An Outbreak of Cryptosporidiosis in a Public Swimming Pool Lionel Lim, MBBS, MPH (1) Prathibha Varkey, MD, MPH (1) Pete Giesen, MS (2) Larry Edmonson, MPH (2) (1) Division of preventive and occupational medicine Mayo Clinic, Rochester (2) Departments of disease prevention and control and environmental health, Olmsted County Public Health Services

Acknowledgements Olmsted County Public Health Rich Peter, MS Scott Fryer, RS Interviewers at OCPHS University of Minnesota Jeff Bender DVM, MS (formerly with the Minnesota Department of Health)

Outline 1. Features of Cryptosporidiosis 2. An outbreak case: investigation & intervention 3. Public health implications

Cryptosporidiosis Fecal-oral transmission Ingestion of small quantities of oocysts GI tract of host Incubation period < 2 weeks Peak incidence in 1 to 5 year-olds

Cryptosporidiosis Symptoms Laboratory diagnosis Stool specimens Acid-fast staining methods Immunofluorescent microscopy Treatment No effective pharmacotherapy Supportive treatment

Outbreak Case Olmsted County, MN May 6, 1998 Mother reported child with diarrhea - banquet on April 26 Similar illness in others 16/40 banquet attendees interviewed had diarrhea Case control study was done

Results of case control study Median duration of illness = 10 days Foodborne outbreak ruled out No banquet food associated with illness Persons ill prior to banquet = 5 Illness among banquet employees = 0 Illness among subsequent banquet = 0 All ill persons swam at pool X !

Subsequent Investigation Interviews of people who used pool X Stool specimens obtained from ill persons Swimming pool inspected Case Definition: Any individual who swam in pool X and experienced diarrhea for > 3 days

Interview Results 206 persons interviewed 68 excluded (had gastrointestinal symptoms that did not meet case definition of > 3 days of diarrhea) 138 remaining: 26 met case definition of illness (Attack rate of 19%)

Symptom Profile of Cases 100% 81% 77% 12% 11%

Symptom profile of cases Duration of illness Range: 3 to 28 days Median: 9 days

Stool Test Results 4 confirmed cases of Cryptosporidium : 3 from OCHPHS 1 from local health provider

Cases according to swim groups at pool X

Epidemiologic curve

Swimming Pool X

Pool Water/Filter Results Review of operation records No lapses noted Free chlorine levels adequate Cryptosporidium absent Pool water Filter material

Cryptosporidium transmission in the swimming pool Cryptosporidium not easily detected poor sensitivity of water and filter testing outbreaks still occur in absence of oocysts Resistance to chlorination MacKanzie et al. Epidemiology and Infection 1995;115: Haas. Journal of Food Protection 2000;63: MMWR 2000;50:

Germ Inactivation Time for Chlorinated Water* CDC 2003

Outbreak interventions Swimming pool Superchlorinated to 60 ppm x 24 hours 9x recommended CT* of 9600 Re-circulated throughout system Pool equipment disinfected Hallways & dressing room floors washed with 40:5 bleach solution *CT = Concentration of free chlorine (ppm) x Time (min)

OCPHS recommendations Press release to public to reduce risk of continued transmission Information given to pool operators describing outbreak and ways to prevent additional cases Public notice to not use pools up to 2 weeks following diarrhea

Public Health Implications for Health Providers Challenges: Testing for Cryptosporidiosis not routinely performed (1/10) Inadequate history Self-limiting diarrhea w/o treatment Assumptions about testing Patients with diarrhea not discouraged from swimming

Public Health Implications for Health Providers Cryptosporidium is the 3rd commonest parasite recovered from patients < 13 years When to test? Stool sampling recommended if index of suspicion Children with diarrhea Exposure to recreational water? > 3 days? Lally & Woolfrey. Pediatric Infectious Diseases Journal 1988;7:

Public Health Implications for Health Providers Benefits of testing Allows patient education Early recognition of outbreaks Prompt implementation of preventive measures

Public Health Implications for S wimming Pool Operators Cryptosporidium oocysts not easily removed by conventional sand filters Fine-grade diatomaceous earth filtration system preferred Regular changing of pool filters Maintaining adequate flow of pool water through filters Prompt treatment of fecal accidents

Public Health Implications for Swimming Pool Users Challenges Ill persons often do not seek health care for diarrheal illness (10/26) Lack of awareness: Ill or recovering persons continue to use pools

Public Health Implications for Swimming Pool Users Discourage: Use of pool in ill/recovering persons Ingestion of pool water Diapered infants from pool use Encourage: Showering prior to pool use Hand washing Frequent restroom breaks for children

Conclusion Maintain high index of suspicion for Cryptosporidiosis in persons with diarrhea associated with recreational water exposure Early detection & control of Cryptosporidiosis outbreaks Prevention of Cryptosporidiosis outbreaks Pool management Public education

Resources Information for swimmers, pool operators, and public health professionals about the spread of recreational water illnesses _response.htm Recommendations for responding to fecal accidents in pools