A waterborne-disease outbreak at a campground near Zumbrota has sickened 72 people, making it one of the largest in the state in recent years, the Minnesota Department of Health said Friday.

The Shades of Sherwood Campground has taken steps recommended by the agency, including hyperchlorinating its swimming pool, closing a nearby man-made pond and posting signs that warn anyone with diarrhea to refrain from swimming.

“We believe that the steps that have been taken at this time would limit ongoing risk,” said Trisha Robinson, supervisor of the waterborne diseases unit at the Department of Health.

At the same time, campground owner Mike Thoreson challenged the state’s account of the outbreak, saying most of the cases have not been confirmed by laboratory tests and that the agency hasn’t tested his pool or pond.

Thoreson said the health of his customers is paramount, but said the state has used a heavy hand in its public notices that is hurting his business.

“Obviously we don’t want anybody to be sick, that is why we worked with the Health Department on every single recommendation,” he said. “What is misleading about this is they have no more confirmed cases than when they started with this a month ago,” said Thoreson.

Last week, the Health Department sought input from anyone who had visited the campground since July 1 to help it investigate the outbreak. It involves a diarrheal disease caused by a microscopic parasite called Cryptosporidium, which is spread by humans ingesting water that contains fecal matter.

The department said it was asking the public for help because its “investigators have been unable to get key information from the facility itself.”

The department received so many calls its voice mail box filled up, prompting it to take to Twitter to ask people to keep trying or send e-mails.

Thoreson said state officials asked him to turn over his customer lists, but he refused because he didn’t know if it was legal for him to do so. Instead, he said, the next day the agency issued a news release.

“Honestly, I think it was out of spite,” he said.

So far, the state’s disease detectives have confirmed four infections through testing. Two people have been infected with the Cryptosporidium parasite, one with an E. coli infection that produces a toxin called Shiga, and one person has been infected with both.

The 68 other cases involve people who reported getting sick after staying at Shades of Sherwood and having symptoms consistent with those infections. On average, people were sick for six days. Lab tests are pending for some people, but Cryptosporidium usually leaves the body after two weeks.

The water sources at the campground were not tested, Robinson said, because such tests are so unreliable that they are not standard in waterborne disease outbreaks.

Robinson said interviews with those affected have ruled out any other source of infection. “The evidence here is overwhelming that it was Shades of Sherwood,” she said.

‘Very hardy’ parasite

The campground typically gets about 2,000 visitors a week, but Thoreson said the “panic” caused by the Health Department is causing cancellations and a loss of tens of thousands of dollars in revenue.

“Cryptosporidium is the number one waterborne recreational illness in the country,” he said. “You can get it from anywhere.”

Robinson said the campground has cooperated in the past week, including voluntarily closing the pond, which unlike the swimming pool, cannot be treated to eliminate the “very hardy” parasite.

“We do have a lot of evidence that finds their only exposure in the campground was going in this man-made pond,” she said.

Thoreson said he will protect the reputation of his business.

“For any business owner ... out there, they shouldn’t think that this isn’t something they shouldn’t be immune to,” he said.