During Morbidity Week 35, the Philadelphia Department of Public Health (PDPH) continued to identify an increased number of mosquito pools infected with West Nile Virus (WNV) throughout the City. The cumulative WNV mosquito pool positivity rate through Week 34 in 2017 is higher than the historic median rate (18% vs. 3%) and slightly lower than rates from 2010 and 2012 (19—23%), peak WNV activity seasons in Philadelphia. No human cases have been reported in the City so far this season; however, identification of mosquitoes infected with WNV remains the best predictor of increased risk for human infection.

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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2016 Philadelphia West Nile Virus Surveillance Update

Cumulative 2017 Surveillance Update Report:

Week 35 (08/27-09/02) 2017 Season (05/01-09/02)
Mosquito Pools Tested 32 1483*
WNV Positive Pools 5 263
Humans Tested** 0 10
Human WNV Cases 0 0
*1483 mosquito pools at 338 different mosquito trapping sites.
**Testing among case reports received by PDPH only

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: 09/13/17 5:00pm