Four adults in suburban Cook County have tested positive for West Nile virus, the first confirmed human cases of the 2026 season.
The Cook County Department of Public Health (CCDPH) announced the cases Friday, Aug. 28, and classified the risk of human infection across suburban Cook County as high based on data through the week ending Aug. 22. The high-risk classification covers all of suburban Cook County, including Park Ridge and Niles. The department did not release the towns where the four patients live.
Dr. Kiran Joshi, CCDPH's chief operating officer, urged residents to act before the Labor Day weekend.
"In light of high West Nile virus activity in Cook County, it is incredibly important for people to protect themselves from mosquito bites," Joshi said in the department's statement.
The virus spreads when mosquitoes bite infected birds and then bite people. Most who contract it show no symptoms. Others develop fever, headache, rash and body aches three to 15 days after infection. In severe cases, the virus can attack the brain or spinal cord, causing high fever, confusion, muscle weakness and, in some cases, death.
Suburban Cook County recorded 44 West Nile cases and four deaths in 2025, according to the health department. Statewide, Illinois confirmed 150 human cases in 2025, more than double the 69 reported in 2024.
The Illinois Department of Public Health reported the state's first human case of the 2026 season on Wednesday, Aug. 26, in a Piatt County resident, according to WGN-TV. West Nile virus had already been detected in mosquitoes collected in Northbrook and in DuPage and McHenry counties before the human cases were announced, Patch reported.
How to reduce your risk
The CCDPH's annual "Fight the Bite" campaign recommends four steps:
- Use insect repellent. Adults should apply products containing 20% to 50% DEET. For children, repellents with 20% to 30% DEET are recommended.
- Dump standing water. Empty flowerpots, old tires, buckets, birdbaths and plastic wading pools where mosquitoes breed.
- Fix screens. Repair damaged window and door screens and check for holes or gaps.
- Limit dawn and dusk exposure. Mosquito activity peaks during those hours.
No Park Ridge- or Niles-specific case data has been released. The North Shore Mosquito Abatement District serves the Park Ridge area, but no local trap results from the current season were available as of publication.
Residents can monitor weekly risk updates on the Cook County Department of Public Health website and find prevention resources through the Fight the Bite Cook County campaign.
