May 1996
ATLANTA — As summer temperatures draw legions of children into swimming pools, lakes, rivers and creeks, you might see more cases of gastrointestinal infections related to recreational water use.
Water used for recreation can be a mode of transmission for such diarrhea-causing microbes as Cryptosporidium, Giardia, Shigella sonnei and Escherichia coli O157:H7. Children acquire the pathogens by swallowing water. Investigators have linked recreational water use to a bevy of recent outbreaks of gastrointestinal (GI) illness.
In a two-year period during 1993 and 1994, 14 U.S. outbreaks of GI illness related to recreational water use were reported to the Centers for Disease Control and Prevention (CDC). Cryptosporidium caused six outbreaks, Giardia caused four, Shigella three and E. coli O157:H7, one.
In 1991 and 1992, the CDC received reports of 11 outbreaks of GI illness associated with recreational water use. Giardia caused four and Cryptosporidium caused two. S. sonnei caused two outbreaks and S. sonnei with E. coli O157:H7 caused another outbreak.
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Cryptosporidium caused a 1993 outbreak of GI illness involving more than 400 people in New Jersey. They were infected after swimming in a lake. Cryptosporidium also caused a swimming-related outbreak of diarrheal illness in Dane County, Wis., in the summer of 1993. The median age of the 36 people who met the outbreak case definition was 4 years old. Ages ranged from 1 year to 40 years. Most patients had watery diarrhea and stomach cramps. Investigators implicated two swimming pools as the mode of transmission. Cryptosporidium oocysts are resistant to chlorine and have a high infectivity. Investigators stated that health care providers should consider asking for Cryptosporidium testing of stool specimens from people with watery diarrhea.
In June 1992, 500 people contracted cryptosporidial illness from a wave pool at a park in Oregon.
In the summer of 1995, Shigella bacteria in a lake in a state park in Pennsylvania is believed to have caused an outbreak of diarrhea. Investigators identified 19 cultured-confirmed cases of shigellosis and suspected that many more probably were infected.
In 1991, E. coli O157:H7 and S. sonnei caused an outbreak of diarrheal illness in Blue Lake Park in Oregon, near Portland. Investigators identified 21 children who had bloody diarrhea or hemolytic uremic syndrome due to E. coli 0157:H7, and 38 people, mostly children, who had bloody diarrhea due to S. sonnei. All had been in the lake during a 24-day period.
When children present with GI illness, ask whether they have been swimming. If so, ask whether the children swam in chlorinated water, advised Dennis Juranek, VMD, of the CDC. If the child had been in a chlorinated pool, consider the possibility of infection with Cryptosporidium or Giardia.
These protozoan parasites are resistant to chlorine, noted Juranek, who is associate director of the CDC's Division of Parasitic Diseases. Chlorine usually eliminates bacterial pathogens, he said.
For suspected Cryptospordium infection, you should specifically ask your testing lab to look for the pathogen, Juranek said. Most laboratories do not test for the parasite routinely, even if a physician requests that stools be examined for ova and parasites. According to a recent CDC survey, about 95% of physicians believed that if they ask their lab to do an ova-and-parasite exam the lab will test for Cryptosporidium. The survey also revealed, however, that most labs only test for Cryptosporidium when specifically requested by the physician.
Because children with Cryptosporidium infection may have diarrhea accompanied by nausea, vomiting and fever, you might mistakenly diagnose viral gastroenteritis, Juranek said.
Obtain a stool culture to identify the diarrhea-causing organism. The results may help you decide on therapy. For example, no treatment is recommended for Cryptosporidium infection. Immunocompetent people will get well on their own, Juranek said. Metronidazole is recommended for treating Giardia infection.
Advise parents not to let toddlers with diarrhea enter swimming areas. They also should be told not to wash children who have diarrhea or to clean soiled diapers in this water, health officials advise. In the New Jersey outbreak of cryptosporidial illness, people had rinsed soiled diapers in the lake.
People do not have to defecate in water for transmission to occur. Immunocompetent people who recover from acute Cryptosporidium infection can excrete the pathogen in their stool for 30 to 60 days, Juranek said. They can have enough fecal material in their perianal area to contaminate a pool.
Investigators believe that such people were the source of two or three swimming-related outbreaks in the aftermath of the drinking-water-related outbreak in Milwaukee that resulted in more than 400,000 cases of cryptosporidial illness. Consequently, people should shower before entering a swimming pool to remove fecal matter from the perianal area, Juranek said.
Moreover, older children should be instructed to avoid toddler swimming pools because of the increased risk of fecally contaminated water, he said.
If you suspect that a recreational site is a source of illness, notify the local health department.
For more information, see:
- CDC. Surveillance for waterborne disease outbreaks — United States, 1991-1992. MMWR 1993;42:1-22.
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