SARS-CoV-2 RNA in urban wastewater samples to monitor the COVID-19 epidemic in Lombardy, Italy (March - June 2020)

Castiglioni, S.; Schiarea, S.; Pellegrinelli, L.; Primache, V.; Galli, C.; Bubba, L.; Mancinelli, F.; Marinelli, M.; Cereda, D.; Ammoni, E.; Pariani, E.; Zuccato, E.; Binda, S.

Wastewater-based viral surveillance is a promising approach to monitor the circulation of SARS-CoV-2 in the general population. The aim of this study was to develop an analytical method to detect SARS-CoV-2 RNA in urban wastewater, to be implemented in the framework of a surveillance network in the Lombardy region (Northern Italy). This area was the first hotspot of COVID-19 in Europe. Composite 24h samples were collected weekly in eight cities from end-March to mid-June 2020 (first peak of the epidemic). The method developed and optimized, involved virus concentration, using PEG centrifugation, and one-step real-time RT-PCR for analysis. SARS-CoV-2 RNA was identified in 65 (61%) out of 107 samples, and the viral concentrations (up to 2.1 E +05 copies/L) were highest in March-April. By mid-June, wastewater samples tested negative in all the cities. Viral loads were used for inter- city comparison and Brembate, Ranica and Lodi had the highest. The pattern of decrease of SARS-CoV-2 in wastewater was closely comparable to the decline of active COVID-19 cases in the population, reflecting the effect of lock-down. Wastewater surveillance of SARS-CoV-2 can integrate ongoing virological surveillance of COVID-19, providing information from both symptomatic and asymptomatic individuals, and monitoring the effect of health interventions.