CDPH Conducts a Comprehensive Mosquito Surveillance and Control Program to Reduce Threat for Residents

July 9, 2021

First West Nile Virus Positive Mosquitoes in Chicago Reported for 2021

Erica Duncan


CHICAGO - The Chicago Department of Public Health (CDPH) has confirmed the first West Nile Virus (WNV)-positive mosquito batches in the City for 2021.  CDPH will continue to monitor the areas where the mosquitos tested positive and will determine the appropriate next steps to be taken following additional tests. No human cases of WNV have been reported to date in 2021.

“As Chicago is reopening, we want to ensure that all Chicago residents can enjoy their summer while remaining safe and healthy,” said CDPH Commissioner Allison Arwady, M.D. “Chicago has one of the most robust mosquito control programs in the country. We remain vigilant about protecting residents against West Nile Virus and will continue our surveillance throughout the season.”

CDPH began its annual mosquito control activities on May 26th. This includes treating 40,000 catch basins in Chicago with larvicide, which kills immature mosquitoes and is the most effective control strategy. In addition, CDPH places up to 83 traps throughout the city and tests mosquito samples every week. This information allows CDPH to respond quickly to reduce risks of mosquitoes through neighborhood outreach and spraying in specific geographic areas. The best way to prevent infection from WNV and other mosquito-borne diseases is to reduce the number of mosquitoes around your home and avoid mosquito bites. Residents are encouraged to take personal precautions against mosquitoes:

  • Use insect repellant that contains DEET, Picaridin, IR3535 or Oil of Lemon Eucalyptus according to label instructions.
  • Eliminate standing water. Empty water from flowerpots, gutters, tires, toys, pet water dishes and birdbaths once weekly.
  • Keep grass and weeds short to eliminate hiding places for adult mosquitoes.
  • When outside between dusk and dawn, wear loose-fitting, light colored clothing, long pants, long-sleeved shirts, socks and shoes.
  • Make sure that all screens, windows and doors are tight fitting and free of holes. Repair or replace screens that have tears or other openings.
  • Check on neighbors regularly, especially those who are older, live alone or need additional assistance.

WNV is typically spread to humans via the bite of infected mosquitoes. Most mosquitoes do not carry the virus. While most people infected with WNV do not feel sick, about 1 in 5 people develop a fever and flu-like symptoms. Severe illness can occur in about 1 in 150 people and is most likely in people over age 60. Because there are no specific medications to treat WNV in people, the most effective method to prevent infection is to prevent mosquito bites.

For more information about mosquito-borne diseases, including symptoms and prevention, visit

Call 311 to report standing water, dead birds or high grass/weeds.



News Release Facts


I Want To