The Department of Public Health will spray for mosquitoes in three neighborhoods Wednesday night and three other neighborhoods Thursday, all on the Northwest Side. View Full Caption Getty Images

CITY HALL — The Department of Public Health plans a third salvo of spraying on the Northwest Side to attack mosquitoes potentially carrying West Nile Virus.

"When our mosquito traps indicate that the West Nile Virus may threaten human health in a community, we take decisive action," said Health Commissioner Bechara Choucair, M.D. "Even though this summer has been cooler than average, we all must take appropriate precautions."

Before the first spraying Heather Cherone said it's safe, but officials say it might be a good idea to close your windows:

City crews spraying what's reported to be an "ultra-low volume" of the substance Zenivex will target an area including Norwood Park, Portage Park and Dunning on Wednesday in the 36th, 38th and 41st wards. They will follow with additional spraying in Norwood Park and Jefferson Park, Forest Glen and North Park in the 39th, 41st and 45th wards on Thursday. Spraying will take place from dusk to 1 a.m., weather permitting, both days.

Dr. Bechara Choucair, commissioner of public health, said the city has to "take decisive action" against mosquitoes potentially carrying West Nile Virus. View Full Caption DNAinfo/Ted Cox

The city previously sprayed for mosquitoes the last two weeks in August in Norwood Park, Portage Park, Dunning, Montclare, Belmont-Cragin and Austin.

Zenivex "has been used effectively to control disease-carrying mosquitoes and is non-persistent, decomposing rapidly in the environment," according to the city. A city statement on the spraying added, "While the spray is not harmful to people or pets and is routinely sprayed in residential areas across the nation, residents of targeted neighborhoods may choose to stay indoors and close their windows while spraying is underway, as an extra precaution."

"Spraying to kill adult mosquitoes is a sensible and effective component of an integrated pest-management program," added Cort Lohff, the department's environmental health medical director. "It is our expectation that this effort will further limit the mosquito population and prevent cases of human illness in Chicago."

A West Ridge woman in her 70s was confirmed as the city's first West Nile case of the year last month and was reported to be recovering at home.

The department urges residents to eliminate standing water and keep grass mowed and weeds down, as well as wear bug repellent and long pants and long-sleeved shirts to deter bites. It has created a website on preventing transmission and another on West Nile Virus.

For more Northwest Side news from Heather Cherone, listen here: