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Presented by Kate Thomas

A possible role of high impact weather events in waterborne disease outbreaks in Canada, 1975-2001. Presented by Kate Thomas. M. Kate Thomas 1 , Dominique Charron 2 , David Waltner-Toews 1 , Corinne Schuster 3 Abdel R. Maarouf 4 and John D. Holt 1 1. University of Guelph, Ontario

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Presented by Kate Thomas

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  1. A possible role of high impact weather events in waterborne disease outbreaks in Canada, 1975-2001 Presented by Kate Thomas M. Kate Thomas1, Dominique Charron2, David Waltner-Toews1, Corinne Schuster3 Abdel R. Maarouf4 and John D. Holt1 1. University of Guelph, Ontario 2. Public Health Agency of Canada, Guelph, Ontario 3. HPRP Project, Climate change effects on waterborne disease risk in Canada, University of Guelph 4. Environment Canada, Toronto, Ontario

  2. Outline • Introduction • Study Objectives • Data • Methodology • Results • Discussion

  3. Introduction • Safe water is of great concern to everyone • Global need to determine what factors play a role in waterborne disease outbreaks • Potential impact of weather on waterborne disease outbreaks • Canada’s climate is changing with the potential for more variable weather and weather extremes

  4. Study Objectives • To describe the incidence and distribution of waterborne disease outbreaks in Canada and high impact weather events occurring prior to an outbreak • To test the association between high impact weather events and waterborne disease outbreaks

  5. Data ~ Outbreaks • Waterborne disease outbreak: • 2 or more cases of disease, occurring at the same place and the same time, linked to a drinking water supply • 1975 through 2001 in Canada • 168 in total • 58 Definite • 34 Probable • 76 Possible 92 Outbreaks

  6. Data ~ Exposure variables • High Impact Weather Event: • Short term weather event that contributes high volumes of water and causes substantial overland flow

  7. Data ~ Exposure variables • Meteorological stations • Daily rainfall, maximum and minimum temperature • As geographically close as possible by latitude and longitude co-ordinates • Rainfall (mm) • Maximum of rolling 5-day cumulative average amount • Maximum percentile • Timing • Temperature (oC days) • Total maximum degree days above 0 oC • Maximum of rolling 5-day cumulative average amount • Timing

  8. Data ~ Exposure variables • Stream flow stations • Daily stream flow • As geographically close as possible by latitude and longitude co-ordinates • Stream flow (m3/s) • Maximum of rolling 5-day cumulative average amount • Maximum percentile • Timing • Stream flow peak • Outbreaks January – May • Amount of maximum peak • Percentile of maximum peak • Timing of peak

  9. Data ~ Exposure variables • Ecozone map • Ecozone map is overlaid with map of outbreaks • Canada is divided into 15 terrestrial ecozones based on soil type, vegetation, climate and landforms • Categorical variable to control interaction between soil type and other explanatory variables

  10. Methodology • Case-Crossover study design1 • Designed for acute events with transient exposures • Event = Waterborne Disease Outbreak • Exposure = High Impact Weather Event • Individual = Community / Well System experiencing outbreak • Hazard Time Period = 6 weeks 1. Maclure, Malcolm. The case-crossover design: A method for studying transient effects on the risk of acute events. Am J Epidemiol 1991;133:144-53

  11. 1975 1980 1985 1990 1995 2000 2001 C C C X C 1975 1976 1977 1978 1979 1980 Methodology • Time-stratified case-crossover • Within each stratum one year is the case (X) the other 4 are controls (C)

  12. Results

  13. Results

  14. Results • Final Model Relative odds of an Outbreak = exp [ 1(total maximum degree-days above 0 oC) + 2 (accumulated rainfall 93rd percentile) + jIj ] • Where Ij are indicator variables for year effects and the jare the corresponding parameters

  15. Results • Accumulated rainfall 93rd percentile • OR=2.28311 (95% CI = 1.21644 – 4.28512) • Total maximum degree days above 0 oC • OR=1.00672 (95% CI = 1.00166 -1.01181)

  16. Results

  17. Discussion • Cumulative impact of total maximum degree days above 0 oC is substantial • Novel use of Case-Crossover study design • Significant association between extreme rainfall and waterborne disease outbreaks • Adds to body of literature on weather and waterborne disease • Provides Canadian perspective

  18. Acknowledgements • Dominique Charron • David Waltner-Toews • Abdel Maarouf • John Holt • Corinne Schuster • Health Policy Research Program • Public Health Agency of Canada (formerly Health Canada) • Environment Canada • Dave Harvey, Don MacIver, Heather Auld, Joan Klaassen • Department of Population Medicine, University of Guelph • ECCHO team www.eccho.ca

  19. Thank you Any Questions?

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