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Christopher Au-Yeung Communicable Disease Surveillance Centre

The health effects of recreational bathing: A meta-analysis of randomised exposure trials in four European countries. Christopher Au-Yeung Communicable Disease Surveillance Centre National Public Health Service for Wales. Background. Recreational bathing involves certain health risks:

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Christopher Au-Yeung Communicable Disease Surveillance Centre

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  1. The health effects of recreational bathing: A meta-analysis of randomised exposure trials in four European countries Christopher Au-Yeung Communicable Disease Surveillance Centre National Public Health Service for Wales

  2. Background • Recreational bathing involves certain health risks: • Self-limiting infections. • Irritations. • Accidents. • Effects of heat/cold/sunlight. • Guidelines for bathing water quality in Europe published by WHO (2003) and EU (2006) (mandatory). • Based on results from UK study in the early 1990s (Kay et al 1994). • Lack of data describing heath effects in EU freshwaters and Mediterranean marine waters.

  3. Epibathe is a collaborative project involving 5 EU partners and the WHO. • Commissioned by the EU, a 3-year program. • Objectives: • Produce “science support” for policy. • Evaluate the adequacy of the EC Bathing Water Directive (2006/7/EC) in protecting health. • Determine whether revisions are required. • To collect new data from EU freshwater sites (Hungary) and Mediterranean marine waters (Spain), and combine with existing data from UK and Germany.

  4. Contributions of NPHS to Epibathe • Long tracking record - involvement in original UK study. • Coordinating the design, production, and distribution of questionnaires. • Extensive data cleaning and analysis work. • Publications in scientific journals.

  5. Epibathe study sites in Hungary (left) and Spain. Methods - Location • Existing data: 9 trials at 9 sites in UK & Germany. • New Epibathe data: 8 trials at 6 sites in Hungary and Spain. • All sites complied with the EU bathing standards.

  6. Methods - Recruitment • Volunteers were recruited from nearby areas. • Enrolment interviews carried out 2-3 days before the trial. • Info on demographics, general health, and behaviour were collected via questionnaires.

  7. Methods - Fieldwork • Volunteers reported to site on trial day. • Randomly assigned to bathing / non-bathing group. • Followed by a 2nd interview. • Bathers performed normal bathing activities in designated bathing zone. • Water quality and bathing activities were closely monitored.

  8. Advertising posters and leaflets for the Spanish trials. Also advertised via TV, newspapers, radio, internet, and local public health offices (to ease suspicions).

  9. Trained staffs and students were deployed to various locations to carry out enrolment interviews 2-3 days before trial.

  10. Volunteers travelled to bathing sites by car or courtesy buses from nearby areas. Registration and randomisation at reception. Wrist bands to signify group.

  11. Trial day interview to collect info on recent health and non-water related risk factors of gastroenteritis. Optical character recognition (OCR) health questionnaires were colour-coded to avoid confusion. Hungarian version for Hungary, Spanish and Catalonian versions for Spain.

  12. Tributary The Hungarian trial sites were typical river beaches in the country. All bathing sites were divided into 6 zones. Shallow water area reserved for families with children. Bathing sites in Spain (left) and Hungary (above).

  13. Bathing activities monitored and recorded by supervisors. Bathers bathed in 1 of the 6 zones for 10mins, plus 3 head immersions. Water samples collected every 15mins.

  14. Entertainment for non-bathers. Face painting Astrology Football Rock climbing Sumo wrestling Hungarian volunteers collecting their “Epibathe t-shirt”. Pack lunches were provided (and microbiologically tested) to eliminate food as a possible confounder for gastroenteritis.* *Refers only to food consumed on bathing day.

  15. Methods – Follow-up • Info on disease symptoms collected at 3rd interview 1wk after trial. • Then again via postal questionnaire 3wks after trial. • Health outcome* - • Gastroenteritis (GI) – main focus. • Acute febrile respiratory illnesses (AFRI). • Ear/eye/skin ailments. *Self-reported, 1wk or 3wks after trial.

  16. Water samples tested for enterococci and E. coli (faecal indicator organisms). • Personal exposure levels assigned to bathers according to bathing time and zone. • Individuals excluded from analysis - • Chronic illnesses related to outcome of interests. • Reported GI, AFRI, ear/eye/skin symptoms on 2nd interview (bathing day). • Incomplete questionnaires.

