Yosemite national park officials suspect hundreds of visitors this summer may have had COVID-19 after testing sewage.
The county health department has been collecting untreated wastewater flowing from Yosemite Valley for testing, according to the San Francisco Chronicle. Prior to the testing, no one had tested positive for the virus through nasal swab testing at the park’s health clinic.
Biobot Analytics in Cambridge, Massachusetts, examined the sewage water to determine if there are traces of genetic material from Sars-CoV-2 in the human feces. From the traces in samples, the number of people passing through Yosemite who might be infected with the coronavirus at that time can be determined.
The county began testing the wastewater from the Yosemite Valley in June. Based on the data accumulated so far, health officials believe an estimated 170 people in the park the week of the Fourth of July may have been infected with the coronavirus, reported the Guardian. That number dropped to 60 the following week.
A neighboring community also had its wastewater tested, and the estimate went down from 60 to 50 over that same two-week period.
“For me that suggests that indeed the volume that we saw on the Fourth was directly related to visitors to the area,” said the Mariposa county health official Dr Eric Sergienko.
Mariposa county will continue testing the sewage water every week and maintaining safety protocols currently in place.
The park closed its gates in March, but now that it has reopened it requires visitors to make reservations to get in, cutting attendance by about half of what it was in June 2019.