ABSTRACT
Wastewater-based epidemiology provides an approach for assessing the prevalence of pathogens such as COVID-19 in a sewer service area. In this study, SARS-CoV-2 RNA was measured serially in 44 wastewater treatment plants of varying service capacities comprising approximately 67% of the population of Minnesota, from September 2020 through December 2022. We employed linear regression models to establish a predictive relationship between the weekly SARS-CoV-2 RNA concentrations in wastewater and clinical case counts. Metrics were assessed under specified transformation and normalization methods which we confirmed by cross-validation averaged across the enrolled treatment plants. We report that the relationship between COVID-19 incidence and SARS-CoV-2 RNA in wastewater may be treatment plant-specific. Toward establishing guidelines for pathogen surveillance, we further studied storage and time-to-analysis for RNA wastewater data and observed large effects of storage temperature, indicating that collection methods may have an important effect on the utility and validity of wastewater data for infectious disease monitoring. Our findings are additive for any large-scale wastewater surveillance program.