MINNEAPOLIS — Dr. Jeff Bender admits that he and his colleagues were a strange sight, wandering through the swine barn at the Minnesota State Fair, taking nasal swabs from pigs.

But it was all in the name of science.

Now Bender, a University of Minnesota veterinarian, has released the results of his study, and it contains a word of caution for anyone planning to visit the State Fair:

Even healthy-looking pigs might have the flu.

The study, being released Wednesday, comes on the heels of recent reports that more than 150 people in other parts of the country have contracted a new type of swine flu, apparently after contact with pigs at state or county fairs.

“This study just shows that viruses are shared between pigs and people,” Bender said — and that it may be harder to spot an infected pig than once thought.

“We were expecting, boy, if pigs had virus then they should be (feverish), sick” and easy to screen out, he said. Not anymore.

So far, no cases of the new swine flu, known as H3N2v, have been found in Minnesota, according to health officials.

It has mostly affected children in two states: Indiana and Ohio, and is similar to seasonal flu, with symptoms including fever, cough, runny nose and body aches.

In Minnesota, State Fair officials say they’ve stepped up precautions in advance of the hundreds of thousands of visitors who will begin descending on the fairgrounds on opening day, Aug. 23.

Veterinarians plan to check the livestock when they arrive and will monitor the pigs more frequently than in the past, said Brienna Schuette, a State Fair spokeswoman.

Visitors will also see signs posted at all livestock barns, urging simple steps to prevent the spread of illness: Avoid eating in the barns; use hand-washing stations after visiting, and skip the barn if you feel ill.

The Minnesota Department of Health, in fact, suggests that people at high risk for flu should consider avoiding the swine exhibit entirely. That includes children younger than 5, pregnant women, people 65 and older and those with chronic conditions.

In his study, Bender tested pigs at the Minnesota State Fair in 2009, during the height of the H1N1 flu pandemic sweeping the country.

At the time, the flu was so widespread that there was even an outbreak among 4-H members during the State Fair.

Bender and his team donned gloves to collect nasal samples from 102 apparently healthy pigs at the Minnesota and South Dakota state fairs. They also asked the animals’ owners to fill out lengthy questionnaires.

The scientists found that 11 of the 57 pigs swabbed at the Minnesota State Fair — 19 percent — had the H1N1 flu virus. By comparison, the year before, none of the 47 pigs tested had the flu.

They also discovered that two exhibitors — a girl and her father — fell ill with the flu during the fair. Three of their pigs tested positive as well.

In this case, though, Bender believes that the people, not the pigs, were to blame.

“What we do know is that there was a lot of circulating virus in people,” he said. “Our suspicion is there probably was an exhibitor who brought it in and shared it with the pigs.”

His study is being published in the August issue of the journal Emerging Infectious Diseases.