At least three visitors to a Zumbrota, Minn., campground have contracted a potentially severe intestinal illness called cryptosporidiosis, and state health officials are investigating.

People who have visited the Shades of Sherwood Campground since July 1 are encouraged to contact the Minnesota Department of Health. Even people who didn’t get sick could provide clues to the outbreak’s origin, said department spokesman Doug Schultz.

“That’s the problem,” he said. “We need more information.”

Cryptosporidiosis is caused by a parasite spread through contact with fecal matter. Roughly 350 to 400 waterborne infections are diagnosed in Minnesota each year because of the parasite, which is resistant to chlorine.

Typical symptoms include diarrhea, cramps, vomiting, loss of appetite, weight loss and low-grade fever. Swimmers can still spread the parasite two weeks after symptoms cease.

The Zumbrota campground has a standard swimming pool and a broader recreational pool with a river for tubing.

State officials say they haven’t been able to get the kind of cooperation from the campground that they typically get from facilities involved in outbreaks.

Those who became ill were all adults. One was hospitalized.

Jeremy Olson