The next time you dive into a sparkling public swimming pool, you might want to look and see how many other swimmers are enjoying the water with you. A large number of bathers, especially if they include toddlers and children in diapers, increases the likelihood that you will become infected with a recreational water illness.
Many people assume that a well-maintained swimming pool is germ-free, that chlorinated water is just as clean as drinking water, and that chlorine kills all germs instantly. But this is not true. Even the best-maintained pools with adequate chlorine levels (1 ppm to 3 ppm free available chlorine) can transmit waterborne diseases.1
Cryptosporidium and Giardia are fecally transmitted protozoan parasites that have been linked to outbreaks of GI illnesses from swimming pools and water parks. These common intestinal parasites can withstand chlorine disinfection for a considerable period of time. For example, Cryptosporidium excreted in the feces of infected humans can survive and remain infective for nearly 11 days, and Giardia can survive at least 30 to 60 minutes.2
With Cryptosporidium, a single fecal accident can contaminate an entire pool, and swallowing a few mouthfuls of water can result in an infection. With Giardia, swallowing as few as 10 cysts of Giardia (the infectious form) can cause an infection. Fecal accidents are not uncommon in pools. Each day, up to 2 to 3 pounds of feces can be found in the water of an average-sized public pool from fecal accidents and from swimmers’ bodies from improper cleansing after bowel movements.1
Nurses need to be informed about the parasites found swimming in public pools, signs and symptoms associated with them, treatments available, and preventive measures. With this information, nurses can better recognize waterborne illnesses and educate patients and community members about preventing and avoiding such illnesses.
Children who play in water parks with interactive water features — such as fountains, shallow pools, vertical pressure jets, and overhead sprays — may be at greater risk for Cryptosporidium and Giardia infection and other recreational water illnesses than children who use swimming pools. A spray park is an ideal setting for an outbreak. Parents often bring children in diapers to spray parks because they require no swimming skills, putting the children at high risk for contamination resulting from fecal accidents and the rinsing of contaminated bodies in the water.3 Water from the interactive features is usually collected in an underground holding tank and recirculated back up through the waterspouts. If the underground tanks are not well designed with high-level filtration and water-sanitizing systems, water is at high risk of microbiological contamination and poses a high risk of infection to children.3
Conventional chlorination and filtration in well-maintained pools and water parks are effective against chlorine-sensitive pathogens, such as E. coli O157:H7, Shigella, and norovirus. With Giardia, chlorine is effective in 30 to 60 minutes, and cysts are large enough (10 to 20 microns) to be caught in conventional pool filters. But the small size of chlorine-resistant Cryptosporidium oocysts (the environmentally resistant form of Cryptosporidium) allows them to escape conventional pool filtration, so neither chlorination nor filtration can prevent their transmission from infected swimmers, who can pass oocysts in their stool for weeks after symptoms resolve.
Cryptosporidium, a single-celled protozoan parasite, is the leading cause of gastroenteritis outbreaks associated with treated recreational water in the United States. Infection begins when people ingest Cryptosporidium oocysts from drinking water or recreational water contaminated with excreta. Ingesting as few as 10 to 30 oocysts can lead to severe disease and persistent infection.6 After ingestion, the oocysts are activated in the stomach and upper intestines. This causes each oocyst to release (excyst) four motile sporozoites (the stage in the life cycle after oocyst — before infection of new host cell) that attach and invade the epithelial cells lining the GI tract.6 Cryptosporidum have a special preference for the jejunum and terminal ileum. Within these cells, the sporozoites mature asexually into meronts (the stage during which asexual division occurs) that mature and release four to eight motile merozoites into the intestinal lumen. The merozoites can reinvade other host cells or undergo sexual maturation to form new oocysts that can begin a new life cycle in the host or can be excreted into the environment. Each generation can mature in as little as 12 to 14 hours. Oocysts are immediately infectious when passed through the feces and can survive in the environment for more than six months if kept moist. They are difficult to eradicate from water because of their small size of 4 to 6 microns (for perspective, a grain of table salt is about 90 microns) and their resistance to chlorination. In fact, Cryptosporidium oocysts can be incubated for up to two hours in household bleach without reducing their infectivity. Oocysts can be found in 65% to 97% of surface waters and are sporadically detected in tap water. Low-grade contamination has been documented in 24% of treated water.4,6,7
During the last three years, the number of Cryptosporidium cases reported to the CDC has risen substantially. In 2005, 2006, and 2007, the number of nonoutbreak cases increased 41%, 24%, and 66%, respectively. Increases in outbreaks at treated water venues, such as swimming pools and water parks, were also reported in 2006 and 2007.8
Symptoms of cryptosporidiosis appear in seven to 10 days (range: five to 28 days) after ingestion of the oocysts. In immunocompetent people, the most common clinical symptom is a profuse watery diarrhea that is generally self-limiting and lasts from several days up to a month. Abdominal cramps, low-grade fever, nausea, vomiting, dehydration, anorexia, and weight loss often accompany the diarrhea. At the height of infection, an infected person can pass as many as 100 million to 1 trillion oocysts with each bowel movement.9 After recovery, relapse is common. Symptoms reoccur in nearly 40% of patients following a diarrhea-free period of several days to several weeks. After full recovery, people shed oocysts in stools for months.6,7
Cryptosporidiosis is most severe in immunosuppressed patients. Symptoms can be debilitating with cholera-like diarrhea (up to 25 liters a day) and profound weight loss.6 The symptoms can become chronic, even lasting for years. In these patients, the parasites can spread throughout the gut and the billiary tract, and even to the respiratory tract.
