Mosquitoes trapped in Wilmette tested positive for West Nile virus this week, marking the first local detection as temperatures increase.

The North Shore Mosquito Abatement District confirmed that a batch of mosquitoes collected Monday, June 15, from a Wilmette trap tested positive for the virus on Tuesday, June 16. It's the first positive detection in Wilmette this year, though not the first in the district's coverage area. Positive batches were previously found in Evanston on May 26 and Northbrook on June 8.

The district has tested 217 batches of mosquitoes so far this season. Three have come back positive.

Human risk remains "low" on the district's three-tier scale (low, medium, high), according to the NSMAD. The agency determines risk using a "vector index" that combines two factors: the infection rate in trapped mosquitoes and overall mosquito abundance. Last year, the risk level moved to "moderate" mid-summer and stayed there through the season.

The specific threshold that triggers a move from low to medium has not been publicly stated for 2026 as of June 18.

In August 2025, the district recorded a 6.5% infection rate in trapped mosquitoes, the highest in its 20-year testing history. The previous record was 5.9% in 2012, the last outbreak year. Mark Clifton, the district's executive director, attributed the surge partly to heat: "Warm temperatures make everything in the mosquito development process happen faster," he said at the time.

Mid-June is typical for West Nile to first appear in the district's samples, according to NSMAD data. The virus's prevalence tends to climb later in summer, with risk of transmission highest June through October.

The district recommends four protective steps: apply EPA-registered insect repellent, wear loose-fitting clothing, avoid outdoor activity around dusk and dawn, and eliminate standing water on your property where mosquitoes breed.

West Nile virus causes fever, headache, body aches, vomiting, diarrhea, or rash, according to the CDC. Most infections are asymptomatic, but about 1 in 150 infected people develop serious neurological illness that can be fatal. People older than 55 and those with weakened immune systems face the highest risk of severe outcomes.

Residents can track current test results on the NSMAD's Mosquito Surveillance Dashboard at nsmad.org.

North Shore Community & Culture: Coming Up

  • Friday, June 19 – Saturday, June 20 | Winnetka | Downtown Winnetka — Winnetka Music Festival, 10th anniversary. 25+ artists across 4 stages. Tickets required; visit the festival's official site for pricing and availability.
  • Friday, July 3, 9 p.m. | Glencoe | Lakefront Park — Fireworks over Lake Michigan.
  • Saturday, July 4, 1 p.m. | Glencoe | South/Hawthorn to Hazel Ave. — Independence Day Parade, preceded by live music from DJ Pizza Head.