West Nile virus has killed 10 people in Los Angeles County in 2026, with infections topping 200 as a hot, humid summer fueled the worst mosquito season in nearly a decade.
The county recorded 22 West Nile infections and two deaths in all of 2025, KTLA reported. The county's five-year average is 41 cases per season.
The LA County Department of Public Health attributed the surge to the warmest winter on record, which pushed virus activity to begin almost two months earlier than usual. El Niño weather patterns brought tropical moisture and high humidity to Southern California, accelerating mosquito larva development and speeding population growth.
The season's first case surfaced in late June, when an Antelope Valley resident was hospitalized with West Nile encephalitis, the county reported. By Aug. 20, the county confirmed its first death of the year, a San Fernando Valley resident who died from neurological illness. At that point, half of the county's infections were concentrated in the San Fernando Valley.
Cases doubled fast. By Sept. 21, the county had hit 100 infections and five deaths, the highest early-season count in nearly a decade. The last comparable year was 2017, when 268 cases were reported for the entire season. The 2026 season has already surpassed that mark with weeks of mosquito activity remaining.
"West Nile virus can cause serious illness, and the number of severe cases and deaths we are seeing this year is concerning," LA County Health Officer Dr. Muntu Davis said in the county's Sept. 21 announcement.
Joseph Vazquez, a 13-year-old from Long Beach, was hospitalized at Children's Hospital Los Angeles after developing a severe case complicated by transverse myelitis, a rare spinal cord inflammation, USA Today reported on Oct. 6. Vazquez lost the use of his legs, bladder and bowel control.
The Greater Los Angeles County Vector Control District said it detected 384 West Nile-positive mosquito samples and 78 infected dead birds in 2026 as of late September, compared with 104 positive samples and two positive birds at the same point in 2025, according to Spectrum News. Steve Vetrone, the district's assistant general manager, said teams stepped up inspections, control treatments and public outreach after detecting elevated activity early in the season.
Statewide, California had recorded 252 human cases and 19 deaths as of Oct. 8, about five times higher than the same point last year, according to epidemiologist Dr. Matt Willis, a former Marin County public health officer who tracks the data in a Substack newsletter. LA and Orange counties together accounted for the highest regional burden.
Orkin's 2026 rankings named Los Angeles the most mosquito-infested city in the country for the sixth straight year.
There is no vaccine or specific treatment for West Nile virus. About 1 in 5 infected people develop symptoms such as fever, headache and body aches. About 1 in 150 require hospitalization. People over 50 and those with existing health conditions face the greatest risk of severe illness, including meningitis, encephalitis and limb paralysis, according to the county health department.
Peak mosquito season runs from June through November. The county case count excludes Long Beach and Pasadena, which operate their own health departments.
Residents can report dead birds to the California Department of Public Health at 1-877-WNV-BIRD and call 2-1-1 to report persistent mosquito problems. The LA County Public Health InfoLine is available at 1-833-540-0473, open daily from 8 a.m. to 8 p.m.
