Sewage surveillance of the new SARS-CoV-2 virus, also referred to as Wastewater-based Epidemiology (WBE), has started to be utilized as a tool to support clinical epidemiology and for the overall understanding of disease spread. Weekly wastewater samples were collected from two treatment plants in San Antonio, Texas. Collection from Salitrillo WWTP started in June 2020, close to the highest peak of the crisis, while collection from Martinez WWTP started in October 2020. Samples were processed and analyzed for a set of SARS-CoV-2-specific primers and probes, using Reverse Transcription-Droplet Digital Polymerase Chain Reaction (RT-ddPCR). The quantitative data on SARS-CoV-2 prevalence was reported out in viral RNA copies per volume of wastewater for the specific treatment service area. This allowed for the direct comparison of SARS-CoV-2 genetic trace levels in different time periods where high detections are anticipated (holidays period), as well as comparison between WBE virus levels and number of reported clinical cases. Results of the RT-ddPCR based gene analysis indicated the presence of SARS-CoV-2 genetic traces in the Salitrillo WWTP samples with average RNA concentrations between 5.0 x 102 and 4.1 x 104 (copies L-1 WW). The same analysis also showed an increasing and decreasing trends with a maximum of 9.0 x 104 (copies L-1 WW) viral concentration in Martinez WWTP samples. On average, an increase in the concentration of viral RNA was observed which correlates well with an increase in the number of cases in the catchment area. Our findings demonstrated that wastewater surveillance is an effective tool to support clinical data in establishing trends of infectious disease prevalence.
