A comprehensive one-year correlation analysis between prevalence and number of sars-cov-2 rna copies detected in wastewater from 8 sicilian cities in italy

Background and objectives: Several authors have reported positive correlations between wastewater SARS-CoV-2 concentrations and the community’s burden of infection, providing information about the disease’s epidemiological trend. This pre-post study evaluated – within a year of active surveillance, from October 1st,2021, to September 30th, 2022 – the relation between daily SARSCoV-2 prevalence and the number of genome copies/L detected in West Sicily wastewater samples. This study is part of a national framework coordinated by Istituto Superiore di Sanità. Methods: Quantitative data from analysing 486 wastewater samples collected from 9 purification plants in 8 Sicilian cities (Agrigento, Bagheria, Caltanissetta, Enna, Marsala, Mazara del Vallo, Palermo, and Trapani) were obtained. Correlation and logistic regression analysis were performed between the communal-based aggregated prevalence of daily SARS-CoV-2 cases obtained from the integrated national surveillance system and the number of genomic copies/L derived from wastewater analysis for different times (day-prevalence t0, t7, t14) and different periods (0- to 6-, 6- to 12- and comprehensive 12 months). Results: A moderate-high correlation index was retrieved for 0- to 6- months (October 2021–March 2022, t0: r=0.75, R2=0.57; t7 r=0.76, R2=0.58, t14 r=0.76, R2=0.58) and overall analyses (October 2021–October 2022, t0 r=0.63, R2=0.40; t7 r=0.62, R2=0.38; t14 r=0.59, R2=0.35). On the other hand, 6- to 12- months analysis displayed a relevant decline in correlation (March 2022–October 2022, t0 r=0.19, R2=0.04; t7 r=0.17, R2=0.03, p=0.004; t14 r=0.11, R2=0.01). All data except t14 were statistically significant (p<0.0001). Conclusions: Significance results were displayed for 0- to 6- and overall analysis at 0,7 and 14 days. Despite 6- to 12- months samples tested positive for RNA copies, a progressive loss of significance was found probably mainly attributable to a progressive loss of function in prevalence estimation of the swab-related SARSCoV-2 positivity detecting system due to underreporting of cases.