OWATONNA, Minn. — An Owatonna High School senior has died after experiencing flu-like symptoms.

Shannon Zwanziger, 17, was sick for a week. Her father, Terry Zwanziger, told the Owatonna People's Press (http://bit.ly/1yCxbgn ) that her symptoms worsened then her heart stopped Tuesday morning. She was flown to the Mayo Clinic in Rochester where she was pronounced dead.

Tests results are pending to determine whether Shannon had influenza. Terry Zwanziger said that the family was told that a "full gamut of tests" had to be run and that results may not be available for eight to 12 weeks. He also said she had not had a flu shot this year.

Shannon was one of more than 100 OHS students absent between last Thursday and Monday because of flu-like symptoms on Friday, 179 students were reported ill.

Principal Mark Randall said those numbers are at least double from last year at this time, but they were declining by Wednesday. In a letter to parents, he said the school is taking necessary precautions to insure the health and safety of its students.

Minnesota Department of Health spokesman Doug Schultz said southern Minnesota is seeing a high level of influenza activity.

Last week, the federal Centers for Disease Control and Prevention said the predominant influenza viruses this season have "drifted" from the strain for which the vaccine was developed, which could mean the vaccine is less effective.

"It's reasonable to assume the drifted strain has arrived in Minnesota," Schultz said. "With it, we tend to see more illness and more severe cases."

Schultz said everyone should get flu vaccinations this year. Although it may not provide complete protection, it's the best tool available.