No abstract

COVID‐19 wastewater‐based epidemiology has been performed in catchments of various sizes and sewer types with many short‐term studies available and multi‐seasonal studies emerging. The objective of this study was to compare weekly observations of SARS‐CoV‐2 genes in municipal wastewater across multiple seasons for different systems as a factor of sewer type (combined, separate sanitary) and system size. Sampling occurred following the first wave of SARS‐CoV‐2 cases in the study region (June 2020) and continued through the third wave (May 2021), the period during which clinical testing was widely available and different variants dominated clinical cases. The strongest correlations were observed between wastewater N1 concentrations and the cumulative clinical cases reported in the 2 weeks prior to wastewater sampling, followed by the week prior, new cases, and the week after wastewater sampling. Sewer type and size did not necessarily explain the strength of the correlations, indicating that other non‐sewer factors may be impacting the observations. In‐system sampling results for the largest system sampled are presented for 1 month. Removing wet weather days from the data sets improved even the flow‐normalized correlations for the systems, potentially indicating that interpreting results during wet weather events may be more complicated than simply accounting for dilution. Practitioner Points SARS‐CoV‐2 in wastewater correlated best with total clinical cases reported in 2 weeks before wastewater sampling at the utility level. Study performed when clinical testing was widespread during the year after the first COVID‐19 wave in the region. Sewer type and size did not necessarily explain correlation strength between clinical cases and wastewater‐based epidemiology results. Removing wet weather days improved correlations for 3/4 utilities studied, including both separate sanitary and combined sewers.

Wastewater-based epidemiology is a useful tool to track COVID-19 community infections. While recommendations exist for normalizing wastewater virus concentrations to the flow and number of people in the sewershed, less information is available regarding the potential for in-sewer processes to impact these observations. The aim of this research was to evaluate SARS-CoV-2 accumulation in simulated sewer biofilms. An annular biofilm reactor was continuously fed with raw wastewater from a separate sanitary sewer during periods of high and low COVID-19 incidence. Periodic biofilm samples were collected, and SARS-CoV-2 and pepper mottle virus gene copies were quantified via RT-qPCR. During the period of low COVID-19 incidence, SARS-CoV-2 was below detection or below the quantitation limit in the sewer biofilms. During the period of high COVID-19 incidence, SARS-CoV-2 gene copies increased in the sewer biofilm across the 4-week study period. Accumulation of ∼700 genome copies/cm2 was observed in the biofilm and correlated with cumulative cases in the county. During both study periods, the pepper mottle virus plateaued after 1 week. These results provide insight into the potential for SARS-CoV-2 retardation in sewer biofilms, which may be of interest for interpreting wastewater-based epidemiology data, protecting utility workers, and monitoring infections.