Long-term longitudinal monitoring of SARS CoV-2 in urban rivers and sewers of Nepal

In regions without adequate centralized wastewater treatment plants, sample collection from rivers and sewers can be an alternative sampling strategy for wastewater surveillance. This study aimed to assess the feasibility of alternative sampling strategies by testing samples collected from rivers (n = 246) and sewers (n = 244) in the Kathmandu Valley between March 2021 and February 2022. All samples were concentrated using the skimmed-milk flocculation method and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA was quantified using the nucleocapsid (N) and envelope (E) genes qPCR assays. Of the total, 75 % (371/490) of the samples tested positive using at least one qPCR assay, with concentrations ranging from 3.0 to 8.3 log10 gene copies/L. No significant correlation between concentrations of SARS-CoV-2 from both sewers and river with the number of confirmed coronavirus disease 2019 (COVID-19) cases in the Kathmandu valley was observed (p > 0.05). Despite the high concentration of SARS-CoV-2 in rivers and sewers, we hypothesize this finding to be a result of inaccurate number of clinical cases possibly due to inadequate clinical testing. This longitudinal study further supports the statement to consider sampling strategies from sewers and rivers for WBS in Nepal and other low and middle-income countries. [Display omitted] •Wastewater-based surveillance was conducted via sampling from sewers and river.•SARS-CoV-2 was detected in 75 % of the total samples collected.•No significant correlation between SARS-CoV-2 concentration and COVID-19 cases.•Rivers and sewers are alternative sampling sources for WBS.