Naperville residents face a direct West Nile virus threat after mosquito batches collected in the city tested positive as recently as Thursday, Sept. 3.

The finding, drawn from Illinois Department of Public Health data reported by NCTV17, came the same week Will County confirmed its first human case of 2026. The Will County Health Department said a 51-year-old resident developed symptoms in August, was not hospitalized and is now recovering at home.

Naperville straddles both DuPage and Will counties, and both now have confirmed human cases. DuPage County reported its first case around Sept. 1. As of Thursday, Sept. 10, 24 people across Illinois had tested positive for West Nile in 2026. Two had died. Mosquitoes in 52 of the state's 102 counties have carried the virus.

Naperville traps flagged the virus weeks ago

The city's own mosquito monitoring program sounded an early alarm in late July. Traps on Genesee Drive, at Sportsman's Park off West Street and on Olesen Drive all returned positive results during the weeks of July 20 and July 27, according to a city notice published July 31. City crews treated those areas, inspected breeding sites and re-treated nearby catch basins.

Which specific Naperville traps tested positive on Sept. 3 has not been publicly identified. The IDPH data confirms the city-level finding but does not name trap locations.

Who is most at risk

There is no vaccine and no treatment for West Nile. Eight in 10 infected people show no symptoms at all. One in five develop mild, flu-like illness including headache, body aches and rash.

The real danger falls on a smaller group. About one in 150 infected people develop severe illness affecting the central nervous system. Adults 60 and older and those with conditions such as cancer, kidney disease or hypertension face higher risk, according to the CDC.

IDPH Director Dr. Sameer Vohra said in a Sept. 1 news release, when DuPage County announced its first case, that the virus poses the greatest risk to older adults, people with chronic medical conditions and immunocompromised individuals. In the Will County announcement on Sept. 10, Vohra urged caution: "Before heading outside, it's important to take steps to protect yourself and loved ones from mosquito bites and the illnesses they can spread."

What residents can do now

The IDPH advises a three-step approach it calls "fight the bite":

• Reduce standing water around your property and keep doors and windows screened.
• Repel mosquitoes with EPA-approved insect repellent. The city recommends products with 25% to 35% DEET and advises consulting a physician before using repellent on young children.
• Report standing water in public areas to your local health department.

West Nile activity generally drops after the first frost of the season, according to the DuPage County Health Department. DuPage County's Personal Protection Index, which tracks local virus risk on a 0-to-3 scale, was at level 2 (moderate) as of Sept. 1 and is updated every Wednesday at dupagehealth.org.

City Hall week ahead

No Naperville City Council or health-related public hearings specific to West Nile have been announced for the coming week. The DuPage County Health Department updates its Personal Protection Index every Wednesday. Residents can check the current level and mosquito surveillance data at dupagehealth.org.