It's spreading across the US and now more cases are being reported right here in Wisconsin.
It's the flu and the type of people getting sick is changing along with this year's most prevalent strain H1N1.
So far, young and middle aged adults have accounted for a majority of hospitalizations in Northeast Wisconsin.
According to an analysis released this week by the group Trust for America's Health" only one in three adults between the age of 18 to 64 were vaccinated last season which ranks Wisconsin 47th in the nation.
Wisconsin is also one of only three states to report a decline in vaccinations in that age bracket.
Winnebago County Public Health Nurse Denise Krueger said, "Normally with influenza we see very young and very old that get sick, and sometimes end up in the hospital. The unusual part this year is it's that middle age group, 20s to 40s that are getting hit and hit pretty hard."
In Winnebago County, several people so far have been hospitalized with flu like symptoms.
It's the same story in Fond du Lac county, although they've also been able to track confirmed cases at about 70.
"I would not say that it's worse and I wouldn't say that more people are getting sick this year compared to last year. It's just that the type of people that are getting sick is so much different than last year," said Kim Mueller, of the Fond du Lac County Health Department.
According the CDC the H1N1 strain which first appeared in 2009 and has been mostly dormant up until now can disproportionately and adversely impact otherwise healthy children and young adults.
For those who haven't gotten the vaccine yet, county officials here say it's not too late since the peak of the flu season is still weeks away.
Krueger said, "The middle age group tends to be untouched so they figure they don't need to, why make time for it, but when we see these brand new viruses come around or continue to circulate, like they always do they're the ones at risk and it's really going to hit them hard."