1. The challenge of Cryptosporidium and swimming pools
Dr Rachel Chalmers Director, Cryptosporidium Reference Unit
Public Health Wales Microbiology
Singleton Hospital
Swansea
The challenge of Cryptosporidium and swimming pools

2. The problems
The parasite
The pool
The people

3. What is Cryptosporidium?
Protozoan parasite: single celled animal
4 to 6µm in size
Life cycle occurs in the gut:
no multiplication in environment
Massive numbers of oocyst stage shed in faeces: robust and resistant
Infectious dose: amount needed to cause disease is LOW
ONE oocyst could cause illness

4. Cryptosporidium oocysts under the microscope
modified Ziehl-Neelsen Auramine Phenol Immunofluorescent
stain stain microscopy
Scanning electron micrograph of infectious sporozoites emerging from an oocyst

5. What is cryptosporidiosis?
“An illness caused by Cryptosporidium and characterized by diarrhoea, abdominal cramps, loss of appetite, low-grade fever, nausea, and vomiting”.
Especially common in children
Can be prolonged and life-threatening in severely immunocompromised patients; management of high risk patients is especially difficult due to lack of proven treatment regimes.
427 otherwise healthy people with Cryptosporidium diarrhoea
96% also had abdominal pain
65% also had vomiting, especially the children
30% appeared to recover then symptoms returned
Average (mean) duration of illness 12.7 days
14% hospitalised for 1 to 9 d (mean 3 d) (Hunter et al., EID 2004)

6. Cryptosporidiosis
Incubation period = time between exposure to the parasite and becoming ill
3-12 days, usually 5-7 days
Symptoms:
can be prolonged, lasting for up to a month
relapse, in over a third of cases.
Parasite may continue to be shed in faeces after symptoms have have stopped

7. Sources of Cryptosporidium in human infection
Two main species cause human disease:
C. parvum and C. hominis
C. parvum
C. hominis
Anthroponotic and zoonotic cycles
Anthroponotic cycle

8. Routes of transmission
DIRECT
(faecal-oral route):
Person to person spread
Contact with animals or their faeces
INDIRECT
(contamination route):
Contaminated food / water (drinking or recreational)
Contaminated objects

9. Transmission High potential for spread from infected hosts
Multiple sources (farm animals; wild animals; humans)
Multiple transmission routes
Oocysts survive ……..
Resistance to common disinfection (e.g. chlorine)
Multi-barrier approach: protection from contamination and treatment to remove it

10. Some patients highly vulnerable e.g. young children, immunocompromised
Limited treatment options
Potential for large-scale outbreaks

11. Cryptosporidium outbreaks in England and Wales 1992 to 2008 (HPA data)
Outbreak cause
Number of outbreaks
RECREATIONAL WATER - SWIMMING POOL 59
DRINKING WATER - PUBLIC SUPPLY 25
ANIMAL CONTACT 24
CHILDCARE 10
UNKNOWN 6
RECREATIONAL WATER - WATER FEATURE 3
FOODBORNE THEN PERSON TO PERSON 2
RECREATIONAL WATER - LAKE RIVER CANAL
RECREATIONAL WATER - PADDLING POOL 1
DRINKING WATER - PRIVATE WATER SUPPLY
DRINKING WATER - UNKNOWN
FOODBORNE
MILK PASTEURISATION FAILURE
Grand Total
136

12. Pool related outbreaks 1988-2012 (HPA data)

13. Focus on 2012: outbreak settings
Breakdown of pool settings:
6 at Leisure centres
3 at Holiday or caravan parks
1 at a Hydrotherapy pool in a hospital, being used for baby and toddler swimming lessons

14. Swimming pool outbreak epidemiology (Chalmers et al
Swimming pool outbreak epidemiology (Chalmers et al., Report to DWI, 2000)
Most outbreaks are in summer/autumn
Mainly linked to learner, toddler or leisure pools
High child : adult case ratio

15. Contributory factors in outbreaks of cryptosporidiosis at swimming pools
Young children (Cryptosporidium common & defecation frequent); Baby and toddler management (nappy changing facilities, swim pants)
Healthy bathers infected
People with diarrhoea continuing to use pools
Bather load (may challenge filters)
Filtration efficiency (e.g. type of filter & flocculent; maintenance; backwashing procedures)
Secondary disinfection (e.g. UV) absent or not working
Pool circulation (dead legs, shallow leisure pools, water features, surfaces with low flow areas)
Inappropriate response to faecal accidents
Management (breakdown in control of systems)

16. Swimming pool treatment: disinfection
no effective residual against Cryptosporidium
additional treatments e.g. UV, ozone, are progressive, in the plant room
Pathogen
Chlorine survival* 1mg/L, pH7.5, 25oC
E. coli O157
< 1 min
Giardia
45 min
Cryptosporidium
10.6 days
*Source

17. Swimming pool treatment: filtration
Swimming pool filtration was designed to provide a physically clean, clear and safe environment, not specifically to remove Cryptosporidium
Small size (oocysts 4-6µm)
Require low or medium rate filters with coagulation
As the filtration rate increases the log removal rate decreases:
Suggested log removal ratings for swimming pool filters (Gregory, 2002)
Filtration rate m/h
10-14
20-24
30-34
40+
Good coagulation 3
1.8
1.25
0.95
No coagulation
0.25
0.15
1.00
0.08
We must keep Cryptosporidium out of the pool to help prevent outbreaks

18. The people
Pool users
Children <5 years have highest incidence of cryptosporidiosis
Those most likely to shed oocysts, have a faecal accident….and get cryptosporidiosis
Oocyst shedding
106 to 107 oocysts per gram faeces during acute infection
Shed for 2 weeks after symptoms cease
A study in Wales showed 8% (upper 95% CI 15%) cases used swimming pools while infected (Sarah Jones, pers. comm)
Carriage (asymptomatic shedding) 1.3% children in daycare nurseries (Davies et al. 2009)
Pool water consumption
Estimate: children 6-18 years average consumption is 37ml (Dufour et al. 2006)

19. Example: a child with cryptosporidiosis poops in the pool
50 million oocysts per ml of poop X 150 mls poop = million oocysts into the pool.
In a typical 25x12m pool (450m3) that would be an average concentration of oocysts per litre or
20 oocysts per ml.
Estimate children 6-18 years average consumption is 37ml or
740 oocysts.

20. Risk
If Cryptosporidium contaminates a swimming pool, bathers are at risk of infection.
The size of that risk depends on:
the design and construction of the pool
effectiveness of the treatment
management and operation of the pool
actions taken following incidents such as faecal accidents.
Larger pools present a potentially bigger risk public health risk, but may have better treatment and operational procedures

21. Keeping Cryptosporidium out of the pool
Implement a clear policy for recognising, reporting and dealing with faecal accidents
Parents must be encouraged to adopt practices which will limit the chances of faecal contamination
People with diarrhoea must not swim in swimming pools; people with cryptosporidiosis must not swim for 2 weeks AFTER the symptoms stop
Strategies to educate users 21

22. Overview of prevention
Good design and construction to prevent cross connections and spread of contamination
Adequate filtration to remove Cryptosporidium oocysts
There is a need for secondary treatment i.e. UV at swimming pools to prevent Cryptosporidium infection
Everyone needs to recognise the health risks:
bathers, operators, managers, designers, constructors etc.