The purpose of this study was to conduct a correlative assessment of SARS-CoV-2 RNA
concentrations in wastewater with COVID-19 cases and a systematic evaluation of the
effect of using different virus concentration methods and recovery and normalization
approaches. We measured SARS-CoV-2 RNA concentrations at two different wastewater
treatment plants (WWTPs) in the Bexar County of Texas from October 2020 to May 2021 (32
weeks) using reverse transcription droplet digital PCR (RT-ddPCR). We evaluated three
different adsorption–extraction (AE) based virus concentration methods
(acidification, addition of MgCl
2
, or without any pretreatment) using bovine
coronavirus (BCoV) as surrogate virus and observed that the direct AE method showed the
highest mean recovery. COVID-19 cases were correlated significantly with SARS-CoV-2 N1
concentrations in Salitrillo (ρ = 0.75,
p
< 0.001) and
Martinez II (ρ = 0.68,
p
< 0.001) WWTPs, but normalizing to a
spiked recovery control (BCoV) or a fecal marker (HF183) reduced correlations for both
treatment plants. The results generated in this 32-week monitoring study will enable
researchers to prioritize the virus recovery method and subsequent correlation studies
for wastewater surveillance.
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