Stanislaus County has confirmed its first human case of West Nile virus for 2026, health officials announced, as state surveillance data shows mosquito-borne virus activity running at a five-year high across California. The news comes just days after crews sprayed pesticide over Empire and rural west Modesto to knock down adult mosquito populations before the disease could spread further.
A Season Already Flagged As Severe
The Stanislaus County Health Services Agency did not specify where in the county the infected resident was exposed, according to a press release cited by CBS Sacramento. The agency noted that the last significant increase in human West Nile cases in the county occurred in 2023. Dr. Thea Papasozomenos urged residents to protect themselves and their families from mosquito bites, saying current surveillance indicators point to a severe West Nile season in 2026 with concern for a higher number of human cases, per the same report.
The timing lines up with aggressive vector control action on the ground. The East Side Mosquito Abatement District conducted low-volume aerial spraying of Dibrom over Empire and rural west Modesto this past Thursday to suppress adult mosquitoes carrying the virus, according to a community notice posted on Facebook. The district’s spraying authority operates under the California Health and Safety Code across a roughly 540-square-mile area north of the Tuolumne River.
Mosquito Pools Climbing Week Over Week
Environmental surveillance backs up the concern. The California Department of Public Health logged 28 newly positive mosquito pools in Stanislaus County for the week ending August 21, up from 25 positive pools the week before, according to state data. Those numbers reflect viral amplification already underway in local mosquito populations before this human case was confirmed.
Statewide, the picture looks similarly alarming. Twenty-four percent of tested dead birds in California have come back positive for West Nile virus through mid-August, compared with a five-year average of 13%, while mosquito positivity has reached 8 per 1,000 tested versus a five-year average of 5 per 1,000, as reported by Hey SoCal. Dead birds are considered a warning sign of West Nile activity in an area, and Californians can report them to the state’s dead bird hotline at westnile.ca.gov or by calling 877-968-2473.
Statewide Case Count Nearly Triples Last Year’s Pace
California has recorded 46 human West Nile virus cases in 2026 as of August 21, compared with just 14 cases at the same point in 2025, per state figures cited by CBS Sacramento. Of those 46 cases, 87% — 40 patients — involved severe neuroinvasive disease, with a median patient age of 63 and 54% identified as male, according to the California Department of Public Health. The state has also recorded four West Nile fatalities in 2026, occurring in Butte, Fresno, Glenn, and Kings counties…