Three cases of swine flu have been reported among visitors at the Minnesota State Fair, only the sickened visitors didn't contract the new flu strain that has triggered national concern in recent weeks.

One of the victims was a teenage girl who was exhibiting pigs. She became ill on Aug. 26, the fourth day of the fair, and sought treatment from a State Fair nurse. The others were a school-age boy who spent "all day in the swine barn on Aug. 24" and became sick three days later, the state Health Department said Friday, and a woman in her late 70s who also had spent considerable time around the swine barn and swine show that day.

The elderly woman was hospitalized briefly. All three are now recovering.

Their illnesses were detected in part because of the fair's heightened concerns about an H3N2v strain of swine flu that has circulated nationally at livestock fairs and animal markets.

That virus has been found to spread easily from pigs to humans, and was linked to illnesses of two young siblings at a Dakota County animal market earlier this month. But the three sickened people at the State Fair were infected by a different H1N2v strain. Lab tests from the U.S. Centers for Disease Control and Prevention have confirmed one of the infections. Test results regarding the other two are pending.

So far the new strain of influenza resembles ordinary seasonal flu, with symptoms including fever and runny nose. But health officials have been on high alert because flu viruses can mutate and spread rapidly after jumping from one species to another.

"For the past two weeks, we have been looking very hard for cases of influenza in people who have been exposed to swine," said Richard Danila, deputy state epidemiologist. "We have also worked closely with our veterinary colleagues to remain informed about potential infections in swine at the fair."

So far this year, H3N2v has sickened nearly 300 people in the U.S., mostly children or exhibitors at agricultural fairs in the Midwest. The first death related to the infection was reported on Friday, and involved a 61-year-old woman with other health problems who had visited a county fair in Ohio.

Concern about the virus prompted Health Department and State Fair officials to take extra precautions, including encouraging people at high risk of flu complications to consider skipping the swine barn and the popular Miracle of Birth Center exhibit this year. Fairgoers were also encouraged to keep food out of the swine barn and to wash their hands upon exiting the building.

With three days left for the fair, state officials said they aren't changing those recommendations.

Routine surveillance of pigs in the swine barn earlier in the fair had identified two animals infected with the H1N2v strain. They were removed from the public barn. Veterinarians will continue to evaluate any pigs brought to the fair for competition.

Jeremy Olson • 612-673-7744