Despite cooler fall temperatures, West Nile Virus numbers aren't expected to drop in the near future.
That's because there are still infected mosquitos in the air, and if bitten, people could become ill in two-to-three weeks, said Sean McDermott, spokesman for the Cook County Department of Public Health.
It takes three to 15 days for West Nile to start showing symptoms in a victim, said Amy Poore, director of public relations for Cook County Health Department.
Poore said testing is a process, so there is a substantial timeline in the reporting of positive cases. People who are suspected to be infected must first pass the Centers for Disease Control case definition, and then laboratory confirmed testing at the Illinois Department of Public Health.
"We've definitely seen our peak for the season, but testing continues. There has been a major decline in [West Nile Virus] exposed mosquitos, but with days at 70 degrees outside this fall, people still must be vigilant," Poore said.
To date, six people have died in Illinois out of the 179 West Nile Virus cases reported. Those infected range in age from children not yet one-year-of-age to 84-year-olds, according to the Illinois Department of Public Health website.
Cases of West Nile Virus have more than quadrupled compared to 2011 when there were 34 cases.
Northern Illinois counties where positive test results for West Nile Virus have been found include Cook, Lake, DuPage, Will, Kane McHenry, Winnebego, Dekalb and Kankakee.
Five counties in central and southern Illinois, Peoria, McLean, Macoupin, Bond and Crafword, also have been identified as positive human test areas by the state health department.
Throughout the U.S. 3,969 cases have been reported this year, which is the highest number of West Nile Virus cases since 2003.