Multidimensional Analysis of SARS-CoV-2 RNA in Nine Sites Located in Campania Region, Italy

Wastewater monitoring has been recognized as a valid tool for monitoring coronavirus disease 2019 (COVID-19) diffusion. In this paper we analyse a dataset composed by the measurements of SARS-CoV-2 RNA load in 605 raw wastewater samples collected from nine wastewater treatment plants (WWTPs) in the Campania region from October 2021 to May 2025. We analyse the correlation structure of the dataset using multivariate statistical techniques with the aim of identifying the most representative sentinel WWTPs and thus optimizing the number of samples. Results of spatial analysis showed that there are two isolated elements, SA3 and NA1, with the highest and lowest SARS-CoV-2 load values, respectively, and other two clusters (Cl1 and Cl2) from the other WWTPs. Temporal analysis showed that NA3 WWTP had a statistically significant difference in SARS-CoV-2 load from 2022 to 2023. Our method suggests limiting samplings to three sites, as follows: SA3 (which can act as a sentinel site because it is the first site that records variation in viral load) and two with the higher variation coefficients (CV%) belonging to the two clusters, as follows: CE1 for Cl1 and NA4 for Cl2. This data analysis procedure could allow to focus only on certain WWTPs for SARS-CoV-2 monitoring, to promptly identify outbreaks.