) are less sensitive to changes in SARS-CoV-2 in the population when compare with sub 100,000 person catchment areas. The results of this study may inform other systems wide strategies in wastewater disease surveillance beyond SARS-CoV-2 targets.