Sars-CoV2 in wastewater: 2021-2023 surveillance in three provinces of Lombardia region (Italy)

BACKGROUND: Sars-CoV2 pandemic has shown the importance of wastewater surveillance to monitor virus diffusion and its environmental permanence; WHO experts highlighted the importance of wastewater controls as early detection system to individuate Sars-CoV2 and other viruses which could potentially spread to the population. The aim of this work was to investigate the presence of Sars-CoV2 in wastewater from Brescia, Cremona and Bergamo cities during 2021-2023 years after pandemic event. METHODS: From the end of 2021 until now, 341 wastewater samples were collected and analyzed at Food Control department to detect Sars-CoV2. After the inactivation at 56 °C for 30 minutes, samples were centrifugated and extracted by eGENE-UP® system (bioMérieux). Virus detection was based on three genes amplification: ORF, N1 and N3. Quantification in genome copies/µL (cg/µL) was performed. RESULTS: Almost all samples were positive for virus presence; in particular ORF gene was detected in 94% of samples (IC95% 91,6 - 96,7%); the other genes N1 and N3 were detected respectively in 91% (IC95% 87,2 - 93,6) and 98% (IC95% 95 - 99%). In only three samples all genes simultaneously were not detected. ORF and N1 were quantified between 103 and 104 cg/µL without differences among seasons. N3 was quantified at higher values than the other genes (104 in 57% of samples; IC95% 51,4 - 62,2%). CONCLUSIONS: The pandemic has run out with the safety measures applied, but wastewater surveillance has highlighted virus circulation, even if at lower, constant levels than in pandemic period. Virus quantity in wastewater followed and sometime preceded epidemic trend. Wastewater control could support competent authorities in epidemic event management. Environmental surveillance, as already demonstrated during pandemic period, could represent an alert system for Sars-Cov2 and oral fecal route virus spreading KEY MESSAGES: • Wastewater surveillance is an important tool to control Sars-CoV2 mutation and spreading. • Environmental viruses’ surveillance can support competent authorities in decisions regarding public health.