Summer. Translated into the language of liquid fun, it means water parks, river rafting, neighborhood pools and beaches. It also means uninvited guests that are doing the backstroke with you, like parasites with hard, chlorine-resistant bodies that people don't even know they are harboring or spreading.

The result is a poolside view from the restroom.

What lurks beneath

In contaminated water, not only might you find E. coli, and other moderately scary viruses and bacteria that will literally make your skin crawl, but also a parasite, Cryptosporidium, nicknamed, crypto. "It's very small about the size of a red blood cell, and very difficult to filter out of the water," says Cynthia L. Chappell, Ph.D. and professor in the Division of Environmental and Occupational Health at The University of Texas School of Public Health at Houston.

Cryptosporidium infects many animal species, including cows and horses, that then spread it to humans, says infectious disease specialist Pablo C. Okhuysen, M.D., professor in internal medicine at The UT Medical School at Houston. He points out that, "It takes only a few parasites to infect someone, but an infected animal can pass several million a day."

But animals are not the only way crypto can be spread, explains Chappell.  One form passes directly from human to human, often from infected children who sometimes get exposed at day care centers or from playing with other children.  “This can be a particular problem with children who have become mobile but are not potty trained and don’t yet practice good sanitary habits,” she says.

Hard to crack

Another feature of Cryptosporidium is that it exists in water as an oocyst form: in other words, one really hard-shelled yoke. It has a Teflon-tough outer covering that protects it in an adverse environment—so well that adding chlorine to the water isn't very effective. "Chlorine will only kill a portion of the parasites, and only if they are in contact over a long period of time," Chappell says.

Cryptosporidium can live in fresh water for months. Chappell says that in pools and water parks, even a "shock" procedure (chlorine raised to extreme levels that would kill most bacteria and viruses) still might not penetrate this parasite's shell.

Most crypto infections cause diarrhea that can range from mild to severe.  In a healthy person, the diarrhea caused by crypto may last only a few days. Danger of dehydration is the biggest problem people might have.

Specific populations are at risk for complications: the very young and old, those with compromised immune systems from illness or certain medications, or dialysis patients. "Most people resolve it on their own," Okhuysen says, but adds, "If you have prolonged diarrhea, Cryptosporidium might be one of things that could be causing it."

Water park blues

Chappell says that public recreational facilities boost the number of outbreaks. "If you look at the reported cryptosporidiosis cases in any one year, and we repeat this year after year, you'll see a big spike in the summer.

"Researchers in the field and the CDC (Center for Disease Control and Prevention) are convinced that these recreational parks are a major source of infection. Not just the big water parks, but people are traveling, staying in hotels and motels. Sometimes those pools are not as well tended as people think they are."

It lives!

Several animals are hosts to this parasite that lives in the small bowel, so it is spread easily. Parasites depart through fecal material and are shed into water where they live until they find another host.

After rains and floods, cryptosporidia can enter water systems and infect large populations if not detected. In the 1994 outbreak in Milwaukee, the Wisconsin Division of Health estimated that 403,000 people were infected after the water system was polluted with cryptosporidia.

"While it doesn't multiply in water, only in a host, some water treatment plants cannot take care of it effectively, and sometimes cryptosporidia can also contaminate water wells," Okhuysen says.

Chappell adds that with large amounts of rain and flooding, the water treatment plants have a difficult time because there is so much to filter out, such as mud and particulates. "Everything gets stirred up with rain runoff. It's always more difficult to provide safe water at that time."

EPA regulations have been strengthened, but she says, "They can never say that they have removed this organism 100 percent."  Ultra violet light exposure or irradiation of the water is used sometimes as the last step in the treatment process, but those methods have proven to be too expensive for many water treatment systems.

Crypto isn't the only culprit in the pool, stream, ocean or water park. You can get diarrhea from E.coli and Shigella, among others. But Cryptosporidium is one of toughest to remove. Since chlorine is not effective, removing the water and starting over may be the safer solution for family pools. Heating water to a boil will kill the parasite, but that is rarely practical.

Wash before swimming

If someone had diarrhea earlier in the day, or even a few days before, the residue on the skin can still contaminate the water. The more people in the water, such as with water parks and public pools, the greater chance of contamination.

"Even after the diarrhea goes away and you feel quite good, you continue to pass these cysts for up to a week or two. People think they are over it, but they haven't completely cleared the parasite from their systems, and they are still infectious to others," Chappell explains.

The parasite is relatively common in daycare facilities and other institutional settings such as nursing homes or, "anyplace you have people who may not be able to participate in good bowel habits."

Chappell adds, "If you go into the generally healthy populations, you are still going to find one-third to one-quarter of the population have antibodies to this organism in their blood stream. So they've had it at some time."

Parents should follow these suggestions:

• Wash children—and their own hands—well before going swimming
• Take children on frequent bathroom breaks during their swim time.
• Change diapers in a bathroom, rather than near the water.
• Instruct children not to swallow water, if possible.

For other tips, visit www.cdc.gov/healthyswimming/.

Last Updated: 7-15-2008

Editorial Board | Legal Disclaimer | Privacy & Security | Contact Us

©2000-2009 Office of Institutional Advancement, UT-Houston