Wastewater Provides Information on the R-Value of SARS-CoV-2

The effective reproductive number (R-value) of a virus indicates how many people on average are infected by a person, and thus represents the transmission speed of a disease. The R-value is widely used during the COVID-19 pandemic to track disease dynamics, inform regional and national policies, and estimate the effectiveness of interventions. So far, the R-value has been estimated based on clinical data, in particular observed cases, hospitalizations, and/or deaths.

Jana S. Huisman, ETH Zurich, Swiss Federal Institute of Technology, Basel, Switzerland, and colleagues have shown that the R-value can be reliably estimated by measuring the dynamics of SARS-CoV-2 RNA in wastewater in near real-time and independent of clinical data. The method is robust and applicable to data from different countries and wastewater matrices.

Infected people pass the virus into the sewage system, for example, when brushing their teeth or on the toilet. The virus concentration in the wastewater varies depending on how many people are sick at a certain point in time. The researchers determine the viral load in the wastewater using a test that works similarly to the PCR tests in humans. The team has developed a mathematical model to derive how many people are infected by the virus.

The technique was tested in Zurich and San Jose, CA, USA, and has proven to be reliable. The team found that estimates for the R-value that are similar to those obtained with clinical data result if the wastewater is analyzed at least three times a week. The technology thus allows a quick and inexpensive assessment of the epidemiological situation. In addition, the technology enables regular analyzes when clinical tests are rarely carried out at one location. The approach could thus be used to monitor pathogens other than Sars-Cov-2 for which no clinical data are available, e.g., for other human coronaviruses, enteroviruses, noroviruses, rotaviruses, or even for influenza.

Wastewater-based estimation of the effective reproductive number of SARS-CoV-2,
Jana S. Huisman, Jérémie Scire, Lea Caduff, Xavier Fernandez-Cassi, Pravin Ganesanandamoorthy, Anina Kull, Andreas Scheidegger, Elyse Stachler, Alexandria B. Boehm, Bridgette Hughes, Alisha Knudson, Aaron Topol, Krista R. Wigginton, Marlene K. Wolfe, Tamar Kohn, Christoph Ort, Tanja Stadler, Timothy R. Julian,
medRxiv 2021.
https://doi.org/10.1101/2021.04.29.21255961

The research has been published as a preprint and has not yet been peer-reviewed.

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