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

Wehrendt, D. P.; Masso, M. G.; Gonzales Machuca, A.; Vargas, C. V.; Barrios, M. E.; Campos, J.; Costamagna, D.; Bruzzone, L.; Cisterna, D. M.; Iglesias, N. G.; Mbayed, V. A.; Baumeister, E.; Centron, D.; Quiroga, M. P.; Erijman, L.

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 of sewage sample is incubated with polyaluminum chloride (PAC). Virus particles adsorbed to the precipitate are collected by low-speed centrifugation, after which the recovered pellet is resuspended with a saline buffer. The PAC concentration method produced an average shift of 4.4-units in Cq values compared to non-concentrated samples, indicating a 25-fold increase in detection sensitivity. The lower detection limit corresponded approximately to 100 copies per ml. Kappa index indicated substantial agreement between PAC and PEG precipitation protocols (k=0.688, CI 0.457-0.919). PAC concentrated samples can be processed immediately for RNA purification and qPCR or sent refrigerated to a diagnosis center, where SARS-CoV-2 detection should be performed in the same way as for clinical samples. This low cost 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.