SPRINGFIELD, IL – With the addition today of 10 more laboratory positive cases of West Nile disease, this year's epidemic has now surpassed Illinois' last major outbreak of mosquito-transmitted disease in 1975 in number of cases and is the largest since the early 1900s when the state was battling malaria.

Twenty-seven years ago, Illinois counted 578 human cases of St. Louis encephalitis and 47 deaths; both figures represented the highest totals in the United States. In 2002, Illinois leads the nation with 583 cases of West Nile illness as of today and 32 deaths. The West Nile outbreak is the largest caused by mosquitoes since 1917 when there were 2,300 cases of malaria.

"We don't know the answer to why Illinois has been so adversely impacted by West Nile virus infection this year," said. Dr. John R. Lumpkin, state public health director. "It is something we will continue to study this year, next year and, most likely, for years to come."

Dr. Lumpkin said there are similarities between the 1975 and 2002 outbreaks, including like weather patterns – wet springs, followed by dry, hot summers with a number of days with temperatures at 90 degrees and above, which are ideal for mosquito breeding – and a clustering of cases in two areas of Cook County. As was the experience in 1975 in Cook County, the suburbs of Skokie, Morton Grove and Evanston and the north side of Chicago and the southwestern neighborhoods of Chicago, Oak Lawn, Evergreen Park and other surrounding suburbs have seen a majority of the Chicago area cases. Dr. Lumpkin has requested federal assistance to study why those two areas have been particularly hard hit in both 1975 and 2002.

If 1975 and 2002 prove to be comparable, one optimistic point may emerge, Dr. Lumpkin said, noting that, after the nearly 600 cases of St. Louis encephalitis in 1975, the next year there were just 19 cases.

"We will prepare as if next year will be equally severe but, historically in the United States, a year of high numbers of mosquito-borne disease in a particular area is often followed by a sizable drop in cases," Dr. Lumpkin said. "We hope that will be the experience in Illinois in 2003."

The 10 new cases of West Nile disease reported today include five from the city of Chicago, one from suburban Cook County, and one each from DuPage, Madison, Macoupin and Montgomery counties. The 583 human cases have been identified in 41 of the state's 102 counties; they range in age from 3 months to 97 years. The average age is 56.

The state's 32 fatalities this year from West Nile encephalitis have been from Chicago (7), suburban Cook County (15) and one each from DuPage, Effingham, Fulton, Knox, Lake, Macon, Madison, Moultrie, Sangamon and White counties.

Cases announced today follow:

CHICAGO: A 44-year-old man, whose hospital information is not known; a 50-year-old man, whose hospital information is not known; a 48-year-old man, whose hospital information is not known; an age unknown man, who was not hospitalized; and a 43-year-old man, who was not hospitalized.

SUBURBAN (SOUTHERN) COOK COUNTY: A 28-year-old woman, who was hospitalized with West Nile encephalitis.

DUPAGE COUNTY: A 73-year-old woman, whose hospital information is not known.

MADISON COUNTY: A 49-year-old man with West Nile encephalitis, whose hospital information is not known.

MACOUPIN COUNTY: An 81-year-old man, who was hospitalized with West Nile encephalitis.

MONTGOMERY COUNTY: A 43-year-old man, who was hospitalized with West Nile encephalitis.

A complete listing of the positive birds, mosquito batches, horses and humans identified so far in Illinois, by county, is available on the Department's Web site at <www.idph.state.il.us>. Go to the West Nile virus page and select "2002" under surveillance.

Dr. Lumpkin reminded Illinoisans it was still important to take the following steps to reduce the chance of mosquito bites until their area experiences a hard frost:

• Avoid being outdoors at dawn, dusk and early evening when mosquitoes are most active. If outdoors at these times, wear shoes and socks, long pants and a long-sleeved shirt to cover as much of the skin as possible. Loose-fitting, light colored clothing is best.
• Use insect/mosquito repellent containing 25 percent to 35 percent DEET when outdoors when mosquitoes are biting, applied sparingly to exposed skin or clothing, as indicated on the repellent label. Consult a physician before using repellents on young children.
• Check for and repair any holes or tears in residential screens, including porches and patios.
• Eliminate stagnant water in bird baths, ponds, flower pots, wading pools, old tires and any other receptacles in which mosquitoes might breed.

The Culex or house mosquito, which can carry West Nile virus or St. Louis encephalitis virus, breeds in warm, stagnant water and remains active and biting until there is a hard frost. As the temperatures dip below 60 degrees at night and in early morning, the mosquitoes' feeding habits change from seeking blood meals, which they use for reproduction, to sugar meals from plants that help sustain them over winter.

Dr. Lumpkin said most people who get infected with West Nile virus have either no symptoms or mild symptoms, but a few individuals may develop a more severe form of the disease, such as encephalitis or meningitis.

Most people infected with West Nile virus have no clinical symptoms of illness, but some may become ill three to 14 days after the bite of an infected mosquito. Infections can be mild and include fever, headache and body aches, or severe and marked by headache, high fever, neck stiffness, stupor, convulsions, muscle weakness, paralysis and, rarely, death. Serious West Nile virus illness is most often present in individuals 50 years of age or older.

A total of 513 birds, 528 mosquito batches and 431 horses in 98 Illinois counties have tested positive this year for the virus since surveillance for the mosquito-transmitted virus began on May 1.

2002 West Nile virus surveillance information can be found on the Department's Web site at www.idph.state.il.us/envhealth/wnvsurveillance_data02.htm.