Just as an outbreak of one type of gastrointestinal illness in Dane County seems to be declining, another is on the rise — among University of Wisconsin students.

More than 100 students have been reported ill the past week with vomiting and diarrhea in an outbreak thought to be caused by norovirus, Dr. Sarah Van Orman, executive director of University Health Services, said Friday.

At least 63 of the cases are students living in Sellery Hall, where crews have been cleaning the bathrooms at least seven times a day to stop the spread of the illness, Van Orman said.

Most of the other cases have been in fraternity and sorority houses, with a few among students in off-campus housing.

Lab tests are pending to verify norovirus, which causes a sudden onset of vomiting and diarrhea and generally lasts 24 to 48 hours.

The virus, one cause of the "stomach flu," is easily spread among people by contaminated hands, surfaces or foods.

Regardless of whether the bug is norovirus or something else, Van Orman said, the advice remains the same: Students and others on campus, and people anywhere in the Madison area, should wash their hands frequently, especially after going to the bathroom and before preparing or eating food.

"We see lots of this every year," she said. "It's just that now we're seeing more of a clustering and an outbreak."

The county, especially Madison and the eastern part of the county, has in recent months experienced an outbreak of shigellosis, another cause of the "stomach flu."

At least 148 cases of the bacterial illness have been confirmed since July, most of them in September or October, said Amanda Kita-Yarbro, an epidemiologist with the Madison-Dane County Health Department.

That's roughly ten times more of the illness than was seen the past two years during that period. Frequent handwashing also is the best way to prevent shigellosis.

Just three cases of the illness were reported this week and four last week, down from more than dozen a week in previous weeks, Kita-Yarbro said.

"I don't think I can say the outbreak is over, but it seems to be decreasing," she said.