MARSHALL - The City of Marshall and the Marshall Area YMCA closed their swimming pools Thursday after two confirmed cases of the waterborne disease-causing organism Cryptosporidium were reported on Wednesday.
The victims, both under 18, reported using the Marshall Aquatic Center pool within two weeks prior to becoming ill, according to Trisha Robinson, an epidemiologist with the state Department of Health.
"The disease is caused by a protozoan parasite and is typically introduced into a body of water by an ill swimmer," Robinson said. "The difficult thing about detecting it is, the time from exposure to illness can be as short as two days or as long as two weeks."
The organism is hardy and resistant to concentrations of chlorine ordinarily found in pools and drinking water, and spores can survive lengthy amounts of time outside a host, Robinson said.
According to Preston Stensrud, certified licensed pool operator, city personnel started raising the level of chlorine in the city pool at 4:30 pm on Wednesday.
"Basically per health code you have to raise the chlorine levels to 20 parts per million," Stensrud said. "Up to 5 ppm is considered normal. Now we're letting it decline to safe levels. We're assuming chlorine will have dropped to safe levels by Friday."
Health codes call for elevating chlorine levels in the water for 15 hours, Stensrud said. Afterwards, natural processes should lower the level of chlorine by evaporation.
YMCA Executive Director Tom Bolin said he was contacted by the state Department of Health and was advised to start disinfection as a precaution, assuming that people who use the Marshall Aquatic Center might also swim at the YMCA.
"The Department of Health came here, and as presumptive preventative measures we have closed the pool and are shocking the water with 20 ppm for the required time," Bolin said. "Our principle concern is the safety of our members and staff and we'll follow the directives of the Minnesota Department of Health until we're told we can open the pool again."
Marshall Community Services said the city pool will reopen today with 8 a.m. swimming lessons.
Bolin said reopening the YMCA pool is likely to take several days longer, since the YMCA has an indoor pool.
According to a Minnesota Department of Health fact sheet, Cryptosporidium is a parasite that is one of the most common waterborne diseases in the country, and is frequently found in drinking and recreational water. Symptoms of the disease cryptosporidiosis include diarrhea, stomach cramps, loss of appetite, weight loss, and a slight fever.
"Symptoms stick around longer than most protozoan illnesses," Robinson said, "and even after symptoms go away victims can still be infectious. If they've had the disease they should not go swimming anywhere, not a pool or a lake while they have diarrhea or for two weeks after."
Though the disease is not generally fatal, it can be serious to people with compromised immune systems, Robinson said. About 20 percent of cases in Minnesota require hospitalization.