The Chicago Department of Public Health confirmed the first death from West Nile virus in Illinois this year on September 1, alongside the city’s first two confirmed human cases of the mosquito-borne disease. CDPH did not release identifying details about the person who died. The announcement follows one of the wettest summers Chicago has recorded in years, a weather pattern that public health officials say has created widespread conditions for mosquito breeding across all five sides of the city.
Key Takeaways
- One person in Chicago has died from West Nile virus, the first fatality in Illinois in 2026; CDPH also confirmed the city’s first two human cases
- Midway Airport recorded more than 20 inches of rainfall between June 1 and early August, well above the roughly 13-inch average for that period
- CDPH has sprayed insecticide across 15 community areas over recent weeks and treats more than 80,000 catch basins citywide with larvicide
- Cook County’s Department of Public Health reported the season’s first four suburban cases the previous week; a Piatt County resident was the state’s first confirmed case
- Illinois reported 150 human cases and 10 deaths from West Nile virus in 2025
- The CDC has recorded 407 human cases across 40 states nationally so far in 2026, including 285 neuroinvasive cases
Record Summer Rainfall Has Expanded Mosquito Habitat Across Chicago
CDPH Commissioner Dr. Garth Walker tied the timing and severity of this year’s West Nile cases directly to weather conditions. Chicago’s Southwest Side gauge at Midway Airport logged more than 20 inches of rainfall between June 1 and early August. The typical accumulation for that same period is approximately 13 inches. The surplus has left standing water in catch basins, residential yards, construction sites, vacant lots, and drainage-poor corridors across the city, creating the stagnant conditions that Culex mosquitoes, the primary carriers of West Nile virus, require to breed.
The rainfall data tracks with what Chicago residents have been experiencing at street level. WTTW reported on August 31 that Chicagoans are seeing increased mosquito and tick activity this summer in connection with the persistent storms. The convergence of above-average precipitation and sustained warm overnight temperatures through August has extended the window in which mosquito populations can reproduce. Public health officials have noted that nighttime temperatures remaining elevated means the breeding cycle has not yet been interrupted by the kind of cool-down that typically slows mosquito activity heading into fall.
The City Has Sprayed Insecticide Across 15 Community Areas
In the weeks leading up to the September 1 announcement, CDPH deployed insecticide spraying operations targeting adult mosquito populations in 15 community areas. The affected neighborhoods span much of the South and West Sides, along with one Far Northwest Side community area. Spraying has been conducted in Beverly, Burnside, Chatham, East Garfield Park, Lower West Side, Morgan Park, Near West Side, North Lawndale, O’Hare, Pullman, Roseland, South Deering, Washington Heights, West Lawn, and West Pullman.
The city’s mosquito control program also operates a larvicide treatment system that covers more than 80,000 catch basins across Chicago. Larvicide targets immature mosquitoes before they reach the adult stage, reducing the overall population in areas where standing water collects in storm drains and street-level infrastructure. The dual approach of larvicide treatment and targeted adult spraying reflects a strategy designed to address both the breeding pipeline and the active mosquito population simultaneously.
West Nile Virus Cases Are Emerging Across the Region and the Country
Chicago’s cases are part of a broader pattern. The Cook County Department of Public Health reported the season’s first four human cases in suburban Cook County the week before the city’s announcement. A Piatt County resident, located in central Illinois, was confirmed as the state’s first human case of the year before the Chicago cases were identified.
Nationally, the Centers for Disease Control and Prevention had recorded 407 human cases of West Nile virus across 40 states as of the September 1 reporting period. Of those, 285 were classified as neuroinvasive, meaning the virus had affected the brain or spinal cord. More than 130 deaths had been reported nationally.
Illinois has historically been among the states with higher West Nile virus activity. In 2025, the state recorded 150 human cases and 10 deaths. The 2026 season started later than last year’s but is now accelerating as mosquito populations remain elevated heading into the weeks before the first hard frost, which typically arrives in Chicago in mid to late October.
Most Infections Produce No Symptoms, but Severe Cases Can Be Fatal
West Nile virus is transmitted to humans through the bite of an infected mosquito. The disease does not spread from person to person. According to the CDC, approximately 80% of people infected with the virus experience no symptoms at all. About one in five develop a fever and flu-like symptoms, including headache, body aches, joint pain, vomiting, diarrhea, or rash, typically appearing three to 15 days after infection.
In rare cases, the virus causes severe neuroinvasive illness. Symptoms of severe infection include high fever, stiff neck, disorientation, muscle weakness, tremors, and inflammation of the brain. These cases can result in permanent neurological damage or death. Older adults, individuals with chronic medical conditions, and immunocompromised persons face the highest risk of developing severe illness.
Illinois Department of Public Health Director Dr. Sameer Vohra described the year’s first death as a reminder that West Nile virus should be taken seriously, particularly by people in higher-risk categories. There are no specific antiviral medications or vaccines available to treat or prevent West Nile virus in humans. Prevention remains entirely focused on reducing exposure to mosquito bites.
Public Health Officials Are Urging Chicagoans to Take Precautions Through the Fall
CDPH is advising Chicago residents to take protective measures that target both personal exposure and the conditions that allow mosquitoes to breed near homes. The department’s recommendations include wearing long sleeves and pants during peak mosquito hours around dusk and dawn, applying EPA-approved insect repellent, ensuring that window and door screens are intact, and eliminating standing water from containers around the home, including flowerpots, gutters, pet dishes, and birdbaths.
Residents can report areas of stagnant water where mosquitoes may be breeding to 311 or the Chicago Department of Public Health. The city’s mosquito surveillance and control operations will continue through the fall until sustained cold weather ends the breeding season. Historically, West Nile virus transmission in the Chicago area does not subside until the first hard frost kills off the adult mosquito population, a threshold that typically falls in the second half of October.
