Modeling SARS-CoV-2 RNA Degradation in Small and Large Sewersheds

Wastewater-based epidemiology has been at the forefront of the COVID-19 pandemic, yet little is known about losses of SARS-CoV-2 in sewer networks. Here, we used advanced sewershed modeling software to simulate SARS-CoV-2 RNA loss in sewersheds across Houston, TX under various temperatures and decay rates. Moreover, a novel metric, population times travel time (PT), was proposed to identify localities with a greater likelihood of undetected COVID-19 outbreaks and to aid in the placement of upstream samplers. Findings suggest that travel time has a greater influence on viral loss across the sewershed as compared to temperature. SARS-CoV-2 viral loss at median travel times was approximately two times greater in 20 degrees Celsius wastewater between the small sewershed, Chocolate Bayou, and the larger sewershed, 69th Street. Lastly, placement of upstream samplers according to the PT metric can provide a more representative snapshot of disease incidence in large sewersheds. This study helps to elucidate discrepancies between SARS-CoV-2 viral load in wastewater and clinical incidence of COVID-19. Incorporating travel time and SARS-CoV-2 decay can improve wastewater surveillance efforts.