Overview

• Chicago confirmed its first three locally transmitted West Nile virus cases of 2025 in residents aged 40 to 80 with symptom onset in late July and early August.
• Surveillance data revealed an unusually high proportion of Culex mosquito samples testing positive, prompting the city to raise its West Nile risk level to high.
• The Chicago Department of Public Health has scheduled ultra-low-volume truck spraying in multiple community areas at dusk and early evening to reduce adult mosquito populations.
• Officials urge residents to eliminate standing water, wear protective clothing, apply EPA-registered repellents, and avoid outdoor activity during peak mosquito hours at dusk and dawn.
• Illinois recorded its earliest human West Nile virus case since 2016 in late June, leading state and local agencies to intensify weekly mosquito pooling and larvicide treatments across affected counties.