The first three human cases of West Nile virus this season in Chicago were reported Tuesday.
The patients range in age from 40 to 80 years old and live on the Northwest and South Sides. Their symptoms began in late July or early August, the Chicago Department of Public Health said.
Though they are the first cases of the virus reported in Chicago in 2025, three other people have contracted West Nile this year in Illinois, according to the Illinois Department of Public Health. Those cases were reported in DuPage, Lake and downstate Wayne counties.
West Nile virus is typically spread through bites from infected mosquitoes, though most mosquitoes do not carry the virus, health officials said.
About 20% of people infected with the virus will experience a fever and flu-like symptoms. And one in every 150 people who get the virus could develop severe illness, with people over 60 more at risk, the health department said.
Several batches of mosquitoes tested positive for West Nile virus in June in at least 16 counties across the state, including Cook County, health officials previously reported.
“We are seeing a higher proportion of mosquitoes testing positive for West Nile virus than usual this year,” CDPH Commissioner Olusimbo ‘Simbo’ Ige said in a statement. “The best way to protect yourself from West Nile virus is to avoid mosquito bites and take measures to stop them from breeding around your home.”
West Nile virus risk is currently rated as high in Chicago, the health department noted.
Health officials have sprayed insecticide in nine community areas across the city in recent weeks, and more spraying is planned for Wednesday and Thursday, the health department said.
The city manages more than 80,000 basins citywide to contain the mosquito population and control the spread of West Nile virus. Officials are also testing mosquitoes weekly until October, according to the health department.
Last year, Illinois had nearly 70 human cases of the virus, down from 119 in 2023 and below the state’s average of about 161 cases per year since 2002. About two dozen people died of the virus statewide last year.
In 2024, suburban Cook County had 19 West Nile virus cases and five deaths from the virus — marking the highest number of county deaths due to the disease since 2018, according to Cook County Department of Public Health data.
Residents can take various approaches to keep mosquitoes away and avoid West Nile virus. The health department encourages residents to take the following precautions:
- Use EPA-registered insect repellent that contains ingredients such as DEET, picaridin, IR3535, or oil of lemon eucalyptus according to label instructions.
- Eliminate standing water: empty water from any outdoor containers, such as flowerpots, gutters, pet water dishes, and birdbaths on a weekly basis.
- Keep grass and weeds short to eliminate hiding places for adult mosquitoes.
- When outside between dusk and dawn, wear loose-fitting, light-colored clothing, long sleeves, pants, socks, and shoes.
- Make sure that all screens, windows, and doors are tight-fitting and free of holes.
- People who are immunocompromised should consider avoiding outdoor activity during peak mosquito hours from dusk to dawn.