That means many areas in Illinois have confirmed cases, which is typical for this time of year.
So if you are experiencing fever, dry cough and muscle aches, chances are you have one of the influenza strains.
If you're dealing with an upset stomach, doctors say that is another bug altogether. True influenza is what most area hospitals are starting to see.
Emergency room doctors at Northwestern Memorial Hospital say some patients are coming in with more severe symptoms than is typical.
But infectious disease specialist Michael Ison says for the most part, the illness is what they expect.
What is unusual is that more cases of influenza b are being detected; a strain that usually shows up later in the season.
Dr. Michael Ison, an expert in infectious disease at Northwestern, says it's not too late to get the vaccine.
"According to the CDC, the strains that are in circulation currently are very well matched to the vaccine so it should provide excellent efficacy," said Dr Ison. "The other thing you have to recognize is that once you get the flu vaccine is only protecting you against flu and it takes a couple of weeks for that protection to develop so if you get exposed the day after you get the vaccine or you get exposed to another virus that isn't influenza you still may get sick."
Also on Monday, a study from the University of Chicago finds people who got H1N1 or swine flu last year seem to have developed super flu antibodies. And that means they may now be protected against all the seasonal H1N1 strains.
Scientists say this adds to growing evidence that a universal flu vaccine protecting against all flu strains may one day be possible.
