No one had tested positive via nasal swabs, but researchers’ investigation tells a different story

Yosemite national park officials suspect that hundreds of visitors this summer may have had Covid-19 thanks to an unorthodox approach – testing sewage.

The San Francisco Chronicle reported last week that the county health department has been collecting untreated wastewater flowing from the idyllic Yosemite Valley for testing. Prior to this effort, according to the Chronicle, no one had tested positive for the virus through nasal swab testing at the park’s health clinic. Scientists at a lab called Biobot Analytics in Cambridge, Massachusetts, have examined the sewage water to determine if there are traces of genetic material from Sars-CoV-2, the coronavirus that causes Covid-19, in the human feces. From the traces in a given sample, they can estimate how many people passing through Yosemite might be infected with Covid-19 at that time.