In 2019, three human West Nile Virus (WNV) infections occurred in Philadelphia. All three infections were neuroinvasive and required hospitalization. The first case of the season was a 59 year-old who had been experiencing homelessness during their entire exposure period and spent most of their time outdoors. The second case was a 61 year-old who regularly spent time gardening outside their home and recalled being bitten by mosquitoes. The last case was a 57-year old resident with a history of lymphoma who spent the majority of their exposure period in Greece and was bitten by mosquitoes while abroad. All three cases underwent rehabilitation and were successfully recovering at the time of the final interview. 

From May through October, the Philadelphia Department of Public Health (PDPH) in collaboration with the PA Department of Environmental Protection conducted mosquito management activities throughout Philadelphia, which entailed surveillance and identification of mosquito pools, testing pools for WNV, and control activities (eliminating breeding sites, larviciding catch basins, ground spraying, etc.) at 13 locations in Philadelphia. The WNV mosquito pool positivity for 2019 was higher than the historic median rate (12.3% vs. 4.2%), and lower than rates observed in 2010 and 2018 (24.3-39%), peak WNV activity seasons in Philadelphia.


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 2019 season summary report of West Nile Virus in a printable format.

2019 Philadelphia West Nile Virus Mosquito and Human Case Surveillance

Cumulative 2019 Season Update:

2019 Season (05/01-10/31)
Mosquito Pools Tested* 1045
WNV Positive Pools 129
Humans Tested** 15
Human WNV Cases 3
*1045 mosquito pools at 151 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: 01/06/2020