Dynamics of SARS-CoV-2 in wastewater in three districts of the Buenos Aires metropolitan region, Argentina, throughout nine months of surveillance: A pilot study.

In the current pandemic of COVID-19, sewage surveillance of SARS-CoV-2 genome has been used to complement viral epidemiology in different countries. The aim of this work was to introduce and evaluate this wastewater-based tool in the metropolitan region of Buenos Aires, Argentina. As a pilot study, surveillance of SARS-CoV-2 in wastewater from three districts of this area was performed for more than nine months from June 2020 to April 2021. Viruses present in the samples were concentrated using polyethylene glycol precipitation and quantified using RT-qPCR CDC N1 assay. Virus recovery for SARS-CoV-2 and a potential surrogate, bovine coronavirus Mebus strain, that shares the Betacoronavirus genus and structural characteristics with SARS-CoV-2, were evaluated after concentration and detection procedures. Recovery of both viruses did not differ significantly, with a median for SARS-CoV-2 and BCoV of 0.085 (95% CI: 0.021-0.179) and 0.262 (95% CI: 1.18 × 10-5-0.564) respectively. The concentration of SARS-CoV-2 genome in wastewater ranged from 10 -1 to 10 3 cg/ml, depending on the wastewater treatment plant, type of collection site, viral recovery of the concentration method and the epidemiological situation of the outbreaks. Significant correlations were observed between SARS-CoV-2 concentration in wastewater and reported clinical cases, reinforcing the utility of this approach to monitor the epidemiological status of populations.

A rapid and simple protocol for concentration of SARS-CoV-2 from sewage.

The aim of this study was to set up a simple protocol to concentrate SARS-CoV-2 from sewage, which can be implemented in laboratories with minimal equipment resources. The method avoids the need for extensive purification steps and reduces the concentration of potential inhibitors of RT-qPCR contained in sewage. The concentration method consists of a single step, in which a small volume (40 mL) of sewage sample is incubated with polyaluminum chloride (PAC)(0.00045 N Al3+ final concentration). Virus particles adsorbed to the precipitate are collected by low-speed centrifugation, after which the recovered pellet is resuspended with a saline buffer. PAC-concentrated samples are stable for at least one week at 4 °C. Therefore, they may be sent refrigerated to a diagnosis center for RNA extraction and RT-qPCR for SARS-CoV-2 RNA detection if the lab does not have such capabilities. The PAC concentration method produced an average shift of 4.5-units in quantification cycle (Cq) values compared to non-concentrated samples, indicating a 25-fold increase in detection sensitivity. The lower detection limit corresponded approximately to 100 viral copies per ml. Kappa index indicated substantial agreement between PAC and polyethylene glycol (PEG) precipitation protocols (k = 0.688, CI 0.457-0.919). This low-cost concentration protocol could be useful to aid in the monitoring of community circulation of SARS-CoV-2, especially in low- and middle-income countries, which do not have massive access to support from specialized labs for sewage surveillance.