This article, shows that it may be possible to monitor outbreaks of COVID-19 by monitoring the sewage of cities for viral particles.
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To quote this article in bibliography:
Kordatoua, Michael, P Karaoliaa, D Fatta-Kassinos. “Sewage analysis as a tool for the COVID-19 pandemic response and management: the urgent need for optimised protocols for SARS-CoV-2 detection and quantification." Journal of Environmental Chemical Engineering 8, no. 5 (2020): 1271-1283. https://doi.org/10.1016/j.jece.2020.104306