Chicago has not seen any human cases of West Nile Virus so far this year, and public health officials are spraying for mosquitoes to keep it that way.
"We had a very mild winter, and that started the ball early," said Dr. Dan Markowski of Vector Disease Control International, the company performing the spraying.
Pesticides were sprayed in the 36th ward Wednesday night. The 13th and 23rd wards will be treated Thursday, the department said.
Officials trapped mosquitoes that tested positive for the virus in those three wards, mosquitoes some residents have stayed indoors to avoid.
"I stay inside with the baby," said Yesina DeJesus as she held her daughter's hand. "I don't go out much."
The technicians are using an ultra-low-volume spray called Zenivex. That spray is not harmful to people or pets, though the Department of Public Health recommends that residents in the areas to be sprayed stay inside and keep windows and doors closed.
To prevent mosquito population growth, the city recommends draining and replacing water in birdbaths and wading pools every four days. People should also check gutters, downspouts, and pool covers for water and keep grass and weeds short.
A little more than 700 human cases of the virus were reported in the U.S. last year, of which 34 were fatal.
Though West Nile was found earlier this year in Illinois, five human cases nationwide, with none nationally.