Sign of Summer: Mosquitoes in Northfield test positive for West Nile virus

A batch of mosquitoes collected in Northfield on June 5 is the first in the area this year to test positive for the West Nile virus.

Each year, the North Shore Mosquito Abatement District tracks the presence of the West Nile virus throughout its 14 communities, which include Wilmette, Winnetka, Northfield, Kenilworth and Glencoe. Typically, hundreds of batches of mosquitoes test positive each year, including 318 in 2023.

In a press release announcing the positive find, the NSMAD said risk to humans is “low at this time” but provided recommendations for residents to minimize mosquito bites and protect themselves, including:

• Using an EPA-registered insect repellent,

• Wearing loose fitting clothing, and

• Avoiding peak mosquito feeding times during the hours around dawn and dusk.

Additionally, the NSMAD urges residents to eliminate items on their property that hold water, “particularly smaller items that may be easily overlooked.”

“If it can hold water, it can breed mosquitoes!” the district’s release says.

The district sets mosquito traps throughout its coverage area each season. The traps collect a number of mosquitoes and then are collected by NSMAD personnel and tested for the West Nile virus.

So far in 2024, the district has tested 152 batches of mosquitoes with the one in Northfield being the only positive. Positivity rates generally climb later in the summer, according to past data. In 2023, the mosquito abatement district tested 1,158 mosquito samples with 318 of them, or 27 percent, testing positive for West Nile virus. The rates were 26% in 2022 and 32% in 2021.

In 2022, one person — a Wilmette resident — in the abatement district’s coverage area tested positive for West Nile virus. The 10-year average (2013-2022; 2023 data not available) is 3.4 human cases of West Nile virus per summer. There were 20 local human cases in 2012.

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joe coughlin
Joe Coughlin

Joe Coughlin is a co-founder and the editor in chief of The Record. He leads investigative reporting and reports on anything else needed. Joe has been recognized for his investigative reporting and sports reporting, feature writing and photojournalism. Follow Joe on Twitter @joec2319