CHICAGO (CBS) — It’s official. In Cook County, this year’s mosquitoes aren’t just nuisance biters anymore. Culex mosquitos, which carry the West Nile virus, are out now.

As CBS 2’s Kristyn Hartman reports, tests out on Wednesday showed Culex mosquitoes have surfaced in Evergreen Park, Glenview, Norridge and Oak Lawn.

Tinley Park resident Linda Armour said the mosquitoes have been “horrible” this year.

As of Thursday, they’ve gotten worse, just because of some test results that came back to the Cook County Department of Public Health.

Its teams have been trapping and testing the blood suckers at 28 different sites.

In Evergreen Park, Glenview, Norridge and Oak Lawn, they found some infected with the West Nile virus.

The Culex mosquito can make you sick if he’s carrying the virus and he bites you.

Dr. Stephen Martin, CEO of the Cook County Department of Public Health, said the agency is “very concerned” about every positive test.

He said that early, heavy summer rain, the recent hot weather and standing, stagnant water make conditions perfect for the Culex mosquito to multiply.

But he also said you can take a bite out of the biters by knowing a few things.

He said mosquitoes only need about a thimbleful of water to breed, so homeowners should “get rid of the standing water, cut the grass.”

Armour said she does both of those things regularly at her home in Tinley Park. Her family also goes inside from dusk to dawn and wear insect repellant.

It’s all to avoid the bite that could become much more serious.

On the county’s website, officials have posted a video of a woman telling the public how she was taken to the emergency room and ended up hospitalized for eight days after she contracted West Nile.

Her recovery is ongoing. She’s among nearly 500 cases in suburban Cook County since 2002. Of those, 27 people died.

It’s why the Department of Public Health wants you to take seriously its message about the prevention measures to keep mosquitoes at bay.