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Contamination in Pools Reduces Chlorine Effectiveness

July 6, 1999 (Updated 4:06pm July 8, 1999)

Contact: Dr. James Trout
United States Department of Agriculture
(301) 504-8496

ATLANTA—Contamination of swimming pools by fecal matter from leaky diapers dramatically reduces the ability of chlorine to kill the waterborne parasite Cryptosporidium, according to an article in the current issue of Emerging Infectious Diseases, CDC's peer-reviewed journal, which tracks new and reemerging infectious diseases worldwide.

This parasite has recently caused numerous outbreaks in recreational water, such as swimming pools and water parks, which are often visited by young children who are still in diapers. The infectious form of the parasite is small and highly resistant to chlorine, so standard filtering and chlorination may not be effective.

The authors of this article tested water that had fecal matter added to simulate a common "fecal accident" in a swimming pool. Results showed that levels of chlorine known to kill the parasite were no longer adequate if there was fecal matter contaminating the water, indicating that the human waste protected the parasite from chlorine inactivation.

To prevent outbreaks of diarrhea caused by this parasite, the authors suggest changes in pool engineering, such as improved filtering and more frequent turnover of the water pumped into the pool. They also suggest changes in pools' policies and urge that staff of and visitors to public pools and water parks be educated about ways to prevent waterborne disease transmission, such as 1) staying out of the pool while ill with diarrhea, 2) not swallowing pool water, 3) using safe diaper changing and handwashing practices, 4) giving young children frequent bathroom breaks, and 5) encouraging swimmers to shower before entering a pool.

For more information, contact Dr. James Trout at 301-504-8496. Access the full article at All material in Emerging Infectious Diseases is in the public domain and may be used without special permission; proper citation, however, is appreciated.

For more information on this or related topics, see

  1. Waterborne Cryptosporidiosis Threat Addressed
  2. Genetic Polymorphism Among Cryptosporidium parvum Isolates: Evidence of Two Distinct Human Transmission Cycles
  3. Cryptosporidiosis: An Emerging, Highly Infectious Threat

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