Early-pandemic wastewater surveillance of SARS-CoV-2 in Southern Nevada: Methodology, occurrence, and incidence/prevalence considerations

• Published in: Water research X 2021-01, Vol.10, p.100086, Article 100086
• Main Authors: Gerrity, Daniel, Papp, Katerina, Stoker, Mitchell, Sims, Alan, Frehner, Wilbur
• Format: Article
• Language: English
• Subjects: COVID-19; Incidence; Prevalence; SARS-CoV-2; Sewage; Wastewater surveillance
• ISSN: 2589-9147; 2589-9147
• DOI: 10.1016/j.wroa.2020.100086

The World Health Organization (WHO) classified COVID-19 as a global pandemic, with the situation ultimately requiring unprecedented measures to mitigate the effects on public health and the global economy. Although SARS-CoV-2 (the virus responsible for COVID-19) is primarily respiratory in nature, multiple studies confirmed its genetic material could be detected in the feces of infected individuals, thereby highlighting sewage as a potential indicator of community incidence or prevalence. Numerous wastewater surveillance studies subsequently confirmed detection of SARS-CoV-2 RNA in wastewater and wastewater-associated solids/sludge. However, the methods employed in early studies vary widely so it is unclear whether differences in reported concentrations reflect true differences in epidemiological conditions, or are instead driven by methodological artifacts. The current study aimed to compare the performance of virus recovery and detection methods, detect and quantify SARS-CoV-2 genetic material in two Southern Nevada sewersheds from March–May 2020, and better understand the potential link between COVID-19 incidence/prevalence and wastewater concentrations of SARS-CoV-2 RNA. SARS-CoV-2 surrogate recovery (0.34%–55%) and equivalent sample volume (0.1 mL–1 L) differed between methods and target water matrices, ultimately impacting method sensitivity and reported concentrations. Composite sampling of influent and primary effluent resulted in a ∼10-fold increase in concentration relative to corresponding grab primary effluent samples, presumably highlighting diurnal variability in SARS-CoV-2 signal. Detection and quantification of four SARS-CoV-2 genetic markers (up to ∼106 gene copies per liter), along with ratios of SARS-CoV-2 to pepper mild mottle virus (PMMoV), exhibited comparability with public health data for two sewersheds in an early phase of the pandemic. Finally, a wastewater model informed by fecal shedding rates highlighted the potential significance of new cases (i.e., incidence rather than prevalence) when interpreting wastewater surveillance data. [Display omitted] •10X higher SARS-CoV-2 concentration in composite vs. early-morning grab samples.•SARS-CoV-2 signal appears to exhibit diurnal variability.•Coronavirus recovery ranged from 0.3 to 55% depending on sample processing approach.•Secondary concentration to increase equivalent sample volume may not be warranted.•SARS-CoV-2 RNA concentrations in wastewater fluctuated between 104-106 gc/L.