Enumerating asymptomatic COVID-19 cases and estimating SARS-CoV-2 fecal shedding rates via wastewater-based epidemiology

Schmitz, B. W.; Innes, G. K.; Prasek, S. M.; Betancourt, W. Q.; Stark, E. R.; Foster, A. R.; Abraham, A. G.; Gerba, C. P.; Pepper, I. L.

Wastewater-based epidemiology (WBE) was utilized to monitor SARS-CoV-2 RNA in sewage collected from manholes specific to individual student dormitories (dorms) at the University of Arizona in the fall semester of 2020, which led to successful identification and reduction of transmission events. Positive wastewater samples triggered clinical testing of almost all residents within that dorm; thus, SARS-CoV-2 infected individuals were identified regardless of symptom expression. This current study examined clinical testing data to determine the abundance of asymptomatic versus symptomatic cases in these defined communities. Nasal and nasopharyngeal swab samples processed via antigen and PCR tests indicated that 79.2% of SARS-CoV-2 infections were asymptomatic, and only 20.8% of positive cases reported COVID-19 symptoms at the time of testing. Clinical data was paired with corresponding wastewater virus concentrations, which enabled calculation of viral shedding rates in feces per infected person(s). Mean shedding rates averaged from positive wastewater samples across all dorms were 6.84 {+/-} 0.77 log10 genome copies per gram of feces (gc/g-feces) based on the N1 gene and 7.74 {+/-} 0.53 log10 gc/g-feces based on the N2 gene. Quantification of SARS-CoV-2 fecal shedding rates from infected persons has been the critical missing component necessary for WBE models to measure and predict SARS-CoV-2 infection prevalence in communities. The findings from this study can be utilized to create models that can be used to inform public health prevention and response actions.