Cryptosporidium: Information for Swimming Pool Operators

Provided by the Centers for Disease Control and Prevention

This information is being provided to inform those who manage and operate pools, waterparks, and other venues about the risks of cryptosporidiosis and ways to help prevent it.

by Gerald M. Dworkin


Cryptosporidium parvum (also known as “Crypto”) is a parasite excreted in the feces of infected humans, cattle, and other mammals. The infectious form of the parasite (the “oocyst”) is too small to be seen without a microscope and is highly resistant to the levels of chlorine normally found in swimming pools. Infection with Cryptosporidium, known as cryptosporidiosis, often causes a profuse and watery diarrhea that is frequently accompanied by abdominal cramping. Fatigue, fever, loss of appetite, nausea, and vomiting are other signs and symptoms of crypto, which begin an average of about 7 days after oocysts are swallowed. A person with a normal, healthy immune system can expect symptoms to last for 2 weeks or less. People with weakened immune systems (those with HIV/AIDS, on cancer chemotherapy, or those receiving organ transplants) will have cryptosporidiosis for a longer period of time, and it could become life-threatening. Small children and pregnant women with cryptosporidiosis can quickly become severely dehydrated.

The infection occurs after accidental swallowing of Cryptosporidium oocysts in contaminated pool water, by drinking contaminated tap water, eating or drinking contaminated food products, or through direct contact with feces. Since 1988, health departments have documented more than 10 outbreaks of crypto at both waterparks and swimming pools in the U.S., resulting in thousands of people becoming ill after swallowing contaminated pool water. It is believed that these reported outbreaks are only the tip of the iceberg, and that outbreaks will be more frequently recognized in the coming years as health care providers increase their testing of patients for Crypto infection.

The number of Cryptosporidium oocysts needed to cause infection is probably very low; as few as 2 – 10 oocysts have been shown to cause illness in animals. At the height of infection a person is very contagious and may pass millions of infectious oocysts per day in his or her stool, enough to contaminate a large waterpark. Cryptosporidium oocysts appear in the stool of infected persons at the onset of symptoms and can continue to be excreted in the stool for several weeks after the symptoms resolve. Outside the body, oocysts may remain infectious for 2 – 6 months in a moist environment. The ability of Crypto to infect the body is probably the same for everyone. However, the severity of disease differs and may be greater in children, pregnant women, and those whose immune systems are compromised.

Cryptosporidium is highly resistant to halogen (chlorine/bromine) disinfection. This is a concern in pools where the primary protection against disease transmission is halogen disinfection. Cryptosporidium oocysts, because they are microscopic, may pass through many types of pool sand filters and most cartridge filters. A diatomaceous earth filter can capture most of the oocysts. However, even with an effective filter it may take as long as 2 1/2 days to remove most of the oocysts from a pool. More studies need to be undertaken before the effectiveness of nonhalogen liquid sanitizers and other methods of disinfection on Cryptosporidium are known. Additionally, new filter media and flocculents have not been studied to determine their effectiveness in removing Crypto oocysts.

Once a pool is contaminated (for example, through a fecal accident or by rinsing a diaper in the pool), it can remain a source of infection for pool users for prolonged periods of time because of Cryptosporidium’s resistance to halogens and the difficulty of removing oocysts by filtration. Pool operators can reduce the risk of initial contamination by using common sense operating practices.

