Health officials say statewide flu activity is "regional," which is a step below "widespread." That means the flu has been confirmed in less than half the regions of the state.
In Chicago, hospitals are reporting an increase in emergency room visit from people with flu-like symptoms. But levels are half what they were during the same week last season.
"It's been very quiet, very much in the background," Paul Schreckenberger, microbiologist, said of the strain. "Then all of the sudden this year, starting last week, we've had a big upsurge of the 2009 pandemic strain."
Over the past few weeks, H1N1 was found among patients tested at Loyola University Medical Center and nearly two dozen cases of H1N1 flu virus have been confirmed in the Chicago area in the last week. Scientists at Loyola are using high-tech machines to detect how H1N1 spreads. While doctors say the number of people infected is expected to climb, they also say people should not panic and this year's flu vaccine includes immunizations for the different H1N1 strains.
"We can't just think of the very young and very old as the only ones who need the vaccine. Really, everyone should be vaccinated," Schreckenberger said.
Symptoms of the H1N1 strain are similar to that of the season flu. They include: high temperatures and fatigue; aches and pains; headache, runny nose and sore throat; and vomiting and diarrhea.
In 2009, hundreds of thousands of people worldwide died of the strain.
The Associated Press contributed to this report. All rights reserved.