SARS-CoV-2 RNA detection and persistence in wastewater samples: An experimental network for COVID-19 environmental surveillance in Padua, Veneto Region (NE Italy)

Background: Clinical detection of SARS-CoV-2 RNA in stools supports the idea ofwastewater-based epidemiology (WBE) as a precious tool for COVID-19 environmental surveillance. Successful detection of SARS-CoV-2 RNA in untreated wastewaters has been reported in several countries. This study investigated the presence and persistence of viral RNA in treated and untreated wastewaters in Padua, Italy. An urban experimental network of sampling sites was tested for prospective surveillance activities. Methods: Seven sampling sites (i.e. wastewater pumping stations, plant inlets and outlets) were selected from the two main municipalwastewater treatment plant systems. Eleven grab samples (9 untreated, 2 treated wastewaters) were collected on 2 dates. All samples were tested at t0 for SARS-CoV-2 RNA and t1= 24 h to investigate its persistence, at room temperature and under refrigerated conditions. Overall, 33 sub-samples were concentrated by ultrafiltration and tested for molecular detection of viral RNA with two RT-qPCR assays. Results: At t0, positivity for at least one RT-qPCR assay was achieved by 4/9 untreated wastewater samples and 2/2 tertiary treated samples. A minimum SARS-CoV-2 titer of 4.8-4.9 log10 gc/L was estimated. At t1, three refrigerated subsamples were positive as well. The two RT-qPCR assays showed differential sensitivity, with the N assay detecting 90% of successful amplifications. Conclusions: SARS-CoV-2 RNA was detected in untreated and treated wastewaters. Its persistence after 24 h was demonstrated in subsamples kept at 4 degrees C. Hospitalization data suggested an approximateWBE detection power of 1 COVID-19 case per 531 inhabitants. The possible role of WBE in COVID-19 environmental surveillance is strongly supported by our findings. WBE can also provide precious support in the decision-making process of restriction policies during the epidemic remission phase. Optimization and standardization of laboratory methods should be sought in the short term, so that results from different studies can be compared with reliability. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This study in Padua, Italy, detected the presence of SARS-CoV-2 RNA in treated and untreated wastewaters, with the virus showing persistence after 24 hours at 4°C. Hospitalization data suggested that wastewater-based epidemiology detection can identify approximately 1 COVID-19 case per 531 inhabitants. These findings strongly support the potential role of wastewater-based epidemiology in COVID-19 environmental surveillance.