The Centers for Disease Control and Prevention recommends the following:

  1. Prepare a plan. In the even that you get calls about crypto, how would you answer questions and complaints? To whom would you refer these individuals? How would you manage press inquiries in the event of an outbreak?
  2. Prepare and implement a written fecal accident policy for your pool. Teach this policy to all relevant employees. Be sure that employees enforce your policy. Instruct lifeguards and other personnel to monitor the pool area for fecal accidents and behavior that can put others at risk.
  3. Unfortunately, fecal accidents that are caused by Cryptosporidium infection are likely to be in the form of watery diarrhea, and therefore will probably not be seen or reported. It is therefore important to:
    • Train staff to report illnesses they experience to the management and not to swim if ill with diarrhea or abdominal cramps.
    • Develop a policy for pool usage by diaper-aged and toddler children. These children are at high risk for having fecal accidents in the pool. The best situation is one where there is a separate pool for diaper-aged children that has a separate water circulation and filtration system. In such a situation, diaper-aged children should only be allowed in the pool specifically designated for them. Older children, adolescents, and adults should not be allowed in that pool unless they are caring for a diaper-aged child. After using the “kiddie” pool, patrons should rinse off before entering the pool designated for older individuals. If a separate “kiddie” pool is not possible, strong consideration should be given to excluding diaper-aged children from the pool. The use of rubber pants or “swim diapers” have been suggested as a way to reduce fecal contamination by infants and toddlers, but these methods have not been tested to determine their ability to contain Cryptosporidium.
    • Provide signage in a conspicuous location before pool entry. The sign might state:
      1. “If you have or have had diarrhea in the past 2 weeks, please do not use the pool.”
      2. “Shower your child and yourself before entering the pool.” (Showering is very important as thousands of oocysts may reside on the surfaces near the anus after a bowel movement. The oocysts can contaminate the pool upon contact with the water. A policy of mandatory showers before swimming and enforcement of the policy can reduce the risk of remaining, unnoticeable fecal material being washed into the pool. Showering should include the thorough use of soap and warm water, focusing on the surfaces near the anus. A quick rinsing over a swimsuit with cold water will probably not do much good. Facilities should always have hot water available in bathroom and shower facilities).
      3. Maintain the recirculation and filtration equipment to provide maximum filtration. Many pools are periodically overused, and the average bather loads exceeded. These pools may need filtration equipment that exceeds required minimums just to maintain normal water quality during peak periods of use. If normal minimums are exceeded, install anti vortex drain covers (with no top openings and automatic cut-off valves) to avoid injuries to small children.
      4. Maintain the chemical feed equipment and chemicals at optimal levels. This includes maintaining the disinfectant levels; optimal pH (7.2 – 7.8); alkalinity (80 – 120 ppm); calcium hardness (200 – 400 ppm), and total dissolved solids (below 2500mg/liter). Lack of proper pH can greatly affect disinfection effectiveness in chlorinated pools. Be sure to obtain water samples for chemical and pH testing from the poolside, not the central filter bay or pumphouse. Although crypto is chlorine resistant, maintaining proper equipment and chemical levels will reduce the risk of illnesses from most other fecally transmitted pathogens. Consider scheduling pool usage by incontinent persons (e.g. infant swim classes) later in the day to allow for filtration systems to run overnight before heavy usage by other patrons.
      5. Provide training on the prevention of diseases and injuries for all persons responsible for the maintenance and operation of the swimming pool. Include in this training information regarding Cryptosporidium.
      6. Provide safe and easily accessed diaper-changing areas and discourage diaper-changing at poolside. Inspect your facility often.
      7. Use club or organization newsletters to remind patrons:
    • Toddlers should wear close fitting swimsuits or underwear in order to better contain solid or semi-solid stool.
    • Do not use the pool if you or your child has had diarrhea in the previous 2 weeks.
    • Do not change your child’s diaper at poolside.
    • Do not rinse diaper-aged children in the pool before, during, or after diaper changes.
    • Assist young children in making frequent visits to the bathroom to minimize accidents.
    • Do not rinse hands in the pool following a trip to the bathroom or changing a child’s diaper. Wash hands correctly by using soap and warm water and thoroughly cleaning all hand surfaces.
    • Notify the pool management if you or a family member develops a gastrointestinal illness that you think may have been related to a visit to the swimming pool.

Following these recommendations may help reduce the risk of Cryptosporidium contamination of your pool.

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