Press Release

September 21 , 2010


West Nile Virus Still a Threat

High infection rates in mosquitoes not seen since 2002

SPRINGFIELD, Ill. – Although we are starting to see cooler temperatures as we head into fall, the Illinois Department of Public Health (IDPH) is receiving reports of very high West Nile virus infection rates in mosquitoes. The infection rate in some areas of northeastern Illinois is currently comparable to 2002 infection rates, when Illinois lead the country in human cases of West Nile virus and deaths.

To date, IDPH is reporting 11 human cases of West Nile virus in Illinois, but fortunately, no deaths. “People need to continue to wear insect repellent when going outside during the evening. The high infection rate of mosquitoes means there is an increased risk for people to contract the disease,” said Illinois Department of Public Health Director Dr. Damon T. Arnold. “We typically see the end of West Nile virus after the first couple hard frosts. Until then, people should continue to protect themselves against mosquito bites.”

So far this year, 28 counties have reported mosquito batches, birds or people testing positive for West Nile virus. The first West Nile virus positive results this year were reported on May 13 and included two birds, one from Carroll County and the other from St. Clair County. The first human case of West Nile virus in Illinois in 2010 was reported August 31 in DuPage County.

In 2009, IDPH reported the first positive mosquito samples on June 1 in Cook County. The Department reported the first human case of West Nile virus in 2009 on August 31. Last year, 36 of the state’s 102 counties reported having a West Nile positive bird, mosquito sample, horse or human case. Five human cases of West Nile disease were reported for 2009.

West Nile virus is transmitted through the bite of a mosquito that has picked up the virus by feeding on an infected bird. Most people with the virus have no clinical symptoms of illness, but some may become ill three to 15 days after the bite of an infected mosquito. The first human case in Illinois is not usually reported until July or later.

Only about two people in 10 who are bitten by an infected mosquito will experience any illness. Illness from West Nile is usually mild and includes fever, headache and body aches, but serious illness, such as encephalitis and meningitis, and death are possible.

Persons older than 50 years of age have the highest risk of severe disease.

The best way to prevent West Nile disease or any other mosquito-borne illness is to reduce the number of mosquitoes around your home and to take personal precautions to avoid mosquito bites. Precautions include:

  • Avoid being outdoors when mosquitoes are most active, especially between dusk and dawn
  • When outdoors, wear shoes and socks, long pants and a long-sleeved shirt, and apply insect repellent that contains DEET, picaridin, oil of lemon eucalyptus or IR 3535, according to label instructions. Consult a physician before using repellents on infants.
  • Make sure doors and windows have tight-fitting screens. Repair or replace screens that have tears or other openings. Try to keep doors and windows shut, especially at night.
  • Eliminate all sources of standing water that can support mosquito breeding, including water in bird baths, ponds, flowerpots, wading pools, old tires and any other receptacles. In communities where there are organized mosquito control programs, contact your municipal government to report areas of stagnant water in roadside ditches, flooded yards and similar locations that may produce mosquitoes.

Public health officials believe that a hot summer increases mosquito activity and the risk of disease from West Nile virus.

Additional information about West Nile virus can be found on the Illinois Department of Public Health’s Web site at

idph online home
idph online home

Illinois Department of Public Health
535 West Jefferson Street
Springfield, Illinois 62761
Phone 217-782-4977
Fax 217-782-3987
TTY 800-547-0466
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