SARS-CoV-2 shedding sources in wastewater and implications for wastewater-based epidemiology

Wastewater-based epidemiology (WBE) approach for COVID-19 surveillance is largely based on the assumption of SARS-CoV-2 RNA shedding into sewers by infected individuals. Recent studies found that SARS-CoV-2 RNA concentration in wastewater (C(RNA)) could not be accounted by the fecal shedding alone. This study aimed to determine potential major shedding sources based on literature data of C(RNA), along with the COVID-19 prevalence in the catchment area through a systematic literature review. Theoretical C(RNA) under a certain prevalence was estimated using Monte Carlo simulations, with eight scenarios accommodating feces alone, and both feces and sputum as shedding sources. With feces alone, none of the WBE data was in the confidence interval of theoretical C(RNA) estimated with the mean feces shedding magnitude and probability, and 63% of C(RNA) in WBE reports were higher than the maximum theoretical concentration. With both sputum and feces, 91% of the WBE data were below the simulated maximum C(RNA) in wastewater. The inclusion of sputum as a major shedding source led to more comparable theoretical C(RNA) to the literature WBE data. Sputum discharging behavior of patients also resulted in great fluctuations of C(RNA) under a certain prevalence. Thus, sputum is a potential critical shedding source for COVID-19 WBE surveillance.