After West Nile virus struck Illinois — and particularly Cook County — in the summer of 2002, state and local authorities have seen a significant drop off in cases so far this year.

Only 18 Illinois residents, including six from Cook County, were diagnosed with West Nile this summer, according to the Illinois Department of Public Health.

Last year 884 human cases were confirmed in Illinois, the highest of any state. Almost half of those cases were in suburban Cook County.

By Sept. 22, 2002, 236 cases had been confirmed in Cook County suburbs alone, compared to four cases at the same point this summer.

However, all four human cases in Cook County suburbs in 2003 occurred in the past two weeks, according to the health department. A 38-year-old woman, a 74-year-old woman, a 49-year-old man and a 24-year-old woman from Cook County suburbs all were diagnosed with West Nile between Sept. 9 and Thursday.

Also during this summer, a 45-year-old Evanston woman was diagnosed with eastern equine encephalitis, another mosquito-borne disease. The Illinois Department of Public Health diagnosed the woman July 14 after she complained of a severe headache and stiff neck. She later recovered without complications.

The woman’s diagnosis represented the first case of eastern equine encephalitis in Illinois history, said Jay Terry, Evanston’s director of health and human services. However, Terry said there was little cause for worry in Evanston because the city already was spraying for mosquitoes.

“We already are at a period in our community where we are vigilant in controlling our mosquito problems,” Terry said.

The North Shore Mosquito Abatement District has been spraying for mosquitoes and testing dead birds throughout the summer in Evanston, as well as in other northern suburbs. Community members who want to report suspicious dead birds or standing water should call the mosquito abatement district at 847-446-9434.

The Daily’s Malavika Jagannathan and Elaine Helm contributed to this report.