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Tracking community infection dynamics of COVID-19 by monitoring SARS-CoV-2 RNA in wastewater, counting positive reactions by qPCR

Wastewater-based epidemiology has proved useful for monitoring the COVID-19 infection dynamics in communities. However, in some countries, low concentrations of SARS-CoV-2 RNA in wastewater make this difficult. Getting meaningful information from wastewater-based epidemiology in regions of low prevalence remains a key challenge. Here we used real-time reverse-transcription PCR (RT-qPCR) to monitor SARS-CoV-2 RNA in wastewater from October 2020 to February 2021 during the third wave of the COVID-19 outbreak in Japan. Viral RNA was below the limit of quantification in all samples. However, by counting the positive reactions in repeated qPCR of each sample, we found that the ratio of positive reactions to all tests in wastewater was significantly correlated with the number of clinically confirmed cases by the date of symptom onset during periods of both increasing and decreasing infection. Time-step analysis indicated that COVID-19 patients excreted large amounts of virus in their feces 2 days either side of symptom onset, which wastewater surveillance could detect. The positive count method is thus useful for tracing COVID-19 dynamics in regions of low prevalence.