Transcript An Outbreak of Cryptosporidiosis in a Public Swimming Pool

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
Symptom Profile of Cases
Muscle aches
11%
Sweats/chills
11%
Fever
12%
Headache
12%
77%
Nausea
Abdominal cramps
81%
100%
Diarrhea
0
5
10
15
20
Number of cases
25
30
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
Group Swimming #
Median Cases Exposure to
activity
interviewed age
(%)
pool water 
A
Competitive 26
14
16 (61) +++
B
Preschool
18
2
7 (39) ++
C
Children
61
9
2 (3)
++
D
Water
22
61 (29) 1 (4)
0
aerobics*
E
Lap
8
79
0
+
F
Causal
3
16
0
+
All
138
14
26 (19)
 Exposure based on frequency of pool use and probability of water ingestion
* One 29-year old adult from water aerobics group participated in other
swimming activities
Epidemiologic curve
D = Water aerobics (1)
8
C = Children (2)
7
No. of Cases
6
A
B = Preschool (7)
A
A = Competitive (16)
5
A
4
A A
3
C
2
OCPHS Notified
Pool Closes
A A B
C
B
B
B b A
A A A
1
B
0
A A A A B
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2
April
Olmsted County Public Health Services
Date of onset
A D
3
4
Bb
5
6 7
May
8
9 10 11 12 13 14
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;115:545-553
Haas. Journal of Food Protection 2000;63:827-831
MMWR 2000;50:406-410
Germ Inactivation Time for
Chlorinated Water*
Germ
Time
E. coli O157:H7
Bacterium
Hepatitis A
Virus
Giardia
Parasite
Cryptosporidium
Parasite
Less than 1 minute
about 16 minutes
about 45 minutes
about 9600 minutes
(6.7 days)
* 1ppm (1mg/L) chlorine at pH 7.5 and 77°F
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;7:200-201
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
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
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:
Encourage:
• Use of pool in
• Showering prior to
ill/recovering
persons
• Ingestion of pool
water
• Diapered infants
from pool use
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
• 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