Although contaminated water is the primary source for infection, the parasite can be transmitted in several other ways: 1) from animals through contact with the feces during lambing, calving, and manure spreading; 2) from younger children in daycare centers where diapering occurs; and 3) from contaminated raw foods.9
Diagnosis:Cryptosporidium infection is usually diagnosed by a microscopic examination of the stool. The lab receiving the stool sample should be alerted that it may contain Cryptosporidium oocysts since regular ova and parasite examinations will not detect them. Direct fluorescent antibody assays (DFA) are extremely sensitive (99%) and considered the gold standard for testing. Antigen detection kits (if the specimen is fresh) and polymerase chain reaction (PCR) are the other methods used to diagnose Cryptosporidium.9,10
Treatment: No reliable treatment exists for cryptosporidiosis.6,10 Most immunocompetent patients recover within a few weeks without treatment. Patients with voluminous, watery diarrhea may need oral rehydration supportive therapy with fluids that contain sodium, potassium, carbonate, and glucose. Loperamide (Imodium) and diphenoxylate/atropine (Lomotil) can reduce symptoms in mild to moderate disease. Tincture of opium (Paregoric) can be used for patients who do not respond to the milder agents. Nitazoxanide (Alinia) is the only broad-spectrum antiparasitic drug approved in the U.S. for treating Cryptosporidium infection. This medication results in a cure of diarrhea in about five days for 72% to 88% of patients. However, 25% to 40% of cured patients continue to pass oocysts in their stool. Using nitazoxanide in immunosuppressed patients has not been successful.4,10
A wake-up call
Outbreaks: The public did not pay much attention to cryptosporidiosis until 1993, when 403,000 Milwaukee residents developed a diarrheal illness after their drinking water became contaminated. This was the largest outbreak of waterborne disease in U.S. history. Since then, with new federal drinking-water regulatory efforts, Cryptosporidium outbreaks in municipal waters have decreased. But the last two decades have seen a rise in outbreaks of Cryptosporidium related to contaminated water in pools and water parks. Although these outbreaks have not involved as many people as municipal drinking water outbreaks, they have occurred much more often.1 Last year, the CDC received reports of 18 Cryptosporidium outbreaks from recreational water venues, and that number is likely to rise as reports for 2007 are finalized.11
The largest outbreak related to swimming pools and water parks occurred in 2007 in Utah with 1,902 lab-confirmed cases of cryptosporidiosis. But this number may be deceiving. The CDC estimates that only 8% of people with diarrheal illnesses seek medical care. If only 8% of the cases were reported during the Utah outbreak, about 23,000 cases of cryptosporidiosis may have occurred. Nearly one-third of the reported cases were in children under 5; very few cases occurred in people over 45. To control the outbreak, Utah officials banned all children under 5, including children in diapers, from swimming in public pools, including pools at country clubs, hotels, and apartment complexes. In addition, operators of public pools had to increase levels of chlorination and hyperchlorinate weekly.12
Giardia lambia (also known as G. duodenalis or G. intestinalis) is the most commonly diagnosed waterborne (drinking and recreational) intestinal protozoan parasite in the United States, with an estimated 2.5 million cases annually. The highest infection rates occur in children under age 5, especially children in daycare centers, where Giardia cyst passage can be as high as 35% to 50%.4,13 Water is the major source of Giardia infections. In the United States, the parasite can be found in 80% of untreated (raw) water supplies in lakes, streams, and ponds and in as many as 15% of filtered municipal water supplies (drinking water).14
The pathogen’s life cycle consists of two stages: an infectious cyst that is passed into the environment and an active form, or trophozoite, that exists freely in the human small intestine. Infection begins with the ingestion of as few as 10 to 25 Giardia cysts from contaminated water.13 Once swallowed and exposed to gastric acid and pancreatic enzymes, the cysts release the pear-shaped, binucleate, multiflagellated trophozoites. The trophozoites (the feeding stage of the life cycle) attach to the wall of the duodenum and jejunum with a large ventral sucking disk. They absorb nutrients (glucose) from the intestinal lumen via diffusion or pinocytosis (the cellular process of actively engulfing liquid). After feeding, the trophozoite begins replicating every nine to 12 hours through longitudinal binary fission. The resulting trophozoites then pass into the large bowel, where encystation occurs in the presence of an alkaline pH and secondary bile salts. Cysts are then passed into the environment, and the cycle is repeated.14
