An Outbreak of Cryptosporidiosis in a Public Swimming Pool

1
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

2
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)

3
Outline

• Features of Cryptosporidiosis
• An outbreak case investigation intervention
• Public health implications

4
Cryptosporidiosis

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

5
Cryptosporidiosis

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

6
Outbreak CaseOlmsted 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

7
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 !

8
Subsequent Investigation

• Case Definition
• Any individual who swam in pool X and experienced
  diarrhea for gt 3 days

9
Interview Results

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

10
Symptom Profile of Cases
11
11
12
12
77
81
100
11
Symptom profile of cases

• Duration of illness
• Range 3 to 28 days
• Median 9 days

12
Stool Test Results

• 4 confirmed cases of Cryptosporidium
• 3 from OCHPHS
• 1 from local health provider

13
Cases according to swim groups at pool X
14
Epidemiologic curve
15
Swimming Pool X
16
Pool Water/Filter Results

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

17
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
1995115545-553 Haas. Journal of Food
Protection 200063827-831 MMWR 200050406-410
18
Germ Inactivation Time for Chlorinated Water
CDC 2003
19
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 405
  bleach solution

CT Concentration of free chlorine (ppm) x Time
(min)
20
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

21
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

22
Public Health Implications for Health Providers

• Cryptosporidium is the 3rd commonest parasite
  recovered from patients lt 13 years
• When to test?
• Stool sampling recommended if index of suspicion
• Children with diarrhea
• Exposure to recreational water?
• gt 3 days?

Lally Woolfrey. Pediatric Infectious Diseases
Journal 19887200-201
23
Public Health Implications for Health Providers

• Benefits of testing
• Allows patient education
• Early recognition of outbreaks
• Prompt implementation of preventive measures

24
Public Health Implications for Swimming 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

25
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

26
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

27
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

28
Resources

• http//www.cdc.gov/healthyswimming/
• Information for swimmers, pool operators, and
  public health professionals about the spread of
  recreational water illnesses
• http//www.cdc.gov/healthyswimming/fecal_response.
  htm
• Recommendations for responding to fecal accidents
  in pools