Sewage tests reveal coronavirus in popular Yosemite National Park
Coronavirus has been detected in Yosemite National Park by testing raw sewage – a science that revealed dozens of people have had COVID-19 in Yosemite since the popular park reopened last month.
Mariposa County Health Officer Dr. Eric Sergienko told The Bee the test results show some in Wawona and Mariposa with coronavirus, and a “larger group” with the virus in Yosemite Valley – what he described as perhaps 100 people out of approximately 80,000 each week now visiting Yosemite.
Sergienko said that’s “not a bad number” and is far lower than many places with more coronavirus, including nearby Fresno County. Still, the weekly sewage samples suggest 10 times more people in the area with coronavirus than COVID-19 test results have shown, he said, attributed mostly to visitors.
Sergienko said Mariposa County’s first sewage sample to show COVID-19 was the week of June 30 through July 6.
That’s prior to a July 9 virtual meeting where Yosemite officials told community members that no Yosemite employees had tested positive for COVID-19.
When asked Friday if anyone in Yosemite has tested positive for coronavirus, spokespeople for the National Park Service and Yosemite’s concessionaire, Yosemite Hospitality, a subsidiary of Aramark, referred the question to the Mariposa County Department of Public Health, which then referred it back to Yosemite.
Sergienko said Mariposa County isn’t sharing where people have tested positive for coronavirus out of privacy concerns, since the county only has 18,000 residents. Yosemite National Park, however – which is federal jurisdiction but within Mariposa County – had more than 4.5 million visitors last year.
Mobile coronavirus testing is happening in Yosemite Valley and a health clinic in Yosemite Valley.
Evidence of coronavirus was detected in sewage by scientists looking for RNA – ribonucleic acid, a molecule similar to DNA. This testing has been done in other areas in the past to look for things such as the prevalence of opioids in a community, Sergienko said, and is now being used in some places to detect coronavirus.
Sergienko said he got the idea to do this testing locally from a colleague in Northern California. Mariposa County started its program in May and expanded it into the Yosemite area in June.
The sewage from Yosemite Valley was tested before it was treated at a wastewater treatment facility in El Portal, just outside the park’s west entrance along Highway 140. The county also continues to test sewage weekly in two other areas: the town of Mariposa, which is outside the park, and the Yosemite community of Wawona, near the park’s south gate along Highway 41.
Samples are sent to a lab in Massachusetts for testing. The San Francisco Chronicle reported that several private labs and universities have gotten into the business of looking for coronavirus this way over the past few months.
Sergienko sees it as “another piece of the puzzle” in COVID-19 surveillance. His office isn’t issuing any new restrictions in Mariposa County due to coronavirus at this time. He said COVID-19 is still considered contained in Mariposa County, with a low level of transmission. A Mariposa County health order remains in effect that requires hotel rooms be vacant for 24 hours before they are cleaned.
Yosemite is currently operating with some restrictions and a new day-use reservation system aimed to cut visitation in half, and Gov. Gavin Newsom announced some recent rollbacks due to growing cases of COVID-19 across the state.
This story was originally published July 17, 2020 at 4:42 PM with the headline "Sewage tests reveal coronavirus in popular Yosemite National Park."
