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Sewage monitoring estimates the number of Yosemite visitors infected with the coronavirus

  • Sewage monitoring estimates the number of Yosemite visitors infected with the coronavirus

Wastewater testing shows visitors to Yosemite National Park in California may have had COVID-19, even though individual testing at the park’s medical clinic has not found any positive cases, reports The Guardian.

Dr Eric Sergienko, health official at Mariposa county, home of Yosemite, thought wastewater testing could be a good idea: “we really did not have a really good way of monitoring our visitors for COVID-19.” Untreated wastewater samples have been sent to Biobot Analytics for testing. The findings show an estimated 170 infected people in the park the week of the 4th of July, dropping to 60 the week after.

Mariposa county will continue to monitor sewage weekly, while adhering to safety protocols. Yosemite was closed for almost three months when the pandemic began; it has since reopened but the number of visitors is restricted to only about half the number in June of last year. Visitor centres are closed for the summer of 2020. National parks are under federal jurisdiction and hence wearing masks can be recommended but is not mandatory for staff or visitors, according to the National Park Service. 

Research to detect the novel coronavirus in wastewater is underway across the world, in an attempt to monitor the presence of the virus in communities, as a complement to directly testing individuals. Measuring the concentration of viral RNA in wastewater can show trends, such as whether infections are going up or down. Researchers are working to model the prevalence of infection, but there are many uncertainties, including contributing populations, excretion rates, stability of the indicators (including transformation in each unique wastewater system), sampling and sample preparation. Still, some like Biobot do provide prevalence estimates.

Wastewater testing can be part of the overall decision-making to manage the pandemic and would help determine whether more restrictions would be advisable in the future.

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