Regular Sign of Summer: Mosquitoes test positive for West Nile in Winnetka, Glencoe, Wilmette

It is that time of the year as the North Shore Mosquito Abatement District recently has collected mosquitos in Winnetka, Glencoe, Wilmette and other local communities that tested positive for West Nile virus.

The positive batches were collected on July 28 (Winnetka), July 26 (Glencoe, Niles and Northbrook) and July 21 (Wilmette).

The district sets mosquito traps throughout its coverage area each season. West-Nile-positive traps are found locally every summer, and the mosquito abatement district is calling the risk to humans “low at this time.”

“While the risk of being infected with West Nile virus is low at this time, it is increasing,” said Dave Zazra, communications manager with the district in a press release. “The NSMAD recommends that residents take personal protection measures to minimize mosquito bites including: using an EPA registered insect repellent, wearing loose fitting clothing and avoiding peak mosquito feeding times during the hours around dawn and dusk.”

Zazra also urged residents to remove items that can hold water, such as bird baths, buckets and “smaller items that may be easily overlooked.

So far in 2023, through July 28, the mosquito abatement district has tested 629 mosquito samples with 37 of them, or 5.9 percent, testing positive for West Nile virus. Through mid-July in 2022, the positivity rate was around 2 percent.

The positivity rate annually climbs as the summer turns to fall. The most prolific months of West Nile spread are typically August and September. Last year’s final positivity rate was 26 percent (456 of 1,738 traps), and in the past few years, overall positivity ranges from 21% to 31%.

No human cases have been identified in the district yet in 2023. Last year, one person — a Wilmette resident — in the abatement district’s coverage area, which encompasses 14 communities, tested positive for West Nile virus. The 10-year average (2013-2022) is 3.4 human cases of West Nile virus per summer. There were 20 local human cases in 2012.

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