Pasadena recorded its first West Nile virus-positive mosquito sample of the year on Aug. 13. Across the San Gabriel Valley, the total has surged to 105, topping the five-year average, the San Gabriel Valley Mosquito and Vector Control District announced Thursday, Sept. 3.

The district's count stood at 63 as of Aug. 17. It hit 105 by the time the detection table was last updated Aug. 31, spanning 26 cities and unincorporated communities.

Nearby Altadena has logged three positive samples since July 23, and South Pasadena has recorded four since Aug. 4. No human West Nile virus case had been confirmed in Pasadena as of Aug. 21.

West Covina leads the district with 12 positive samples, followed by Covina with 11, Rosemead with nine, Monterey Park and Temple City with seven each, and Alhambra with six. Alhambra's first detection on June 23 was the earliest on the district's list.

Tristan Hallum, director of scientific programs for the district, said technicians are treating known mosquito breeding sites and searching for new ones in communities with elevated activity.

"We strongly encourage residents to tip out any stagnant water around their homes, toss out any unused containers that can collect water, and protect themselves with mosquito repellent when outdoors during this holiday weekend," Hallum said.

Susanne Kluh, general manager of the Greater Los Angeles County Vector Control District, attributed the early and widespread activity to the warmest winter on record. Detection in Los Angeles County started almost two months ahead of the usual timeline, Kluh said in an Aug. 20 county advisory, as reported by Altadena Now.

Statewide, eight of every 1,000 mosquitoes were testing positive as of Aug. 20, compared with a five-year average of five per 1,000, according to the California Department of Public Health. The state had reported 65 human cases across 16 counties and more than 3,000 positive mosquito samples as of Aug. 28.

Los Angeles County confirmed its first West Nile virus death of the season on Aug. 20. The victim was a San Fernando Valley resident who developed severe neurological illness. Fifteen human infections had been documented in the county as of the same date, excluding Long Beach and Pasadena, which report separately through their own health departments.

The Pasadena Public Health Department recommends what it calls the "Three Ds." Use an EPA-registered repellent containing DEET, picaridin, oil of lemon eucalyptus or IR3535. Wear long sleeves and pants at dawn and dusk, and keep tight-fitting screens on windows and doors. Drain standing water from flowerpots, buckets, tires and other containers.

About 80% of people infected show no symptoms. Roughly 20% develop a mild fever. Less than 1%, about one in 150, develop severe neurological illness such as meningitis or encephalitis, according to the Pasadena Public Health Department. Older adults and people with weakened immune systems face the greatest risk.

There is no vaccine or cure.

Residents can report neglected swimming pools or mosquito problems to the district at (626) 814-9466 or at SGVmosquito.org.