Infected people shed more than 100 million to 1 trillion cysts in their stool each day and can excrete cysts for months. Cysts are about the size of a red blood cell. They are relatively resistant to chlorine and can survive in cold surface water for several weeks to months.13
With symptoms — or not
Giardiasis can present as asymptomatic infection with cyst passage, acute self-limited diarrhea, or a syndrome of chronic diarrhea with malabsorption and weight loss. Among people who ingest Giardia cysts, 5% to 15% pass cysts without developing symptoms, 25% to 50% become symptomatic with acute diarrhea, and 35% to 70% have no evidence of infection.4 Symptoms of acute giardiasis usually last from seven to 10 days and include diarrhea; malaise; flatulence; foul-smelling, greasy stools that may float; abdominal cramps; bloating; nausea; anorexia; and weight loss. Weight loss of about 10 pounds occurs in more than 50% of infected people.4,13 Patients who develop diarrhea lasting more than 14 days (chronic diarrhea) have profound malaise with diffuse abdominal discomfort exacerbated by eating. Patients usually loose a significant amount of weight (10% to 20% of their body weight). Periods of diarrhea can alternate with periods of constipation or normal bowel habits for months. With chronic diarrhea, steatorrhea (over 7 grams of fat lost in feces a day) and malabsorption of vitamin B-12, vitamin A, protein, and D-xylose have been documented.4,13
Diagnosis and treatment: The preferred method for diagnosing Giardia is the detection of cysts or trophozoites in the stool. Finding the parasite is difficult, so three stools taken at intervals over three nonconsecutive days is recommended. Duodenal fluid can also be examined for trophozoites. Other methods include antigen assays (ELISA) or immunofluorescence to detect antibodies to the trophozoites or cysts. Because Giardia can persist and lead to malabsorption and weight loss, infected patients should receive treatment. A number of drugs are available for treating giardiasis. Metronidazole (Flagyl) is the drug of choice. Other effective drugs include tinidazole (Fasigyn) and nitazoxanide.
Swimming is healthy. It’s the second most popular form of exercise in the U.S., with about 400 million person-visits to swimming venues each year. Water parks are also tremendously popular: In 2004, attendance exceeded 73 million.15 But most people are not mindful that pools and water parks should be considered communal bathing sites. In any pool or water park with large numbers of bathers, contamination of the water with pathogens is likely and cannot be controlled with disinfection. Both Cryptosporidium and Giardia are easily spread through recreational water venues because of 1) their low infectious dose; 2) the huge number of Cryptosporidium oocysts and Giardia cysts that a single infected person can shed; 3) the extended period after clinical recovery from the illnesses during which oocysts and cysts can be passed in the stool; 4) the moderate chlorine-resistance of Giardia and the high chlorine-resistance of Cryptosporidium; and 5) the prevalence of improper pool maintenance.9
In summer 2002, the CDC reported that inspections of over 22,000 pools found that 54% had at least one health violation. Most violations were in wading pools, which are used by younger children including those in diapers; therapy pools; and hotel/motel pools.16 Currently, the federal government provides no oversight of chlorinated swimming venues, and no national standards exist for pool or water park design, construction, and maintenance. Pool and water park operators manage pools and spray parks with little public health oversight and few inspections.9,16
Don’t count on chlorine
Swimmers need to be aware that even if they “smell chlorine,” the water is not always safe and that chlorination will not work instantly on all microbes. Nurses can help dispel the myths about chlorination and raise awareness about recreational water illnesses. They can pass the information on to patients and parents of ill children and can learn more in a CDC program called “Healthy Swimming” (http://www.cdc.gov/healthyswimming
). The CDC recommends the following to stop transmission of diarrheal illnesses from pools and water parks:9
If you have diarrhea, wait for two weeks after it resolves before entering pools, spas, interactive fountains, lakes, rivers, or the ocean.
* Don’t swallow water in pools, spas, or interactive fountains and try to avoid getting water in your mouth.
* Take a shower before entering a pool and wash your hands after using the toilet or changing diapers.
* Take your children on bathroom breaks and check diapers often.
* Change diapers in a bathroom or diaper-changing area, not at poolside on lounge chairs or tables.
* Wash your children thoroughly (especially their bottoms) with soap and water before swimming.
The best defense against Cryptosporidium and Giardia is to prevent the pathogens from getting into water. By following CDC recommendations, visits to water parks and swimming can continue to be among the most popular recreational activities in the country.
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