Health Information Portal (HIP)

Introduction

Mosquito pools infected with West Nile virus (WNV) continue to be identified across Philadelphia. During MMWR Week 31, an asymptomatic presumptive viremic donor reporting local mosquito exposures was identified. The WNV pool positivity in 2026 is higher than the year-to-date historic median rate from 2001-2025 (22% vs 7%) and similar to rates observed in 2010, 2018, and 2022 (16%-41%), peak WNV activity seasons in Philadelphia. 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 2026, 110 mosquito larvicide treatment events have been conducted across Philadelphia, and six locations 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 2026 West Nile Virus report in a printable format.

West Nile Virus Mosquito and Human Case Surveillance, Philadelphia PA, Morbidity Week 31 and Cumulative 2026 Season Update

^346 mosquito pools at 75 different mosquito trapping sites

State and National WNV Activity Reports

• Pennsylvania Department of Health
• Centers for Disease Control and Prevention

Advise your patients to:

• Use insect repellent that contains DEET (≥20% to also prevent tick bites) or another EPA-approved repellent and reapply as directed.
• 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 to PDPH’s Mosquito Complaint hotline at 215-685-9000. Report sick, injured, or dead wild bird or mammal sightings to the PA Game Commission by calling 1-833-PGC-WILD (742-9453) or emailing pgc-wildlifehealth@pa.gov.

WNV Testing and Reporting Requirements for Human Surveillance in Philadelphia:

• Collect serum and CSF for patients with unexplained encephalitis or meningitis. Absence of detectable antibodies in serum within 8 days does not exclude possible WNV.
• Report suspected and confirmed WNV infections and encephalitis cases to PDPH by telephone at 215-685-6741 during business hours or 215-686-4514 (press 1 for Unified Dispatch and ask for DDC on-call staff) after-hours, or fax at 215-238-6947.