Los Angeles County's first human West Nile virus case of 2026 hospitalized an Antelope Valley resident with brain inflammation, health officials announced Monday, July 13. The patient developed symptoms in late June and was diagnosed with West Nile virus encephalitis, a severe form of the disease that affects less than 1% of those infected but can cause fever, altered mental status, and movement disorders, according to the CDC.
"Mosquitos thrive in hot weather, increasing the risk of bites and mosquito-borne diseases," said Dr. Muntu Davis, Los Angeles County Health Officer, urging residents to take precautions as temperatures climb.
Mosquito activity far above average
The Greater Los Angeles County Vector Control District had detected 38 West Nile virus-positive mosquito samples as of early July, compared to a five-year average of roughly four at this point in the season, according to Caroline Gongora, the district's public information coordinator. Infected mosquitoes have been found in Sunland, Woodland Hills, Tarzana, and Northridge, all in the San Fernando Valley, with Sunland about 10 miles from Pasadena. No positive mosquito pool in Pasadena itself has been publicly reported.
Statewide, three human cases have been confirmed so far in 2026: the new LA County case, one in Sacramento County, and one in Long Beach. Nationally, the CDC reported at least 48 human cases as of June 30, including 38 cases of severe neuroinvasive disease, the highest midyear total since 2004, according to the LA Times.
LA County averages 41 human West Nile cases per year over the past five years, though the department notes the true number of infections is far higher because most people experience no symptoms or only mild illness. About 1 in 10 people who develop severe neuroinvasive West Nile disease die, according to the CDC.
Heat warning compounds the risk
The National Weather Service has issued an Extreme Heat Warning for Pasadena in effect from Tuesday, July 14, at 10 a.m. through Thursday, July 16, at 8 p.m., with highs forecast between 90 and 105 degrees across the LA County interior by Wednesday. Overnight lows are expected to stay in the 70s, offering little relief.
Monsoonal moisture moving into the region will raise humidity, making the heat feel worse, according to NWS Oxnard meteorologist Ariel Cohen.
The warning flags a high risk of dangerous heat illness for young children, older adults, people without air conditioning, and anyone active outdoors. People over 50 and those with preexisting health conditions also face higher risk of serious illness from West Nile virus.
How to protect yourself
LA County health officials recommend:
- Use EPA-registered insect repellent containing DEET, IR3535, oil of lemon eucalyptus, or Picaridin.
- Dump standing water from buckets, plant saucers, and clogged gutters. Even small amounts of water can breed mosquitoes.
- Keep swimming pools clean and chlorinated.
- Install or repair window and door screens.
- Avoid outdoor activity between dusk and dawn, when West Nile-carrying mosquitoes are most active. Wear long sleeves and pants if you must be outside.
West Nile virus has no vaccine and no specific treatment. It has been present in California since 2003 and has killed more than 400 people statewide.
Residents can report neglected pools, large mosquito breeding sites, or dead birds to the Greater Los Angeles County Vector Control District online at glamosquito.org.
