Assessing Urban Ditches for Tracking SARS-CoV-2 in Low Sanitation Areas in Southeastern Brazil

Several studies investigated the presence of SARS-CoV-2 in water samples and raw urban wastewater collected from urban sewage treatment plants (STPs) during the COVID-19 pandemic and correlated viral load and epidemiological data. However, limited information is available regarding the potential of urban ditches as sampling sites for epidemiological surveillance. This study aimed to detect SARS-CoV-2 RNA in urban ditches and evaluate its correlation with epidemiological data. A total of 168 samples were collected from January 2021 to February 2022 in three urban ditches and two STPs in the metropolitan region of Vitória, Espírito Santo (ES). Physicochemical and microbiological water quality parameters were analyzed, and SARS-CoV-2 RNA was detected using a TaqMan RT-qPCR system. SARS-CoV-2 was detected in 145/168 of the samples, with 87.2% (75/86) found in the urban ditches and 85.3% (70/82) in the STPs. The viral load in the three urban ditches ranged from 1.59 × 10⁴ to 2.56 × 10⁴ genome copies/litre (GC/L) while in the two STPs, it ranged from 7.79 × 10³ to 1.26 × 10⁴ GC/L. A moderate to strong positive correlation was observed between viral load and confirmed COVID-19 cases, particularly for samples collected from urban ditches (ditch 1, r = 0.58; ditch 2, r = 0.78; ditch 3, r = 0.86). The results indicate greater correlation of SARS-CoV-2 RNA concentration in ditches of low sanitation areas as compared with STPs, showing that ditches could be an important and equivalent sampling point for viral epidemiological studies.