Inclusion of Physical-Chemical Water Quality Measurements Can Improve Associations between SARS-CoV-2 RNA Levels in Wastewater and COVID-19 Cases within Smaller Sewersheds.
Measurements of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in wastewater can be used to understand the prevalence of COVID-19 cases within a community. Environmental conditions inclusive of physical-chemical water quality characteristics are known to impact wastewater SARS-CoV-2 signals, but they are rarely measured within the sewer infrastructure in areas upstream of wastewater treatment plants (WWTPs). The objectives of this study were to report on measurements of environmental parameters [flow and physical-chemical water quality (water temperature, pH, specific conductivity, dissolved oxygen, and turbidity)] upstream of a WWTP and to evaluate whether the inclusion of these environmental parameters improves correlations between SARS-CoV-2 RNA levels in wastewater, and COVID-19 prevalence in the sewershed community. Measurements of environmental parameters and SARS-CoV-2 RNA in wastewater spanned different time scales (minutes, hours and weeks) and population scales (building, campus, community). For short time scales, water quality parameters did not improve correlations between SARS-CoV-2 in wastewater and COVID-19 prevalence due to high variability of water quality and flows within the sewer system. When averaging data over weekly time scales, regressions showed that inclusion of pH improved correlations between RNA and COVID-19 prevalence. At the cluster scale, for the entire data set, the root mean square error decreased from 6.9 cases per week to 6.5 cases per week. At the community scale benefits were observed only for the delta wave with a decrease in root mean square error from 539 cases per week to 430 cases per week. The inclusion of pH improved correlations between wastewater SARS-CoV-2 and COVID-19 prevalence more frequently when evaluating the cluster sewershed scale (populations of a few thousand) in comparison to the community scale (populations of several 100,000). Given the simplicity of measuring pH and other physical-chemical water quality parameters, their inclusion should be considered as part of wastewater-based epidemiology programs.