California health officials are urging residents to take precautions against mosquito bites after Stanislaus County confirmed its first West Nile virus‑associated death of 2026, a season already marked by the highest statewide activity in five years.
The Stanislaus County Health Services Agency said the individual, an adult under 50, died from a neuroinvasive form of the virus. As of Sept. 22, the county had reported 11 human cases this year. Public Health Officer Dr. Thea Papasozomenos said the death underscores that severe illness can strike people of any age.
Statewide, West Nile virus activity continues to climb. The California Department of Public Health reports signs of the virus in 37 counties through mosquito testing, dead birds, sentinel chickens and horses. Twenty‑three counties have confirmed human cases. As of Sept. 25, California had recorded 210 human infections and 15 deaths.
Indicators of virus circulation are also above average. More than 24% of dead birds tested through surveillance have been positive for West Nile virus, compared to a five‑year average of 13%. Mosquito samples are showing higher infection rates as well — eight out of every 1,000 mosquitoes tested are carrying the virus, up from the five‑year average of five.
“West Nile virus can be fatal, particularly for the elderly and immunocompromised,” said Dr. Erica Pan, CDPH director and state health officer. “August and September are peak periods of transmission in the state, so we urge everyone to take precautions.”
Risk factors for severe illness include being 60 or older, having diabetes, hypertension or chronic kidney disease, or taking medications that suppress the immune system. The CDC recently issued a health alert noting that patients on certain immunosuppressive drugs face significantly higher risks of long‑term complications or death.
According to the Westnile.ca.gov website, which tracks county data, Stanislaus County has reported six human cases, one dead bird, 155 positive mosquito samples and one infected horse as of Sept. 25. Merced County has confirmed two human cases, two dead birds, 82 positive mosquito samples and one horse. Merced’s positive mosquitoes have been found in communities including Gustine, Los Banos, Hilmar, Delhi, Livingston, Atwater and Merced. The state website data can be behind the local county data, which is why the human cases are different for Stanislaus County.
Stanislaus County confirmed its first human case of the season on Aug. 24. Days later, the Turlock Mosquito Abatement District reported three additional neuroinvasive cases, including one in Newman, all requiring hospitalization. Merced County announced its first case on Sept. 2 in Planada.
Health officials continue to emphasize prevention. CDPH recommends the “Three Ds”:
- DEET — Use EPA‑registered repellents containing DEET, picaridin, oil of lemon eucalyptus or IR3535.
- Dawn and dusk — Wear long sleeves and pants and use repellent when mosquitoes are most active. Ensure window and door screens are intact.
- Drain — Remove standing water from containers, tires, buckets and other items where mosquitoes lay eggs. Report neglected swimming pools to local mosquito control agencies.
Dead birds, a key indicator of West Nile virus activity, can be reported to the California West Nile Virus Hotline at 1‑877‑WNV‑BIRD or online at westnile.ca.gov/report.
Westside residents can report mosquito issues to the Turlock Mosquito Abatement District at (209) 634‑1234 in Stanislaus County or the Merced County Mosquito Abatement District at (209) 722‑1527.
“This is not the time to let your guard down,” Merced County officials said. “Mosquitoes active at dusk and dawn can transmit West Nile virus.”
