No evidence for environmental transmission risk of SARS-CoV-2 in the UK’s largest urban river system: London as a case study

The presence of SARS-CoV-2 in untreated sewage has been confirmed in many countries but its incidence and infection risk in contaminated freshwaters is still poorly understood. The River Thames in the UK receives untreated sewage from 57 Combined Sewer Overflows (CSOs), with many discharging dozens of times per year. We investigated if such discharges provide a pathway for environmental transmission of SARS-CoV-2. Samples of wastewater, surface water, and sediment collected close to six CSOs on the River Thames were assayed over 8 months for SARS-CoV-2 RNA and infectious virus. Bivalves were sampled as sentinel species of viral bioaccumulation. Sediment and water samples from the Danube and Sava rivers in Serbia, where raw sewage is also discharged in high volumes, were assayed as a positive control. We found no evidence of SARS-CoV-2 RNA or infectious virus in UK samples, in contrast to RNA positive water and sediment samples from Serbia. Furthermore, we show that infectious SARS-CoV-2 inoculum is stable in Thames water and sediment for < 3 days, while RNA remained detectable for at least seven days. This indicates that dilution of wastewater likely limits environmental transmission, and that infectivity should be embedded in future risk assessments of pathogen spillover.