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Campground closes pond after parasite investigation

August 12, 2018 GMT

The Minnesota Department of Health and Shades of Sherwood campground in Zumbrota are working together to reduce risks after a waterborne parasite sickened people who had visited the campground

After announcing an investigation into cryptosporidiosis, a diarrheal disease caused by the parasite cryptosporidium, the health department has heard from 72 people who exhibited symptoms of the illness.

In an effort to prevent additional illness, the MDH recommended several steps, which Shades of Sherwood followed.


The swimming pool at the campground was temporarily closed and hyper-chlorinated to kill any existing cryptosporidium. It has since reopened.

Shades of Sherwood posted signs warning visitors to not swim for two weeks if they have been ill with diarrhea. MDH recommends the measure to reduce the risk of shedding the parasite in water and passing it to other swimmers.

The campground’s man-made water pond is closed to swimmers. There is not a good way to treat or clean natural water sources that might contain waterborne pathogens, according to Trisha Robinson, an epidemiologist and waterborne diseases unit supervisor with the MDH.

“Unfortunately, in a man-made pond like that, there isn’t a timeline we can give,” Robinson said.

She said freezing winter weather should help kill off the parasite. The MDH recommends that Shades of Sherwood keep the pond closed for the rest of the season.

Several of the people who reported symptoms told the MDH they had only swum in the pond, Robinson said. But others reported they had only been in the Zumbro River.

It’s possible that some people picked up a parasite or bacteria from one water source and then returned to re-contaminate another over the last month or so, Robinson said.

“In a place where people are exposed to multiple venues, the pool, the river, and the pond, we will probably never know whether there was a single, original source,” Robinson said.

Mike Thoreson, the owner of Shades of Sherwood, argues that 72 illnesses – few of which are lab-confirmed – of the “thousands of people who have been in here” should not be considered an outbreak.

Thoreson has followed all of the MDH recommendations. The safety of the general public is currently Shades of Sherwood’s biggest concern, he said.


The MDH has confirmed three cases of cryptosporidiosis in the lab, Robinson said, one of whom had shiga toxin e. coli. One more person who presented with symptoms was found to have e. coli as well.

The MDH is limited by the difficulty of investigating recreational waterborne diseases, Robinson said earlier in the week.

“Water testing in general has a lot of limits to it,” Robinson said. “If we take a sample from one area and it’s clear, sometimes three feet over it may not be.”

Cryptosporidium caused about half of the waterborne illness outbreaks in Minnesota between 2008 and 2017. Between 350 and 450 cases are reported in the state each year.

The parasite spreads through contact with fecal matter from infected people or animals. It is the most common cause of waterborne illness in the U.S., as it survives outside the body for long periods of time and is resistant to chlorine.

The symptoms of cryptosporidiosis include watery diarrhea, stomach cramps, vomiting, weight loss, and a low fever. Symptoms generally appear about a week after exposure, but can arrive in as little as two or as many as 14 days.