First 2026 human case of West Nile virus reported in DuPage County

The DuPage County Health Department (DCHD) is reporting the first human case of West Nile virus (WNV) in DuPage County in 2026 in an adult resident.

With additional reports of human WNV illness throughout the state, DCHD is encouraging residents to stay safe outdoors by protecting themselves from mosquito bites and the risk of contracting WNV.

WNV is commonly spread to people through the bite of an infected mosquito. Fortunately, most people infected with WNV do not feel sick. About one in five people who contract the disease may develop common symptoms, including fever, headache, body aches, joint pain, or other potentially serious complications.

There are no vaccines to prevent or medicine to treat WNV infection in people, so the best way to prevent WNV is to avoid mosquito bites and follow the 3Rs of defense:

• Reduce the number of mosquitoes by removing containers outside that hold water and making sure doors and windows have tight-fitting screens or keeping them closed.
• Repel mosquitos by using an EPA-registered insect repellent.
• Report areas where water sits for more than a week.

Residents are encouraged to check the Personal Protection Index (PPI) on the Health Department’s website for the most up-to-date information on WNV activity. The current PPI level has been raised to 2, which indicates high numbers of infected mosquitoes in most areas and at least one human WNV case in DuPage County.

The PPI widget is updated by 3 p.m. every Wednesday throughout WNV season. These weekly updates are determined by the Health Department’s vector-borne disease surveillance experts.

WNV activity generally decreases in the fall when cooler temperatures arrive, especially after the first frost of the season. Find additional information at https://www.cdc.gov/west-nile-virus/about/index.html and https://dph.illinois.gov/topics-services/diseases-and-conditions/west-nile-virus.html.