Maryn McKenna writes in Mother Jones that the ways that farm kids and their families handle pigs at agricultural fairs put them at risk for novel flu viruses that are circulating among swine, and the close contact between children and show pigs could be a bridge that allows new flu strains to spread widely among humans.

That’s the warning in an analysis just released by the scientific journal Emerging Infectious Diseases, which is published by the Centers for Disease Control and Prevention. The risk can be reduced, the analysis says, but exhibitors and visitors need to take steps to protect themselves.

“We’re bringing animals and people from multiple, diverse backgrounds into close proximity to each other for a prolonged period of time—these shows can go on for a week or more,” said Dr. Andrew Bowman, an assistant professor at Ohio State University and the senior author on the study. “The analogy I use is kids in preschool: If one brings in something, by the end of a week they’ll all have it.”

In the summer of 2016, 18 kids and adults who were part of families that showed pigs came down with novel strains of flu after attending seven fairs in Ohio and Michigan. That was the latest outbreak in a slow wave that has been washing through state fairs since the summer of 2012, when 306 people caught swine flu from pigs at fairs; 16 were sick enough to be hospitalized and one person died.

“Swine flu” might be familiar; it was what people called the pandemic of 2009, when a new variant of flu that moved from pigs to people swept the world and made millions sick — only mildly so, fortunately, instead of the dire illness that killed millions of people in the “Spanish flu” pandemic of 1918.