COVID-19 levels run high in Bay Area wastewater, prompting calls for precautions

Grant Stringer, Bay Area News Group on Jul 25, 2026

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Public health officials and infectious disease experts are urging Bay Area residents to take added precautions against COVID-19 as wastewater testing shows high concentrations of the virus in parts of the region.

Measurements at wastewater treatment plants in Santa Clara County and San Francisco have shown high concentrations of the virus over the past three weeks, while concentrations have reached medium levels on the Peninsula and in the North Bay. Wastewater testing serves as a proxy for the virus’s spread because it does not depend on people seeking tests or reporting their results.

Virus levels remain far below those recorded during California’s surge last summer. Still, officials and experts said the latest increase warrants precautions.

“High levels of COVID in the wastewater mean that each person is encouraged to take extra precautions to keep from getting sick and to help slow the spread of COVID, especially when so many people are traveling for summer,” a Santa Clara County Public Health Department spokesperson said in a statement.

Officials recommended wearing masks in crowded indoor settings, staying current on vaccinations, testing for the virus and remaining home when sick.

Peter Chin-Hong, an infectious disease expert at UC San Francisco, said he expects COVID-19 to spread more widely through the Bay Area this summer, continuing a pattern of summertime surges in 2024 and 2025. Most people are not at risk of becoming severely ill, he said.

“For most people, it’s annoying and can cause serious symptoms and string you up in bed for some time,” Chin-Hong said. “But it’s not going to be life-threatening.”

Older adults, pregnant women and young children face greater risks and should take particular care to avoid infection, Chin-Hong said. Adults 75 and older should make sure they have received a COVID-19 vaccination within the past six months, which reduces the risk of serious illness and may help prevent infection for up to three months, he said.

Parents preparing their children to return to school should also consider vaccination, Chin-Hong said. The California Department of Public Health recommends COVID-19 vaccination for children as young as 6 months.

Santa Clara County has recorded progressively fewer COVID-19 hospitalizations and deaths since the early years of the pandemic, before vaccines became available and broader immunity developed. Unvaccinated people in their mid-70s or older now account for most deaths caused by the virus, Chin-Hong said.

Interest in COVID-19 vaccination plummeted after the federal public health emergency ended in 2023. About 18% of Santa Clara County residents are up to date on their vaccinations, compared with roughly 11% of Californians, according to the state health department.

Public health officials are also urging parents to vaccinate their children against measles as the highly contagious virus spreads across the country.

California requires most school-age children to receive two doses of the measles, mumps and rubella vaccine, allowing exemptions only for specific medical conditions. Parents who object to vaccination may homeschool their children under a 2015 law signed by then-Gov. Jerry Brown.

California has confirmed 52 measles cases this year, putting the state on track for its highest annual total since 2015, according to the state Department of Public Health.

Nationally, measles cases are on track to reach their highest level since 2000. During the first seven months of 2026, the country recorded 2,318 cases, surpassing the total for all of 2025, according to the Centers for Disease Control and Prevention.

Vaccination rates among kindergartners are declining in parts of the country but remain high in the Bay Area. Even so, public health officials have expressed concern about declining confidence in the well-established science supporting measles immunization.

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