Chapter 10 - Viral surveillance of wastewater as a promising tool to assess the spread of pathogens in the population: the experience of SARS-CoV-2

Abstract

Wastewater-based epidemiology (WBE) is an innovative methodology enabling the retrieval of epidemiological information from untreated urban wastewater, and it is a very promising tool to timely monitor the circulation of viruses and to characterize viral strains as previously demonstrated for polioviruses and nonpolio-enteroviruses. At the beginning of the COVID-19 pandemic WBE was assessed as a complementary surveillance tool for monitoring the spread of SARS-CoV-2 in the population. The aim of this study was to evaluate whether WBE can be used as an early warning system to detect the presence of pathogens, and as a complementary tool to monitor the spread of epidemic and tracking changes in real time. Several cities were monitored for SARS-CoV-2 throughout 2020 and 2021 in Lombardy (Northern Italy), the most COVID-19 affected area in Italy. A direct correlation between the viral loads found in wastewater and other epidemiological data from clinical assessment was observed in all the investigated cities. In Milan, while the data were consistent among the first three waves, a divergence was observed during the fourth one. The wastewater viral load increased while the number of SARS-CoV-2-positive cases and hospitalizations remained stable, uncovering the effectiveness of the COVID-19 vaccines. Thus, wastewater surveillance by WBE may complement data from clinical surveillance, even overcoming it if applied for assessing the real spread of new pathogen(s) threatening human health that can be biased by the application of different clinical surveillance strategies.