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
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University of Palermo Department of Health Promotion, Mother and Child Care, Internal Medicine, and Medical Specialties "G. D'Alessandro" (PROMISE) Via del Vespro, 133, 90127 Palermo Italy
Istituto Zooprofilattico Sperimentale della Sicilia Area diagnostica virologica Via Gino Marinuzzi, 3, 90129 Palermo Italy
University Hospital "P. Giaccone." Clinical Epidemiology Unit and Regional Reference Laboratory of Western Sicily for the Emergence of COVID-19 Via del Vespro 133, 90127 Palermo Italy
Publication date: 2023-04-26
Popul. Med. 2023;5(Supplement):A1876
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 SARS-CoV-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.

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).

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).

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 SARS-CoV-2 positivity detecting system due to underreporting of cases.

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