Wastewater surveillance of SARS-CoV-2 corroborates heightened community infection during the initial peak of COVID-19 in Bexar County, Texas

Abstract

The purpose of this study was to conduct a preliminary assessment of the levels of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in wastewater at the Salitrillo Wastewater Treatment Plant in Texas during the initial peak of coronavirus disease 2019 (COVID-19) outbreak. Raw wastewater influent (24 h composite, time-based 1 L samples, <i>n</i> = 13) was collected weekly during June-August 2020. We measured SARS-CoV-2 RNA in wastewater by reverse transcription droplet digital PCR using the same N1 and N2 primer sets as employed in COVID-19 clinical testing. Virus RNA copies for positive samples (77%) ranged from 1.4 × 10² to 4.1 × 10⁴ copies per liter of wastewater, and exhibited both increasing and decreasing trends, which corresponded well with the COVID-19 weekly infection rate (N1: ρ = 0.558, <i>P</i> = 0.048; N2: ρ = 0.487, <i>P</i> = 0.092). A sharp increase in virus RNA concentrations was observed during July sampling dates, consistent with the highest number of COVID-19 cases reported. This could be attributed to an increase in the spread of COVID-19 infection due to the Fourth of July holiday week gatherings (outdoor gatherings were limited to 100 people during that time). Our data show that wastewater surveillance is an effective tool to determine trends in infectious disease prevalence, and provide complementary information to clinical testing.