ABSTRACT
To investigate whether wastewater surveillance can be used as an early warning system to detect a rise in SARS-CoV-2 positive cases, and to follow the circulation of specific variants of concern (VOC) in particular geographical areas, wastewater samples were collected from local neighborhood sewers and from a large regional wastewater treatment plant (WWTP) in the area of Leuven, Belgium. In two residential sampling sites, a rise in viral SARS-CoV-2 copies in wastewater preceded the peaks in positive cases. In the WWTP, peaks in the wastewater viral load were seen simultaneous with the waves op positive cases caused by the original Wuhan SARS-CoV-2 strain, the Alpha variant and the Delta variant. For the Omicron BA.1 variant associated wave, the viral load in wastewater increased to a lesser degree, and much later than the increase in positive cases, which could be attributed to a lower level of fecal excretion, as measured in hospitalized patients. Circulation of SARS-CoV-2 VOCs (Alpha, Delta and Omicron) could be detected based on the presence of specific key mutations. The shift in variants was noticeable in the wastewater, with key mutations of two different variants being present simultaneously during the transition period. We found that wastewater based surveillance is a sensitive tool to monitor SARS-CoV-2 circulation levels and VOCs in larger regions. This can prove to be highly valuable in times of reducing testing capacity. Differences in excretion levels of various SARS-CoV-2 variants should however be taken into account when using wastewater surveillance to monitor SARS-CoV-2 circulation levels in the population.
