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West Nile Virus

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On May 8th, the first mosquito pool infected with West Nile Virus (WNV) in Philadelphia for the 2024 season was collected in Northeast Philadelphia. Since May, positive pools have been identified at 12 sites across the City. The WNV pool positivity in 2024 has started to increase earlier compared with the year-to-date historic median rate from 2001–2023 (5% vs 0%). No human cases have been reported in the City this season, but increased risk for human infection will continue in Philadelphia until the first hard frost occurs.

From May through October, PDPH, in collaboration with the PA Department of Environmental Protection, conducts mosquito management activities throughout Philadelphia, which entails surveillance and identification of mosquito pools, testing pools for WNV, and control activities (eliminating breeding sites, larviciding catch basins, ground spraying, etc.). Since May 2024, 40 locations in Philadelphia were treated to control larval mosquito populations and two locations to control adult mosquito populations.

Click here for more information on West Nile Virus and other arboviruses, including disease guidance and reporting information.

Click here to download the latest 2024 West Nile Virus report in a printable format.

Click here to download the 2022 season summary report of West Nile Virus in a printable format.

West Nile Virus Mosquito and Human Case Surveillance, Philadelphia PA, Morbidity Week 26 and Cumulative 2024 Season Update

Week 26 (6/23) - 6/29)

2024 Season (5/1 - 6/29)

Mosquito Pools Tested



WNV Positive Pools



Human WNV Cases



Neuroinvasive WNV



WNV Fever



Human WNV Deaths



Presumptive Viremic Donors



*298 mosquito pools at 66 different mosquito trapping sites

mapwithlegend_2024 (3)

Advise your patients to:

  • Use repellent with DEET ( ≥ 20% to also prevent tick bites), Picaridin, or oil of lemon eucalyptus when outdoors.
  • Regularly check and remove standing water outside their home (e.g. unused pools, tires).
  • Keep well-fitted screens on windows and doors.
  • Report mosquito problems and dead bird sightings to the PDPH Vector Control Program's Mosquito Complaint Line at 215-685-9000.

WNV Testing and Reporting Requirements for Human Surveillance in Philadelphia:

  • Collect serum (3-8 days after onset) and CSF for patients with unexplained encephalitis or meningitis. Absence of detectable antibodies in serum within 8 days does not exclude possible WNV and samples can be recollected after 8 days if concern continues.
  • Report suspected and confirmed WNV infections (neuroinvasive or non-neuroinvasive illness) and encephalitis cases to PDPH by telephone at 215-685-6741 (or 215-686-4514 after hours).
    • Reports also may be faxed to 215-238-6947.