Orange County health officials said Tuesday an elderly Seal Beach woman died from complications associated with West Nile virus — the first confirmed fatality this year in Southern California and the fifth in the state.

The unidentified woman, who was in her 80s, had underlying medical conditions when she contracted the virus, which developed into West Nile Neuroinvasive Disease.

With 40 reported infections, Orange County leads the state in the number of West Nile virus infections this year, and is a substantial increase from the previous four years when there were fewer than five infections at this time of year.

On Tuesday, Long Beach Health Officer Dr. Mitchell Kushner confirmed seven total cases have been reported in the city, the first of which was reported on Aug. 7. The virus is appearing earlier and more aggressively this year than in years past, and he said there are several possible factors that could be contributing to the increase.

“The climate has to be perfect for the mosquito and it has been warm earlier this year,” he said. “We are in the height of West Nile season.”

West Nile virus peak months are August and September but cases can continue throughout the fall.

“We have this every year so every year, this is going to be a concern,” he said.

One Long Beach case this year involves a 72-year-old Belmont Shore resident who is still in the Intensive Care Unit after being diagnosed with West Nile virus Aug. 19. His symptoms began one week earlier, on Aug. 13, and rapidly progressed from body aches and nausea to difficulty breathing and loss of speech within a matter of days.

Doctors at Los Alamitos Medical Center said he has contracted meningoencephalitis, a neuroinvasive disease that causes swelling in the brain, according to the Centers for Disease Control and Prevention.

“He is our most severe case,” Kushner said. “Hopefully we hear he is doing better soon.”

Ten days after being admitted to the ICU, the patient’s condition is relatively the same, family members said Tuesday. His stepdaughter, Taylor Kalander, said he is more alert and aware of people in the room with him, and is able to respond to questions by nodding his head. She said the family is optimistic about his recovery.

According to the Centers for Disease Control and Prevention, less than 1 percent of people who are infected with the virus develop West Nile Neuroinvasive Disease. Approximately 80 percent of people who contract the virus have no symptoms, leading health officials to believe the number of people infected is actually much higher than the numbers show.

West Nile virus is passed by mosquitoes; it is not contagious among people.

Symptoms usually develop within three to 14 days of being bitten, although only one in 150 persons infected with the virus develop symptoms, which include fever, headache, body aches and occasional rash. Even fewer people develop more symptoms, including stiff neck, tremors, muscle, weakness, numbness and paralysis.

City health officials urge residents and business owners to remove pools of standing or stagnant water, such as flowerpots, bird baths, pet water dishes and gutters, which are breeding grounds for mosquitos, and to maintain swimming pools and spas with proper filtration and chlorination levels because green or dirty pools can breed thousands of mosquitos in a week’s time.

People should wear long sleeves and pants when they are outside between dusk and dawn as well as use mosquito repellents containing DEET, picaridin and some oil of lemon eucalyptus. Lastly, officials suggest making sure that doors and windows have tight-fitting screens and are in good repair.

There is currently no vaccine or antiviral treatments for the West Nile virus.