Since June 26th, 52 mosquito pools infected with West Nile virus (WNV) have been identified in Philadelphia. Positive mosquito pools also have been identified in neighboring counties in Pennsylvania. No human cases have been reported in the City. While the number of human cases of WNV and location of outbreaks has varied by season across the country, identification of mosquitoes infected with WNV remains the best predictor of increased risk for human infection in a given location. The WNV mosquito pool positivity in 2019 is lower than the historic median rate (0.07% vs. 2.2%), and lower than rates observed in 2012 and 2018 (17-36%), peak WNV activity seasons in Philadelphia.

From May through October, the Philadelphia Department of Public Health (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 2019, six locations in Philadelphia were treated 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 weekly report of West Nile Virus in a printable format.

Click here to view travel-related arboviral infections surveillance data.

Click here to download the 2018 season summary report of West Nile Virus in a printable format.

2019 Philadelphia West Nile Virus Mosquito and Human Case Surveillance

Morbidity Week 32 and Cumulative 2019 Season Update:

Week 32 (08/04-08/10) 2019 Season (05/01-08/10)
Mosquito Pools Tested* 55 692
WNV Positive Pools 17 52
Humans Tested** 0 10
Human WNV Cases 0 0
*692 mosquito pools at 108 different mosquito trapping sites
**Testing among case reports received by PDPH only

2019 Geographic Distribution of Positive Mosquito Pools and Human Cases:

Geographic Distribution of Positive Mosquito Pools and Human Cases

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 CSF (from symptom onset—day 8) and serum (day 8—14) from patients with unexplained encephalitis or meningitis for WNV IgM testing.
  • Report suspected and confirmed WNV infections (neuroinvasive or non-neuroinvasive illness) and encephalitis cases to PDPH by telephone at 215-685-6742 (or 215-686-4514 after hours). Reports also may be faxed to 215-238-6947.

State and National West Nile Virus Activity Reports

Updated: 08/16/2019