Los Angeles County has recorded 135 West Nile virus infections and five deaths this year, according to the county Department of Public Health's arbovirus report, with data through Sept. 24. The county said the number of people infected this season is greater than its five-year average for the same period.
The jump is steep. In all of 2025, the county documented 22 infections and two deaths. Earlier this month, the county described its count as the highest number of West Nile cases in nearly a decade. For a county of nearly 9.7 million people, the numbers remain small, but the share of serious illness among reported cases is high, and mosquito activity typically continues into October.
Nine in 10 Symptomatic Cases Reached the Nervous System
Of the 135 infections, 130 people had symptoms, and five were detected only when their donated blood or organs were screened. Blood banks test donations for West Nile virus, which helps keep infected blood out of the supply and sometimes identifies infections in people who never felt sick. Among those with symptoms, 120 had neuroinvasive disease, meaning the virus reached the brain or spinal cord.
That group included 91 cases of encephalitis, or brain inflammation, 20 cases of meningitis, and nine cases of acute flaccid paralysis, a sudden weakness of the limbs. Ten people had West Nile fever, a milder illness. The county has said nearly all severe cases required hospitalization.
Recovery from neuroinvasive disease can be slow. Some patients live with fatigue, weakness, or memory problems for months, and some never fully recover.
Reported numbers skew toward severe illness because milder infections often go untested. The CDC estimates that about 80% of infections cause no symptoms, and fewer than 1% lead to neuroinvasive disease.
Older Adults and Eastern Los Angeles County Carry the Heaviest Load
The median age of infected residents is 63, with cases ranging from age 4 to 101. Men account for 98 of the 135 infections. People over 60 and those with cancer, diabetes, high blood pressure, kidney disease, or organ transplants face the highest risk of severe illness and death.
The eastern Los Angeles County area accounted for 27% of infections, the South Bay for 25%, and the San Fernando Valley for 19%, according to the county report. Families caring for older parents in those areas may want to pay closer attention to evening mosquito exposure around the home.
Mosquito data point in the same direction. The Greater Los Angeles County Vector Control District has found 384 positive mosquito samples and 78 infected dead birds this year, compared with 104 samples and two birds at this point last year, MyNewsLA reported. "West Nile virus is cyclical, and the level of activity we see can look different each year," said Steve Vetrone, the district's assistant general manager of vector management services.
The district noted a telling detail. Virus activity is trending above the five-year average even though the number of native Culex mosquitoes remains below it, meaning a larger share of the mosquitoes present are carrying the virus.
A Busy Season Across California
Los Angeles County's surge fits a broader California pattern. The state has reported 210 human cases in 23 counties and 15 deaths in seven jurisdictions, according to the California West Nile Virus Website, updated Sept. 25. In August, the California Department of Public Health said overall West Nile activity had reached a five-year high.
MedicalDaily previously reported that earlier state-confirmed deaths were clustered in the Central Valley. Deaths have since been reported in Los Angeles and Orange counties, showing that serious illness is also reaching dense urban areas. County and state tallies are compiled on different schedules, so the numbers may not match on any given day.
There is no human vaccine and no specific antiviral treatment for West Nile virus. Care focuses on managing symptoms and, in severe cases, hospital support. That makes preventing bites the only practical protection for households.
Symptoms and Bite Prevention at Home
Mild symptoms can include fever, headache, body aches, rash, and fatigue, usually three to 14 days after a bite, according to the county. Severe illness may bring high fever, neck stiffness, confusion, muscle weakness, tremors, or paralysis. Anyone with those signs, especially an older adult, should seek urgent medical care.
Vector control officials recommend insect repellent containing at least 15% DEET, picaridin, IR3535, or oil of lemon eucalyptus. Intact window and door screens also help, as do loose long sleeves and pants at dawn and dusk, when Culex mosquitoes are most active. Older adults who garden, walk, or sit outdoors in the evening are among those who benefit most from these steps.
Residents can empty standing water from flowerpot saucers, buckets, birdbaths, and neglected pools each week. Dead birds and green pools can be reported to the local vector control district. The county updates its arbovirus report regularly through the end of the season.
Key Questions Answered
How many West Nile cases has Los Angeles County reported? 135 infections and five deaths as of Sept. 24, 2026.
How does that compare with last year? The county recorded 22 infections and two deaths in all of 2025.
What is neuroinvasive disease? An infection that reaches the brain or spinal cord, causing encephalitis, meningitis, or paralysis.
Who faces the highest risk? Adults over 60 and people with conditions such as cancer, diabetes, kidney disease, or organ transplants.
Is there a vaccine? No. Preventing mosquito bites is the main protection.
Which areas have the most cases? The eastern Los Angeles County area, the South Bay, and the San Fernando Valley.
Which symptoms need urgent care? High fever with a stiff neck, confusion, muscle weakness, tremors, or paralysis, especially in older adults.
Published by Medicaldaily.com
