First West Nile Virus-Positive Mosquitoes in Chicago Reported for 2026

CDPH Conducts a Comprehensive Mosquito Surveillance and Control Program to Reduce Threat for Residents

CHICAGO - The Chicago Department of Public Health (CDPH) has confirmed the first West Nile virus (WNV)-positive mosquitoes in Chicago in 2026. The Illinois Department of Public Health previously reported the first mosquitoes to test positive for WNV in the state on May 14, 2026. No human cases of WNV have been reported in Illinois this year.

CDPH has a robust program to prevent and control WNV, which includes treating over 80,000 catch basins with larvicide to prevent adult mosquitoes, collecting and testing mosquitoes every week for WNV, spraying to kill adult mosquitoes in specific areas if indicated, and monitoring human WNV infections.

"One of the best ways for Chicagoans to have a safe and healthy summer is by protecting themselves from mosquito bites," said CDPH Medical Director Dr. Janna Kerins.

Chicagoans can prevent mosquito bites by:

• Using EPA-registered insect repellent according to label instructions, especially when applying to children.
• Wearing long-sleeved shirts and pants when outside between dusk and dawn.
• Controlling mosquitoes indoors by making sure that window and door screens do not have holes and by using air conditioning if possible.
• Controlling mosquitoes outdoors by keeping grass and weeds short to eliminate hiding places for mosquitoes and emptying items that hold water like flowerpots or birdbaths once weekly.
• Checking on neighbors regularly, especially those who are older, live alone or need additional assistance.

WNV is typically spread to humans via the bite of infected mosquitoes. Most mosquitoes do not carry the virus. While most people infected with WNV do not feel sick, about 1 in 5 people develop a fever and flu-like symptoms. Severe illness can occur in about 1 in 150 people and is most likely in people over age 55 or who have weakened immune systems. Because there are no specific medications to treat WNV in people, the best way to keep yourself from getting sick is to prevent mosquito bites.

For more information about mosquito-borne diseases, including symptoms and prevention, visit https://www.chicago.gov/health. To report standing water, dead birds or high grass/weeds, call 311.

The Chicago Department of Public Health works with communities and partners to create an equitable, safe, resilient and Healthy Chicago.

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