An integrative analysis of SARS-CoV 2 during the first and second waves of COVID-19 in Salta, Argentina

Wastewater surveillance has been extensively applied to provide information about SARS-CoV-2 circulation in the community. However, its applicability is limited in regions lacking adequate sewerage infrastructure, without wastewater treatment plants (WWTP) or with insufficient coverage. During the COVID-19 pandemic, from July 2020 to September 2021, comprehensive epidemiological data encompassing positive, recovered, and deceased cases were collected alongside precipitation records. Additionally, wastewater samples from 13 main sewersheds and river water from two points (up- and downstream the main WWTP), in the city of Salta, were gathered. A total of 452 water samples were analyzed for quantitative detection of SARS-CoV-2 using reverse transcription real-time PCR. Across the 62-week study period, two distinct waves of COVID-19 were identified. The dynamics of deceased cases showed peaks 10 and 28 days after the peaks of positive cases in the first and second waves, respectively. Downstream river water exhibited higher fecal contamination than the upstream samples, evincing the impact of the WWTP discharges. Viral concentration in river waters mirrored those from wastewater, reflecting the progression of cases. Despite the lower reported number of cases during the first wave in comparison to the second (5420 vs. 8516 cases at the respective peaks), higher viral concentrations were detected in water samples (1.97 × 10⁷ vs. 2.36 × 10⁶ gc/L, respectively), suggesting underreporting during the first wave, and highlighting the positive effect of vaccination during the second. To the best of our knowledge, this is the first study that simultaneously and systematically analyzed surface water and wastewater over a prolonged period, the effect of precipitations were considered for the variations in the concentrations, and the findings compared with epidemiological information. Environmental surveillance was demonstrated to be a great tool to obtain valuable information about the circulation patterns of SARS-CoV-2, especially under resource constraints to massively test the population, thus, underreporting cases. Furthermore, the methodology employed herein can be easily expanded to the community-level surveillance of other pathogens excreted in urine and feces, encompassing viruses, bacteria, and protozoa.