An adult DuPage County resident has tested positive for West Nile virus, marking the county's first confirmed human case of 2026.
The DuPage County Health Department (DCHD) announced the case Tuesday, Sept. 1, but did not release the patient's age, city of residence or health status. Elmhurst's mosquito-control season with contractor Clarke is active through Oct. 15, and the elevated risk level applies countywide.
The confirmation came the same day Chicago health officials reported the city's first two human cases and first West Nile death of the year, according to ABC 7.
DCHD raised its Personal Protection Index (PPI) to level 2, or "moderate," on a scale of 0 to 3. The index had been at level 1 since May, when the first mosquito batches tested positive for the virus in Roselle, Glendale Heights and Wheaton.
The higher rating reflects both the human case and a growing number of infected mosquitoes trapped across the county, NCTV17 reported. Illinois Department of Public Health Director Dr. Sameer Vohra said in a statement, as reported by NCTV17, that the virus "can lead to severe illness in high-risk groups such as older adults, individuals with chronic medical conditions, and immunocompromised persons."
About one in five people infected with West Nile develops flu-like symptoms including headaches, body aches, fever and nausea. Less than 1% develop severe symptoms affecting the central nervous system.
The virus is spreading across the region. Cook County had reported four human cases as of Aug. 28, according to Patch. Illinois' first human case of 2026 was confirmed in Piatt County the week before Sept. 1. Statewide, officials recorded 150 confirmed human cases in 2025, more than double the 69 reported in 2024.
What Elmhurst-area residents can do
DCHD recommends its "3 Rs": reduce mosquitoes by eliminating standing water and checking window screens, repel them with EPA-registered repellent, and report public spots where water has pooled for more than a week.
The City of Elmhurst partners with Clarke Mosquito Control for treatments that run through Oct. 15. Adult mosquito spraying takes place between dusk and dawn. Residents can sign up for advance spray notifications at ClarkePortal.com/Hotline or call Clarke's Mosquito Hotline at 1-800-942-2555.
In Villa Park, heavy rainfall and warm weather in July triggered multiple large hatches of floodwater mosquitoes, prompting additional adult mosquito applications.
DCHD updates the PPI every Wednesday by 3 p.m. at dupagehealth.org. The next update is scheduled for Wednesday, Sept. 9.
