Illinois Department of Public Health spokeswoman Melaney Arnold says almost 150 people have been admitted to intensive care units with the flu this season and six have died.
Eight Chicago-area hospitals were turning away ambulances Monday night as they dealt with a flood of patients with flu-like symptoms.
U.S. health officials say the strain of influenza virus going around this year has been linked to more hospital admissions and deaths.
"This season is a reminder of how serious flu can be," said Dr. Julie Morita of the Chicago Department of Public Health. The most recent reports from Chicago labs that test for influenza showed 17 percent of specimens tested positive. Last year by this time, fewer than 1 percent of the tests were positive.