City of Long Beach 
Public Information Office
411 W. Ocean Blvd, 
Long Beach, CA 90802

FOR IMMEDIATE RELEASEPress Release # 110923-5
Long Beach Health Department Confirms Human Case of St. Louis Encephalitis
Mosquito-borne disease rarely seen in Los Angeles County
Amanda Recio
Public Affairs Specialist
Department of Health and Human Services

Long Beach, CA – The City of Long Beach Department of Health and Human Services (Health Department) has confirmed a case of St. Louis Encephalitis (SLEV). This is the first documented human case of SLEV in Long Beach since 1984. The risk of local exposure remains low, and the Health Department is taking steps to prevent further spread of the virus that causes SLEV. The person who was infected was hospitalized but is now recovering at home. No other suspected cases have been identified. As of Nov. 3, 2023, 12 human cases of SLEV have been reported in California this year. The Health Department is educating healthcare providers and working with local vector control agencies to monitor the situation.

"We are working diligently with healthcare providers to educate the community to prevent more cases of SLEV,” said Mayor Rex Richardson. “Mosquito control is a shared responsibility and residents must take an active role in reducing the threat of mosquito-borne illnesses in their neighborhoods.”

SLEV is a disease that is caused by the St. Louis Encephalitis virus and is spread to people by the bites of infected culex mosquitoes. It is in the same virus family as West Nile Virus (WNV), with similar symptoms and transmission, but is less common in California. It is not spread from person to person. Most people who are infected will not experience symptoms, but those who do typically have mild symptoms that may include fever, headache and nausea.

Although everyone is at risk for SLEV, people over 50 years of age and those with underlying health conditions are at greater risk of more serious symptoms. Severe SLEV affects the brain and nervous system and can cause stiff neck, confusion, dizziness and sometimes death. There are currently no vaccines or medicines to prevent or treat SLEV, but health care providers can recommend treatments to aid recovery, including fluids, rest and medication for pain or fever.

Mosquitoes that transmit SLEV are most active at dusk and dawn. Residents that are outside during the cooler hours of the morning and night are encouraged to take the following measures to protect themselves:

  • Use a mosquito repellent with DEET, IR3535, picaridin or products containing oil of lemon eucalyptus (do not use oil of lemon eucalyptus on children younger than 3 years old).
  • Wear loosely fitted, long-sleeved shirts and long pants.
  • Eliminate standing water around clogged rain gutters, rain barrels, discarded tires, buckets, watering troughs and anything that holds water for over a week.
  • Keep weeds, vines, hedges and grass trimmed; adult mosquitos like to rest in vegetation.
  • Change water in pet dishes, birdbaths and other small containers weekly.
  • Ensure that swimming pools, spas and ponds are properly maintained.
  • Report neglected swimming pools and other mosquito control issues in your neighborhood to the Health Department’s Vector Control Program.

“The first confirmation of SLEV in Long Beach should serve as a reminder that we need to protect ourselves against mosquitoes,” said Health Officer, Dr. Anissa Davis. “The Health Department encourages everyone to continue reporting issues regarding mosquito control in their area.”

The Health Department monitors and investigates mosquito-borne illnesses and has enhanced these efforts in response to this case. The Department’s Vector Control team regularly sets traps and tests samples of the mosquitoes found in Long Beach. To date, no mosquito samples have tested positive for SLEV.

For more information, people are encouraged to visit

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