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Recreational water use caused some cryptosporidiosis outbreaks
In 2006, 18 cryptosporidiosis outbreaks were reported, compared with five outbreaks reported for 2003 and seven for 2004.
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Although not yet final, 2006 data indicate 18 cryptosporidiosis outbreaks have been reported to the CDC’s U.S. Waterborne Disease and Outbreak Surveillance System, compared with five outbreaks reported for 2003 and seven for 2004. Data is not yet final for 2005 and 2006.
The Morbidity and Mortality Weekly Report study results described five laboratory-confirmed cryptosporidiosis outbreaks in 2006 that involved public recreational water use. Cryptosporidium oocysts are resistant to chlorine disinfection and can survive for days in treated recreational water venues despite adherence to recommended residual chlorine levels, according to the researchers.
Cryptosporidium has become the leading cause of gastroenteritis outbreaks associated with treated recreational water venues, according to the CDC. Of the recreational water venues that were inspected for disinfection and chlorination, all but one had records indicating adherence to recommended residual chlorine levels.
Colorado
After attending a birthday party at a Douglas County community water park, several people reported experiencing gastroenteritis.
All 21 party attendees were surveyed using an internet-based questionnaire. Twelve people (57%) reported diarrhea, vomiting or abdominal cramps. All seven of the stool samples collected contained Cryptosporidium, and all four of the samples tested further contained the same genotype of C. hominis, indicating a human source of contamination. Twelve (71%) of the people with water exposure at the water park reported illness, compared with none of the nine people who were not exposed to water.
A water sample collected from the water park 18 days after the party did not detect Cryptosporidium. Between August and October 2006 in Douglas County, 11 cases of laboratory-confirmed cryptosporidiosis were reported.
Illinois
Two brothers that attended a private day camp facility with a swimming pool and also participated in a day camp outing to a community water park were diagnosed with cryptosporidiosis.
The researchers conducted a study among 165 day-camp attendees, staff members and volunteers. Fifty-six (53%) of the 105 people interviewed reported diarrhea or vomiting. Seven of eight stool samples collected contained Cryptosporidium; all four of the samples tested further contained the same genotype of C. hominis. Fifty-six (89%) of the 63 people who entered the day camp swimming pool reported illness compared with none of the 39 people who did not enter the pool. Forty-one (85%) of the 48 people with water exposure at the water park reported illness compared with 15 (28%) of the 54 people who were not exposed to water.
Testing determined that the water park was positive for C. parvum but negative for C. hominis. Between July and August 2006 in Tazewell County, seven cases of laboratory-confirmed cryptosporidiosis were reported, all from the day camp.
Louisiana
Between July and August 2006, 35 cases of laboratory-confirmed cryptosporidiosis were reported to the Louisiana Office of Public Health from Ascension and East Baton Rouge parishes.
The researchers conducted a study of 35 case-patients, 29 of which were interviewed by telephone. Twenty-nine controls were selected randomly from the Louisiana Immunization Registry database and matched to the case-patients by age and location. The 29 interviewed case-patients reported diarrhea (100%), abdominal cramps (62%) and vomiting (45%).
Recreational water use at one commercial water park was the only exposure significantly associated with cryptosporidiosis, but no samples were collected from the water park because it had already closed for the season.
South Carolina
During 2006, 123 cases of laboratory-confirmed cryptosporidiosis were reported to the South Carolina Department of Health and Environmental Control.
In the Charleston region, 88 laboratory-confirmed cases were reported. Eighty-one (95%) of the 85 patients who reported in this region between June and November 2006 were interviewed by telephone.
Multiple water parks, swimming pools and day care centers were identified as common sources of exposure. As a result, health department staff members visited eight of the identified recreational water venues and 13 of the identified day care centers to examine policies and implement control measures. A water sample collected from one water park tested negative for Cryptosporidium.
Wyoming
Between June and October 2006, 34 cases of laboratory-confirmed cryptosporidiosis were reported to the Wyoming Department of Health from Campbell and Crook counties.
The researchers conducted a study of 29 patients, with 26 of the 29 interviewed by telephone. Forty-one unmatched controls were enrolled from among people who were not ill and were seeking routine preventive care at a local public health nursing office. The 26 interviewed case-patients reported diarrhea (92%), vomiting (56%), and abdominal cramps (54%).
A water sample collected from one public pool tested negative for Cryptosporidium. The largest public swimming pool in the two-county region was hyperchlorinated.
Prevention and education
Adoption of improved disinfection technologies that inactivate Cryptosporidium and increased public awareness of healthy swimming practices may reduce transmission of Cryptosporidium in treated recreational water venues.
In-line ultraviolet radiation or ozone systems can enhance the level of protection for swimmers by decreasing the duration of oocyst transmission. CDC officials recommend that further risk reduction be achieved through use of increased circulation flow rates, flocculants, remedial biocidal shock treatments and occupancy-dependent water replacement.
Public education should reinforce the message that swimming pool patrons share responsibility for controlling the spread of Cryptosporidium in recreational water venues and encourage the public to be proactive regarding prevention of illness, according to the researchers.
Messages should stress refraining from swimming while ill with diarrhea, not swallowing pool water, practicing good hygiene and reporting fecal contamination to pool operators so that appropriate disinfection can be administered.
A multifaceted approach for prevention of cryptosporidiosis in treated water venues must address operational, technological and behavioral factors related to recreational water use, according to the study. A national program to develop a model aquatic health code and risk-reduction plan has been initiated by the CDC and partners in the public health and aquatic sectors.
“The popularity of recreational water venues, the number and geographic distribution of recent cryptosporidiosis outbreaks, and the resistance of Cryptosporidium to chlorination suggest that treatment strategies for recreational water facilities need to be improved,” the researchers wrote.
For more information:
- CDC. Cryptosporidiosis outbreaks associated with recreational water use – five states, 2006. MMWR. 2007;56:729-732.
- Additional information is available at www.cdc.gov/healthyswimming.