West Nile virus cases hit decade high in Los Angeles County, with South Bay accounting for a quarter of infections
Human cases of West Nile virus in Los Angeles County have risen to a ten-year peak, and the South Bay region now accounts for about 25% of those cases, most of which are neuroinvasive.
Human infections of West Nile virus across Los Angeles County have reached the highest level in a decade, according to data from the Greater Los Angeles Vector Control District. The South Bay, traditionally less affected, now represents roughly one-quarter of all county cases, and nearly all of those have progressed to neuroinvasive disease.
The virus, which circulates among wild birds and is spread by mosquito bites, has been endemic in California since its first detection in 2003. Over the past 23 years more than 8,000 Californians have been infected and more than 400 have died. While about 80% of infections are asymptomatic, the remaining cases can range from flu-like illness to severe meningitis or encephalitis, which may cause lasting neurological damage or death.
"It’s just really unusual for these coastal cities to have early activity and activity this high," said Susanne Kluh, general manager of the Greater Los Angeles Vector Control District, attributing the surge to an unusually warm winter that kept temperatures higher for longer.
Health officials emphasize that there is no vaccine or specific treatment for West Nile virus; care is limited to hospitalization, fluids and pain management. The county’s vector-control program targets female Culex mosquitoes from May through November to reduce transmission risk.
Hospitals in the South Bay, including Torrance Memorial Medical Center, Kaiser Permanente South Bay Medical Center and Harbor-UCLA Medical Center, have reported markedly higher case numbers than in previous years. Kaiser Permanente noted 25 confirmed infections this season after recording none in the two prior years. The Los Angeles County Department of Public Health reports 216 infections statewide so far, up from 22 the previous year, with 189 cases classified as neuroinvasive.
The median age of patients is 64, and the majority are male. While older adults and immunocompromised individuals are at higher risk, younger patients have also experienced severe outcomes, such as a 13-year-old from Long Beach who developed transverse myelitis and lost mobility.
"West Nile virus can cause serious illness, and the number of severe cases and deaths we are seeing this year is concerning," said Los Angeles County Health Officer Muntu Davis in a written statement, urging residents to use insect repellent, eliminate standing water and ensure screens are intact.
Medical experts note that the rarity of symptomatic cases hampers funding for vaccine development and clinical trials. Although several vaccine candidates have been tested, none have reached the market, and most therapeutic studies have been inconclusive.
Public health officials continue to stress preventive measures, especially for older adults and those with weakened immune systems, and advise seeking medical care promptly if fever, headache, rash or neurological symptoms develop after a mosquito bite.