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The ABCs of Cryptosporidium

Imagine this: It’s peak season at your water park. Business is great, the weather is perfect, and patrons are enjoying a fun summer afternoon.

Then, your staff receives a call from your local health department, claiming five people are complaining of stomach cramps and diarrhea after visiting your facility a few days ago, and one has already tested positive for cryptosporidiosis.

Now instead of running the daily operations of your facility, your staff is shooing customers out of your pools and preparing to close for what could be multiple days. And instead of a great place for a family to enjoy a summer’s day, your water park is a biological hazard and the epicenter of a potential cryptosporidiosis outbreak.

Scenarios like this are becoming increasingly common in recreational water facilities around the world. From May 11 to June 7 of this year in the North East, Yorkshire, West Midlands, and East Midlands regions of the United Kingdom, reported cases of cryptosporidiosis rose to nearly four times what they were last year, from 82 cases to 327. Meanwhile, the most recent Centers for Disease Control (CDC) statistics show cases of cryptosporidiosis in the United States have increased 200 percent from 2004 to 2008.

A 2008 CDC survey studied 134 recreational water illness (RWI) outbreaks reported in 38 states and Puerto Rico over the course of the year. Cryptosporidium was responsible for 60 of the 134 outbreaks, amounting to 44.8 percent and making it the most common RWI in the United States.

 “Cryptosporidium is a highly successful parasite because it is resistant to chlorine, multiplies quickly within a host, and is easily transmissible,” says Dr. Mike Belosevic, professor of public health at the University of Alberta.

According to Belosevic, very low numbers of parasites can cause an infection because Cryptosporidium multiplies rapidly within its host. If as few as 10 oocysts, thick-walled spores that transmit the pathogen, invade a new host, the host could be infected with millions of oocysts in a matter of weeks.

Effects of Cryptosporidiosis
Humans contract cryptosporidiosis by ingesting water infected with the parasite Cryptosporidium. Water becomes infected when feces from someone carrying Cryptosporidium are deposited in a body of water. 

Once cryptosporidiosis is contracted, those afflicted host the parasite in their small intestine. After the immune system recognizes the parasite, the body attempts to flush it out, causing diarrhea. For most people, diarrhea and stomach cramps are the extent of the symptoms experienced. These typically last up to two weeks, but a host can carry and spread the parasite with each bowel movement for four to six weeks, well after symptoms have stopped.

However, for those with weakened immune systems, such as those undergoing chemotherapy or with HIV, cryptosporidiosis becomes far more dangerous, potentially even fatal.

“If someone’s immune system is in really bad shape, they may never quite clear the disease,” says Michele Hlavsa, an epidemiologist for the CDC’s Waterborne Disease Prevention Branch. “It’s possible that they have so much diarrhea that they stop absorbing nutrients, which is where they get in trouble.”

Though no drug is available to combat cryptosporidiosis, Liz Hedstrom, Ph. D., a professor of biology at Brandeis University, has been working to develop one for nearly 10 years.

“We have identified a compound that has shown activity in mice,” Hedstrom says. “But we are still a long way off from making a drug available to the public.”

Hedstrom estimates it could be at least 10 years before anything is even submitted for approval from the U.S. Food and Drug Administration. Until then, people with cryptosporidiosis have no choice but to let the disease run its course and hope their immune systems are up to the challenge.

Preventing an Outbreak
One of the main factors behind Cryptosporidium in recreational pools and water parks is the ability of the parasite to survive in properly chlorinated water for up to 10 days. Over the past few years, new methods of water sanitization have made containing Cryptosporidium much more feasible.

UV and ozone treatments have both been proven to contain Cryptosporidium and have been strongly recommended as secondary means of water sanitation by the soon-to-be-published Model Aquatic Health Code (MAHC). The MAHC will serve as an adoptable model for any governing body looking to regulate aquatic facilities.

A few water parks have already made the transition to ozone or UV treatment. KeyLime Cove in Gurnee, Illinois, a 420,000-gallon indoor water park, has had an ozone sanitation system since it opened in 2008.

 “It gives us a higher customer experience factor,” says General Manager Dale McFarland. “It is more expensive [than chlorine], but from a guest standpoint, you may be compensating them in another way down the road.”

Franceen Gonzales, vice president of risk management at Great Wolf Lodge and member of the IAAPA Safety Committee, oversees several indoor water parks containing UV sanitation systems and agrees: “Any time it is possible to prevent the spread of a disease that is very difficult to detect and control under normal operating conditions, then it is worth the expense.” 

The CDC recommends these methods be used in combination with chlorine to provide residual disinfection and to cover for any inconsistencies in water circulation through ozone or UV systems. Also, the CDC urges recreational water facilities to strictly enforce a shower-before-swim policy with all guests and to watch out specifically for children wearing diapers or being toilet-trained. Since contact with fecal matter is the predominant way that Cryptosporidium spreads, proper bathing before entering recreational water is strongly recommended.

A diarrheal incident in the water is the most common and highest-risk event that can infect your water with Cryptosporidium. One diarrheal incident can release anywhere from 10,000 to 100,000 Cryptosporidium oocysts. Ten of these oocysts have the potential to infect a human being.

Responding to an Outbreak
Often facilities will not know they have Cryptosporidium in the water until a few cases of cryptosporidiosis have surfaced. Once there is a possible report, it is considered best practice to close the facility and immediately superchlorinate.

Though they have never experienced an outbreak, Gonzales and Great Wolf Lodge have a protocol in place to respond to a claim of cryptosporidiosis stemming from one of the company’s facilities.

“If we receive a claim, we contact the local health department and work with them to determine the validity of the claim,” Gonzales says. “We collect and test our water, and in abundance of caution, super-chlorinate overnight after we receive the claim. We monitor for additional complaints of illness as well.”

Recreational water must have a concentration time inactivation value of 15,300 to effectively kill Cryptosporidium. This can be achieved by maintaining a free chlorine concentration of 20 parts per million for 765 minutes (nearly 13 hours) or maintaining a free chlorine concentration of 10 parts per million for 1,530 minutes (25.5 hours). In either scenario, the water must have a pH level below 7.5 and a temperature above 77 degrees.

Once the water has been hyperchlorinated for the recommended amount of time, the CDC considers it safe to allow swimmers in the water once the chlorination is returned to a normal level.

Future Outlook
Although Cryptosporidium remains the number-one cause of RWIs across the globe, new methods of water sanitation have made the chance of a large outbreak less likely. Ozone and UV sanitation systems, in combination with the practice of proper preswim bathing, reduces the likelihood of cryptosporidiosis outbreak a great deal.

The adoption of the MAHC will make ozone and UV sanitation systems the norm among recreational water facilities and should reduce the dramatic increase in outbreaks the world has experienced in the past few years.

Contact Scott Cahoon at

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