The challenge of Cryptosporidium and swimming pools

The challenge of Cryptosporidium and swimming pools

Dr Rachel ChalmersDirector, Cryptosporidium Reference Unit

Public Health Wales MicrobiologySingleton Hospital

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 Immunofluorescent

stain stain 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 ill3-12 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

C. hominis

C. parvum

Two main species cause human disease: C. parvum and C. hominis

Anthroponotic and zoonotic cycles

Anthroponotic cycle

Routes of transmissionDIRECT

(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 Number of outbreaksRECREATIONAL WATER - SWIMMING POOL 59DRINKING WATER - PUBLIC SUPPLY 25ANIMAL CONTACT 24CHILDCARE 10UNKNOWN 6RECREATIONAL WATER - WATER FEATURE 3FOODBORNE THEN PERSON TO PERSON 2RECREATIONAL WATER - LAKE RIVER CANAL 2RECREATIONAL WATER - PADDLING POOL 1DRINKING WATER - PRIVATE WATER SUPPLY 1DRINKING WATER - UNKNOWN 1FOODBORNE 1MILK PASTEURISATION FAILURE 1Grand Total 136

Pool related outbreaks 1988-2012 (HPA data)

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

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

Cryptosporidium outbreaks, E&W swimming pools 1992 to 2009

(CfI GSURV data)

0

5

10

15

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Num

ber

of

outb

reak

s

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 Chlorine survival* 1mg/L, pH7.5, 25oC

E. coli O157 < 1 min

Giardia 45 min

Cryptosporidium 10.6 days

*Source http://www.cdc.gov/healthywater/swimming/pools/chlorine-disinfection-timetable.html

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

Swimming pool treatment: filtrationSwimming 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:

• 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

• 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

Keeping Cryptosporidium out of the pool

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.