So far this season, three human West Nile Virus (WNV) cases have occurred in Philadelphia. Two were adults >50 years of age with neuroinvasive infection that required hospitalization. The other case was a viremic blood donor who developed WNV fever symptoms following the donation. The cumulative WNV mosquito pool positivity rate in 2017 was higher than the historic median rate (17% vs. 3%) and slightly lower than rates from 2010 and 2012 (19—24%), peak WNV activity seasons in Philadelphia. WNV activity in mosquitoes and risk for human infection will continue until the first hard frost occurs.  

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 June 2017, 12 locations across Philadelphia with WNV positive mosquito pools or high numbers of nuisance mosquitoes were treated to control adult mosquito populations.

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2017 Philadelphia West Nile Virus Surveillance Update

Cumulative 2017 Surveillance Update Report:

Week 43 (10/22-10/28) 2017 Season (05/01-10/28)
Mosquito Pools Tested - 1847*
WNV Positive Pools - 316
Humans Tested** 1 18
Human WNV Cases 0 3
   Neuroinvasive WNV 0 2
   WNV Fever 0 1
   Viremic Blood Donor*** 0 1
*1847 mosquito pools at 393 different mosquito trapping sites.
**Testing among case reports received by PDPH only
***1 Viremic donor became symptomativ and is also a WNV Fever case

2017 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 Requirement:

  • 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:11/04/17 6:00pm