SARS-CoV-2 Detection in Wastewater Samples via Digital Droplet Polymerase Chain Reaction

SARS-CoV-2, or COVID-19 is a type of coronavirus that infects humans. It was first discovered in 2019 in Wuhan, China and has since spread worldwide infecting more than 100 million people as of March 2021. Due to the speed at which the virus spreads, primarily through respiratory droplets, close monitoring is necessary to detect potential outbreaks. One of the avenues of sampling involves detection of viral RNA in wastewater, which is a fast and accurate way to determine SARS-CoV-2 levels in a community. Clinical evidence suggests that both asymptomatic and symptomatic people pass SARS-CoV-2 viral particles in their feces very early on in the infection process. Studies indicate that viral particles can be detected in wastewater days before any clinical signs and symptoms are detectable in a patient.This provides critical information to public health authorities to track outbreaks and intervene earlier to prevent further spread of the virus. NMU partnered with Michigan EGLE to measure SARS-CoV-2 viral RNA levels in Marquette’s wastewater. Samples were collected weekly from four lift stations and the City of Marquette’s wastewater treatment plant. The raw samples were concentrated, and RNA was extracted and then processed via Digital Droplet Polymerase Chain Reaction (ddPCR) as described in the Standard Operating Procedure (Rose, et al.)1. Digital Droplet PCR is a nucleic acid detection system that uses water-oil emulsion droplets to quantify nucleic acid levels. Unlike other PCR techniques, ddPCR partitions individually generated droplets containing nucleic acid to provide absolute quantification that is highly sensitive. The data that was collected was used to observe SARS-CoV-2 levels over a period of fifteen weeks. High levels of SARS-CoV-2 were detected during the weeks of November 17th and December 1st, especially at the Pine Street Lift Station, and there has been a general downward trend