A POSSIBLE ROLE OF HIGH IMPACT WEATHER EVENTS IN WATERBORNE DISEASE OUTBREAKS IN CANADA, 1975–2001

Abstract

ISEE-236 Introduction: An adequate supply of safe water is vital to the health and wellbeing of Canadians. Awareness of the risks associated with a contaminated water supply have been heightened by recent outbreaks of Escherichia coli O157:H7, Campylobacter , and Cryptosporidium. Aim: The objectives of this research were to describe the incidence and distribution of waterborne disease outbreaks in Canada in relation to preceding weather conditions and to test the association between high impact weather events and waterborne disease outbreaks. Methods: We examined extreme rainfall and spring snowmelt in association with 168 Canadian waterborne disease outbreaks between 1975 and 2001, using case-crossover methodology. Explanatory variables including accumulated rainfall, air temperature, and peak stream flow were used to determine the relationship between high impact weather events and the occurrence of waterborne disease outbreaks. Results: We found that both total maximum degree-days above 0°C and maximum accumulated rainfall percentile were associated with risk of outbreak. For each degree-day above 0°C, the relative odds of an outbreak increased by a factor of 1.007 (95% confidence interval [CI] = 1.002– 1.012). We dichotomized maximum accumulated rainfall percentile and found an increased risk at the 93rd percentile. For rainfall events greater than the 93rd percentile, the relative odds of an outbreak increased by a factor of 2.283 (95% [CI] = 1.216–4.285). Conclusion: These results suggest that warmer temperatures and extreme rainfall are contributing factors to waterborne disease outbreaks in Canada and that this could have implications for water management and public health initiatives.