MADISON, Wis. -- Many have questions about the H1N1 flu, and some are wondering about the difference between H1N1 and seasonal flu.

H1N1 is keeping staff at area emergency rooms very busy.

At St. Mary's Hospital, one out of every five who come into the emergency room are coming in with influenza-like illnesses and most are H1N1 cases.

"It's more prevalent than what you would expect at this time of year," said Dr. Aaron Ray, who works in the emergency room at St. Mary's Hospital.

And from the H1N1 cases he has seen, Ray said the symptoms nearly mimic those of the seasonal flu.

"As far as the actual overall severity of the symptoms, I don't think I've noticed any profound change between the two," Ray said.

Stephanie Marquis, of the state Department of Health Services, said the two have very similar symptoms -- but the big difference is who the viruses target.

"H1N1 is definitely hitting younger children much harder than seasonal flu," Marquis said. "Seasonal (flu) tends to hit older adults harder."

Doctors said both flu strains can make people feel ill and sideline them for a few days -- but H1N1 is hitting different age groups hard. Last year, no children died from seasonal flu. This year, so far, five children have died from H1N1. Most, if not all, of those cases have involved those with an underlying health condition.

"What we're really concerned about is that mortality rate of the children," Marquis said. "They essentially have two flu seasons that they have to go through."

Typically, Wisconsin sees about 600 to 900 seasonal flu-related deaths a year, but that's just an estimate because flu is not a reportable illness.

So far this year, there have been 15 deaths related to H1N1, but public health officials said the data can't really be compared yet because it's very early and they won't have a good grasp on the numbers until the H1N1 season ends.