The mosquito-borne West Nile virus has infected at least four Philadelphia residents since late July and claimed one life.

All of the residents who developed the virus were age 65 or older, and all of them required hospitalization because their cases were neuroinvasive, according to surveillance data released by the Philadelphia Department of Public Health.

The resident who died, a man in his 80s, became ill Sept. 1, according to the health department.

His death was reported this past Tuesday, information from the state West Nile Virus Control Program indicates.

Public health and environmental workers test and monitor Philadelphia mosquito pools for West Nile Virus each year from May through October.

At 13 percent through Oct. 4, the city's mosquito pool positivity rate has jumped from last year's rate of 3 percent, according to health department data.

The positivity rate remains lower than the 18 percent reported in 2012, considered a peak season for West Nile Virus activity.

That year, nine human West Nile Virus cases, two of them fatal, were reported in Philadelphia, according to the health department.

Though there is no known vaccine or cure for West Nile Virus, between 70 and 80 percent of those who become infected do not develop any symptoms, according to the U.S. Centers for Disease Control and Prevention.

Those who do can experience symptoms ranging from a fever and headache to serious neurological illness, including inflammation of the brain and surrounding tissues, according to the CDC.

Nationwide, a total of 1,444 human West Nile Virus cases and 49 West Nile deaths have been reported this year, as of Oct. 14, according to CDC data.

Including the four in Philadelphia, Pennsylvania has seen a total of eight human West Nile Virus cases this year, state and CDC data indicate. Two of the cases occurred in Bucks County, and one each was reported in Allegheny and Dauphin counties.

Other than the Philadelphia man, no additional West Nile Virus-related deaths have been reported this year in Pennsylvania.

Until temperatures drop and the first hard frost of the season occurs, residents are advised to take steps to protect themselves from mosquito bites, including using insect repellent and wearing long pants and sleeves when outdoors, particularly during dawn and dusk.

Contact Alex Wigglesworth at 215-854-2305 or awigglesworth@philly.com. Follow @phila_lex on Twitter.
Contact the Breaking News Desk at 215-854-2443; BreakingNewsDesk@philly.com. Follow @phillynews on Twitter.