Transcript here - Ireland Active

The challenge of Cryptosporidium and swimming
pools
Dr Rachel Chalmers
Director, Cryptosporidium Reference Unit
Public Health Wales Microbiology
The challenge of Cryptosporidium
and
Singleton Hospital
swimming pools
Swansea
The problems
• The parasite
• The pool
• The people
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
Cryptosporidium oocysts under the
microscope
modified Ziehl-Neelsen Auramine Phenol
stain
stain
Immunofluorescent
microscopy
Scanning electron micrograph of
infectious sporozoites emerging from an
oocyst
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)
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
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
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
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
• Some patients highly vulnerable e.g.
young children, immunocompromised
• Limited treatment options
• Potential for large-scale outbreaks
Cryptosporidium outbreaks in England and
Wales 1992 to 2008 (HPA data)
Outbreak cause
RECREATIONAL WATER - SWIMMING POOL
DRINKING WATER - PUBLIC SUPPLY
ANIMAL CONTACT
CHILDCARE
UNKNOWN
RECREATIONAL WATER - WATER FEATURE
FOODBORNE THEN PERSON TO PERSON
RECREATIONAL WATER - LAKE RIVER CANAL
RECREATIONAL WATER - PADDLING POOL
DRINKING WATER - PRIVATE WATER SUPPLY
DRINKING WATER - UNKNOWN
FOODBORNE
MILK PASTEURISATION FAILURE
Grand Total
Number of outbreaks
59
25
24
10
6
3
2
2
1
1
1
1
1
136
Pool related outbreaks 1988-2012
(HPA data)
Focus on 2012: outbreak settings
Farm (5, C. parvum)
Enviro (1, C. parvum)
Nursery (1, C. hominis)
Food (1, C. parvum)
Pool (10, C. hominis)
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
Swimming pool outbreak epidemiology
(Chalmers et al., Report to DWI, 2000)
• Most outbreaks are in
summer/autumn
Cryptosporidium outbreaks, E&W
swimming pools 1992 to 2009
(CfI GSURV data)
• Mainly linked to learner,
toddler or leisure pools
Number of
outbreaks
15
10
5
0
Jan
• High child : adult case
ratio
Feb Mar
Apr May Jun
Jul
Month
Aug Sep Oct
Nov Dec
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)
Swimming pool treatment: disinfection
 no effective residual against Cryptosporidium
 additional treatments e.g. UV, ozone, are progressive, in
the plant room
Pathogen
E. coli O157
Giardia
Cryptosporidium
Chlorine survival*
1mg/L, pH7.5, 25oC
< 1 min
45 min
10.6 days
*Source http://www.cdc.gov/healthywater/swimming/pools/chlorine-disinfection-timetable.html
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
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)
Example: a child with cryptosporidiosis
poops in the pool
50 million oocysts per ml of poop X 150 mls
poop = 7500 million oocysts into the pool.
In a typical 25x12m pool (450m3) that would be
an average concentration of 20 000 oocysts
per litre or
20 oocysts per ml.
Estimate children 6-18 years average
consumption is 37ml or
740 oocysts.
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
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
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.