Year's First 2 Human Cases Of West Nile Virus Confirmed In Bay Area

SANTA CLARA COUNTY, CA — Two Santa Clara County residents have tested positive for West Nile virus, marking the Bay Area's first confirmed cases of 2026, health officials announced Wednesday.

The announcement comes as the Santa Clara County Mosquito and Vector Control District also detected West Nile virus-positive mosquitoes for the first time this year.

The district said it will conduct targeted treatments to reduce the adult mosquito population, with treatment locations and times to be announced.

The two infected residents are adults, officials said. One was hospitalized and the other was treated in an emergency department before both were released to recover at home, according to the Santa Clara County Public Health Department.

Health officials said the cases are unrelated, and because both individuals traveled during the virus's incubation period, it is unclear whether they contracted the virus in Santa Clara County or elsewhere.

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"Taking swift action is critical to protect public health when a West Nile virus mosquito is detected," said Jeremy Shannon, assistant manager of the Santa Clara County Mosquito and Vector Control District, in a statement. "Adult-mosquito-control treatments reduce the flying adult mosquito population in the area, which decreases the risk of a West Nile virus-human infection."

West Nile virus is the most common mosquito-borne disease in California, according to the California Department of Public Health. About 80 percent of people infected never develop symptoms, while roughly 20 percent experience flu-like symptoms such as fever, headache and body aches. Fewer than 1 percent develop severe neurological illness, with older adults and people with certain medical conditions at the greatest risk, the CDPH reported.

"Unfortunately, there is no vaccine that prevents West Nile virus, so please take extra care to prevent these mosquitoes from spreading and infecting people by dumping standing water around your home and property," said Dr. Krishna Surasi, assistant health officer and communicable disease controller for the County of Santa Clara Public Health Department. "Use EPA-registered insect repellents, and wear pants and long sleeves, especially if you are outside at dawn and dusk when the mosquitoes that spread West Nile virus are most likely to bite you."

Residents can help reduce mosquito breeding by emptying standing water from containers such as flowerpots, buckets and pet bowls, and by reporting neglected swimming pools or dead birds that may be signs of West Nile virus activity.

The Mosquito and Vector Control District stated it will provide additional information about upcoming mosquito-control treatments as plans are finalized.

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