Orange County Reports First West Nile Deaths of 2026 after county health officials confirmed this week that older adults have died from infections linked to the mosquito-borne virus. The OC Health Care Agency announced the deaths on September 29 and said Orange County has now reported 36 West Nile virus infections this year. Officials are urging residents and visitors to continue taking mosquito precautions as Southern California remains warm enough for mosquito activity to continue well into the fall.
Orange County Has Reported 36 West Nile Infections
The OC Health Care Agency said the first human deaths associated with West Nile virus infection in Orange County this year were confirmed in older adults during the final week of September. The county has reported 36 human infections in 2026, but health officials caution that the actual number of infections is likely higher because many people infected with West Nile virus never develop symptoms and are never tested. Most people who become infected do not become seriously ill. When symptoms do occur, they can include fever, headache, body aches and fatigue. A smaller number of patients develop neuroinvasive disease, which can affect the brain or nervous system and may cause severe headache, neck stiffness, confusion, muscle weakness, paralysis or vision problems. Older adults and people with certain underlying medical conditions face a higher risk of severe illness.
Mosquito Treatments Are Continuing This Week
The deaths were announced as the Orange County Mosquito and Vector Control District continues large-area mosquito control operations around the county. Truck-mounted ultra-low-volume treatments are scheduled from September 30 through October 2 in Fullerton and La Habra using DeltaGard, while Garden Grove and Westminster are scheduled for treatments using AquaDuet. The district lists mosquito abundance as the reason for the current applications. Orange County has conducted numerous truck-mounted treatments throughout the summer in cities including Anaheim, Buena Park, Cypress, Fullerton, Garden Grove, Huntington Beach, La Habra, Los Alamitos, Mission Viejo, Stanton and Westminster. The continuing treatments underscore that mosquito season has not ended simply because the calendar has moved into fall.
West Nile Virus Is Spread by Mosquitoes
West Nile virus is primarily transmitted through the bite of an infected mosquito. Mosquitoes become infected after feeding on infected birds and can then transmit the virus to people and other animals during later blood meals. The virus is not generally spread through casual person-to-person contact. Because mosquitoes need standing water to develop, residents can reduce local breeding opportunities by regularly checking buckets, plant saucers, children’s toys, clogged gutters, birdbaths and other objects that can collect water around homes. Even small amounts of water can support mosquito larvae when temperatures remain favorable. Health officials also recommend using an EPA-registered insect repellent and wearing clothing that reduces exposed skin when mosquitoes are active.
Late September Does Not Mean Mosquito Season Is Over
Southern California’s mild climate allows mosquito activity to continue much later than residents in colder parts of the country may expect. Warm daytime temperatures can allow adult mosquitoes to remain active, while containers around homes can continue producing new mosquitoes if water is left standing. That means residents who stopped checking their yards after summer may still have active breeding sites in late September and October. Screens on windows and doors should also be inspected for damage, especially in homes where mosquitoes are being noticed indoors. PestMarket’s Mosquito Control Guide covers additional steps homeowners can take to identify breeding sites and reduce mosquito activity around their property.
Why Older Adults Face Greater Risk
The first confirmed deaths in Orange County this year involved older adults, a group public-health agencies consistently identify as being at greater risk for severe West Nile disease. While anyone can be infected, the chance of developing serious neurological complications increases with age and certain health conditions. Families with older relatives should not assume mosquito precautions are only necessary during outdoor recreation. Bites can occur around patios, gardens, driveways and other familiar areas close to home, especially when mosquito populations are elevated nearby. Reducing standing water and using repellent remain important even during short periods spent outdoors.
Why This Season Matters
West Nile virus activity can vary significantly from year to year, which is why local surveillance remains important. Mosquito control districts monitor mosquito populations, test samples for viruses and use those results to decide where additional control measures may be needed. Human case reports provide another indication of transmission but represent only part of the overall picture because many infections cause no symptoms. The confirmation of Orange County’s first deaths of 2026 is therefore more than a statistical milestone. It is a reminder that mosquito-borne disease remains an active public-health concern even as summer ends.
For Orange County residents, the most useful response remains straightforward: remove standing water, keep screens in good condition, use insect repellent when appropriate and continue paying attention to local mosquito-control notices. With treatments still underway this week, officials are clearly signaling that mosquito activity remains high enough in parts of the county to warrant continued action.