  17. Volunteers signing up (In person / via internet) 1st interview (2-3 days before trial) Volunteers report to bathing site 2nd interview (Trial day) Randomisation Bathers bathed 10mins + 3 head immersions Non-bathers stayed away from water 3rd interview (1 week after trial day) Postal questionnaire (3 weeks after trial day) Recruitment and follow-up procedures in Epibathe.

  18. Methods – Analytical • Meta-analysis. • Stochastic modelling / Monte-Carlo simulation.

  19. Meta-analysis - FAQ • What is meta-analysis? • Traditionally used for systematic review of published data. • Also suitable for multicentre studies based on the same methodology with individual patient data. • Combines results of all studies into a summary effect estimate. • Can summarise findings of similar studies that are individually too small to find stable results.

  20. Why use meta-analysis? • Differences between studies. • E.g. Non-bather GI rate in UK > GI rate in highest exposure group in Spain. • Combing data leads to error. • Need to compare bathers with non-bathers from the same study. • Meta-analysis produces a summary odds ratio. • The contribution of each study determined by sample size and random variations. • Forest plots allow visual examination of individual study.

  21. How was it done? • A two-stage analysis, performed by the statistical package Stata. • Logistic regression models were first created for each study site, controlled for confounders. • logOR and standard errors related to the determining factor (i.e. exposure level) were extracted from the model and used in meta-analysis. • Stata produced a summary effect estimate and a Forest plot. • Larger studies with less random variations contribute more in the analysis. • Heterogeneity between studies accounted for using random-effects meta-analysis models.

  22. Forest plot of summary odds ratios of GI in bathers compared with non-bathers.

  23. Results - Descriptive stats. • 7,741 volunteers took part. 529 excluded, 7,212 analysed. • Completion rate 93%. • 3,012 marine & 4,200 freshwater. • Bathers / non-bathers = 48% / 52%. • Age range 3 – 89yrs, mean 30yrs. • Male / Female = 49% / 51%. • 455 cases of gastroenteritis (GI).

  24. Results – Meta-analysis • Bathers v non-bathers: • Summary odds ratios of GI - • Marine = 1.39 (95% CI 1.03-1.87) • Freshwater = 1.20 (95% CI 0.88-1.62) • Excess GI risk higher in marine water.

  25. a) Marine water studies b) Freshwater studies Forest plots showing OR of GI for different water type, bathers v non-bathers. Marine water – Odds ratios (OR) of GI mostly >1, smaller 95% CI, contribution of each study was similar. Freshwater – Some OR <1, wider 95% CI. Summary OR mainly driven by German studies.

  26. Exposure levels stratified into quartiles: • Stratification by quartiles eliminates the subjectivity when choosing the cut-points. • Marine – • Positive dose-response relationship between exposure (Enterococci) and GI. • Not as pronounced when E.coli was used instead. *OR of non-bathers = 1

  27. Freshwater – • Partial positive dose-response relationship between exposure and GI. • Similar pattern for both Enterococci and E.coli. *OR of non-bathers = 1

  28. What do we know so far? • Recreational bathing is associated with GI, even in compliant beaches. • The excess risk was higher in marine sites. • Risk of GI increases with elevated exposure levels. But how do we transcribe these findings into absolute magnitude for risk assessment??

  29. Risk assessment (marine water) • Using Monte-Carlo simulation to generate 10,000 random entries with a range of exposure values. • Distribution based on real Enterococci data from 11,000 EU beaches. • From Epibathe we know the GI background rates (5.0 – 9.5 per 100). • We also know the excess GI risks at different exposure levels. • A series of “risks” were estimated.

  30. From Epibathe - Mean GI risk attributable to bathing in EU marine waters with a 95th percentile of 200 Enterococci = 4.5%. • Comparable with the 5% attributable risk guideline levels of WHO (level B) and EU (good). • No evidence to suggest that the current Guideline is in need of revision. • Results will be published by the WHO shortly.

  31. But how about freshwater?? • There is insufficient data to generate a similar model. • However we know the excess risk is less marked than marine water exposure. • Freshwater quality guideline level is less stringent (currently at 2:1 with marine).

  32. Epibathe partners • University of Wales, Aberystwyth. • National Institute for Environmental Health, Hungary. • University of Rovira and Virgili, Spain. • National Public Health Services for Wales. • University of East Anglia. • World Health Organization.

  33. Thank you very much. christopher.au-yeung@nphs.wales.nhs.uk http://www.epibathe.eu

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