Chicago Department of Public Health

Transforming the health of our city


JULY 18, 2012 



Contact: Efrat Stein 

(312) 747-9805


City to Spray Insecticide Tonight and Thursday
To Kill Mosquitoes
Targeted Effort Fights West Nile Virus in Austin, Clearing, West Lawn and Archer Heights

The City of Chicago Department of Public Health (CDPH) is continuing their efforts against West Nile Virus by spraying to kill adult mosquitoes in portions of Austin, Clearing, West Lawn and Archer Heights.


Spraying will occur in sections of the 36th Ward tonight and in sections of the 23rd and 13th Wards on Thursday.  In all of these locations CDPH traps recently yielded mosquitoes carrying West Nile Virus.


There are three relatively small areas to be sprayed. Download spray zone maps of the 36th ward here and the 23rd and 13th wards here. 


"When our mosquito traps indicate that the West Nile Virus may threaten human health in a community, we take decisive action promptly," stated Chicago Department of Public Health (CDPH) Commissioner Bechara Choucair, M.D.


Weather permitting, the spraying will begin at about 8:00 p.m. on both Wednesday July 18 , 2012 and on Thursday July 19, 2012. On both nights, spraying will continue through the night until approximately 1:00am, with licensed mosquito abatement technicians in trucks dispensing an ultra-low-volume spray.


Spraying will occur starting at dusk, the peak period of mosquito activity and exposure of the Northern House Mosquito, the type of insect that spreads West Nile Virus.


The material being used to control the adult mosquitoes, Zenivex, will be applied at a rate of 1.5 fluid ounces per acre. It is approved for use by the U.S. Environmental Protection Agency and is used to control mosquitoes in outdoor residential and recreational areas.


Zenivex is a synthetic pyrethroid product. Zenivex has been used effectively to control disease-carrying mosquitoes and is non-persistent, decomposing rapidly in the environment. This rapid degradation of this product makes it an excellent choice for control of WNV-carrying mosquitoes.


The spray will be applied by technicians from Vector Disease Control International a leader in the mosquito control industry. Guiding the crews through the streets will be supervisors from the Chicago Department of Streets and Sanitation.


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. We spray when we have clear evidence that the West Nile Virus has made significant inroads into a community," added CDPH Environmental Health Medical Director Cort Lohff, M.D. "It is our expectation that this effort, by further limiting the mosquito population, will prevent cases of human illness in Chicago."


The Northern House mosquito, Culex pipiens, is the primary carrier of West Nile virus. This mosquito species thrives in water with high organic content, such as that found in catch basins (storm sewers). Consequently, a hot, dry summer increases the risk of West Nile virus infection, exactly the opposite of what many people believe.


In contrast, the swarms of mosquitoes most people currently are experiencing are Aedes vexans, which is a common "floodwater" mosquito that appears after heavy rains. This mosquito may be a nuisance, but they rarely are infected with West Nile Virus.


In 2011, some 712 human cases (43 of them fatal) of West Nile-related illness were reported nationally. In Illinois, there were 34 reported cases (8 of them in Chicago) and no deaths.


Thus far in 2012, some 5 cases (0 fatal) have been reported nationally. In Illinois, 0 human cases have been reported.


Additionally, the virus has been detected (in mosquitoes and/or birds) in 19 counties in Illinois, including city and suburban Cook, DuPage, La Salle , Kendall and Will.


Therefore, CDPH officials ask all Chicagoans to take precautions to protect themselves and their families from mosquito bites. Especially important is the use of insect repellant containing DEET, Picaridin, or Oil of Lemon Eucalyptus.

Northern House mosquitoes are not aggressive, and people rarely notice when being bitten.


In addition to using insect repellant to avoid bites, CDPH  officials advise:

  • Consider limiting outdoor activity after dark (dusk to dawn), which is when Northern House Mosquito is most active.
  • When outside between dusk and dawn, wear loose-fitting, light-colored clothing that includes long pants, long-sleeved shirts, socks and shoes.
  • Check to see that all screen on doors and windows are tight-fitting and free of holes and tears.
  • Encourage neighbors to exercise precautions.

To limit mosquito breeding opportunities, CDPH officials recommend:

  • draining and replacing water in birdbaths and children's backyard wading pools every four to five days;
  • properly disposing of old tires, jars, cans, pans, bottles, buckets and other unwanted containers that can hold standing water;
  • making sure that rain gutters, downspouts, swimming pools and pool covers are free of standing water;
  • keeping grass and weeds cut short to eliminate hiding places for adult mosquitoes

Human infections occur when people are bitten by a mosquito carrying the virus. On average, only about 2 in 10 people who are bitten by an infected mosquito will actually become ill.


For those who do become ill, West Nile Virus infection can cause a relatively mild illness called West Nile Fever, characterized by fever, muscle aches, rash and headache. More severe West Nile illness is less common, but can include meningitis (inflammation of the membrane surrounding the brain) and encephalitis (inflammation and swelling of the brain itself). People of all ages are susceptible to West Nile infection, but people over age 50 are at greater risk of developing severe illness.


For prevention tips and updates on West Nile Virus activity in Chicago, visit 


For an expert national perspective on West Nile Virus, visit the Centers for Disease Control and Prevention (CDC) on the Internet at

West Nile Disease, Reported Cases in Chicago:


2002      225 cases, 22 fatalities

2003      4 cases, 0 fatalities

2004      6 cases, 1 fatality

2005      41 cases, 1 fatality

2006      29 cases, 1 fatality

2007      11 cases, 0 fatalities

2008      4 cases, 0 fatalities

2009      1 case, 0 fatalities

2010      1 case, 0 fatalities

2011      8 cases, 0 fatalities


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The Chicago Department of Public Health (CDPH) works to make Chicago a safer and healthier place by working with community partners to promote health, prevent disease, reduce environmental hazards and ensure access to health care for all Chicagoans. Visit us at to learn more about how CDPH is transforming the health of our city.  


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