1. 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 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 Introduction Study Objectives Study Objectives Data Data Methodology Methodology Results Results Discussion Discussion

3. Introduction Safe water is of great concern to everyone Safe water is of great concern to everyone Global need to determine what factors play a role in waterborne disease outbreaks Global need to determine what factors play a role in waterborne disease outbreaks Potential impact of weather on waterborne disease outbreaks Potential impact of weather on waterborne disease outbreaks Canadas climate is changing with the potential for more variable weather and weather extremes Canadas 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 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 To test the association between high impact weather events and waterborne disease outbreaks

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

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

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

8. Data ~ Exposure variables Stream flow stations Stream flow stations Daily stream flow Daily stream flow As geographically close as possible by latitude and longitude co- ordinates As geographically close as possible by latitude and longitude co- ordinates Stream flow (m 3 /s) Stream flow (m 3 /s) Maximum of rolling 5-day cumulative average amount Maximum of rolling 5-day cumulative average amount Maximum percentile Maximum percentile Timing Timing Stream flow peak Stream flow peak Outbreaks January – May Outbreaks January – May Amount of maximum peak Amount of maximum peak Percentile of maximum peak Percentile of maximum peak Timing of peak Timing of peak

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

10. Methodology Case-Crossover study design 1 Case-Crossover study design 1 Designed for acute events with transient exposures Designed for acute events with transient exposures Event = Waterborne Disease Outbreak Event = Waterborne Disease Outbreak Exposure = High Impact Weather Event Exposure = High Impact Weather Event Individual = Community / Well System experiencing outbreak Individual = Community / Well System experiencing outbreak Hazard Time Period = 6 weeks 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. Methodology Time-stratified case-crossover Time-stratified case-crossover 1975198019851990199520012000 197519761977197819791980 CXCCC Within each stratum one year is the case (X) the other 4 are controls (C) Within each stratum one year is the case (X) the other 4 are controls (C)

12. Results

13. Results

14. Results Relative odds of an Outbreak = exp [ 1 (total maximum degree-days above 0 o C) + 2 (accumulated rainfall 93 rd percentile) + j I j ] Where Where I j are indicator variables for year effects and the j are the corresponding parameters Final Model Final Model

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

16. Results Average max temp (6-week) 20 o C 25 o C Total maximum degree-day above 0 o C 8401050 Relative odds of outbreak 277.531132.74 Impact of 5 o C increase in temp Over a 4-fold increase in relative odds of outbreak

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

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

19. Thank you Any Questions?