Fairgoers take note: Federal health officials have identified a new strain of swine flu and issued guidelines Friday urging people to take precautions if they plan to come in contact with pigs this summer.

Twenty-nine cases in eight states have been confirmed so far -- many of them in children -- including 12 new cases announced Friday.

No human infections have been reported in Minnesota, but state officials are putting out an alert to local health departments and agencies that handle animals, said Kris Ehresmann, director of infectious diseases at the Minnesota Department of Health. The Minnesota Pork Producers Association is alerting farmers and the State Fair Foundation is reminding Minnesotans to wash their hands and to avoid eating in barns.

With fair season getting into full swing, "we're seeing a spike [in cases] right now," said Dr. Joseph Bresee, an epidemiologist at the U.S. Centers for Disease Control and Prevention, during a news conference.

Human symptoms are mild -- including fever, coughing, runny nose and sore throat -- but three patients, who also had other underlying diseases, required hospital care. Without testing, it is almost impossible to differentiate between swine and seasonal flu, said Bresee.

The new strain, termed H3N2v, is passed through contact with pigs, but not through eating or handling pork. "This is not a food-borne disease," said Bresee.

Fifteen of 16 cases reported in the past three weeks were probably related to contact with pigs at agricultural fairs. Ten were associated with an Ohio fair where reportedly sick pigs had been present. Bresee said he expects more cases to pop up in the next few weeks.

In counties across Minnesota, more than 40 fairs are planned for August, including the State Fair, which ends Labor Day weekend.

'Promiscuous' gene matching

H3N2v, first detected in 2011, is not a major public health threat now because it does not easily jump from person to person. Plus, many people already have some immunity to it because a similar virus made its rounds in the 1990s, said Mike Osterholm, director of the Minnesota Center of Excellence for Influenza Research.

Nonetheless, public health officials worry about H3N2v because the new virus acquired a gene from the 2009 H1N1 swine flu virus. While the gene may not make H3N2v more contagious, it has changed it enough that the immune system may not recognize it, Osterholm said. The gene might help the virus pass from pigs to people, and ultimately from person to person, more easily.

Current flu vaccines also don't protect against this virus. The CDC is working on a vaccine and is planning clinical trials.

Even if the virus were to become easily transmissible between people, Osterholm said, that wouldn't necessarily mean it would cause severe illness.

But, he added, keeping a close eye on flu viruses is important because they change rapidly. Influenza viruses, which mix and match genes constantly, "are some of the most promiscuous viruses in the world," he said.

Daniela Hernandez • 612-673-4088