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The challenge of Cryptosporidium and swimming pools

The challenge of Cryptosporidium and swimming pools. Dr Rachel Chalmers Director, Cryptosporidium Reference Unit Public Health Wales Microbiology Singleton Hospital Swansea. The problems. The parasite The pool The people. What is Cryptosporidium ?.

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The challenge of Cryptosporidium and swimming pools

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  1. The challenge of Cryptosporidium and swimming pools Dr Rachel ChalmersDirector, 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. 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 Routes of transmission

  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)

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

  17. Swimming pool treatment: filtration Suggested log removal ratings for swimming pool filters (Gregory, 2002) • 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: • 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 faecesduring 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 = 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.

  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. 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

  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.

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