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CMAJ Open. 2016 Feb 2;4(1):E48-58. doi: 10.9778/cmajo.20150111. eCollection 2016 Jan-Mar.

Assessment of the effect of cold and hot temperatures on mortality in Ontario, Canada: a population-based study.

Author information

1
Public Health Ontario (Chen, Wang, Li, Copes); Dalla Lana School of Public Health (Chen, Foty, Villeneuve, Copes), University of Toronto, Toronto, Ont.; Institute for Clinical Evaluative Sciences (Chen), Toronto, Ont.; Climate Change and Health Office (Yagouti), Health Canada; Air Health Science Division (Lavigne), Health Canada; Department of Epidemiology and Community Medicine (Lavigne), University of Ottawa, Ottawa, Ont.; Sick Kids Hospital (Foty), Toronto, Ont.; Population Studies Division (Burnett, Cakmak), Health Canada; Department of Health Sciences (Villeneuve), Carleton University, Ottawa, Ont.

Abstract

BACKGROUND:

Ambient high temperature is associated with death; however, heat-related risk of death has not been quantified systematically in Ontario, the most populous province in Canada. Less is known about cold-related risk in this population. Our objective was to quantify the health impact from cold and hot temperatures in Ontario.

METHODS:

The study population consisted of all residents of Ontario who died between Jan. 1, 1996, and Dec. 31, 2010, from any nonaccidental cause. A case-crossover analysis was applied to assess the relation between daily temperature fluctuation and deaths from nonaccidental and selected causes in cold (December-February) and warm (June-August) seasons, respectively, adjusting for various potential confounders. Risk estimates were obtained for each census division, then pooled across Ontario. We examined potential effect modification for selected comorbidities and sociodemographic characteristics.

RESULTS:

In warm seasons, each 5°C increase in daily mean temperature was associated with a 2.5% increase in nonaccidental deaths (95% confidence interval [CI] = 1.3% to 3.8%) on the day of exposure (lag 0). In cold seasons, each 5°C decrease in daily temperature was associated with a 3.0% (95% CI 1.8% to 4.2%) increase in nonaccidental deaths, which persisted over 7 days (lag 0-6). The cold-related effects (lag 0-6) were stronger for cardiovascular-related deaths (any cardiovascular death: 4.1%, 95% CI 2.3% to 5.9%; ischemic heart disease: 5.8%, 95% CI 3.6% to 8.1%), especially among people less than 65 years of age (8.0%, 95% CI 3.0% to 13.0%). Conversely, heat most strongly increased respiratory-related deaths during admission to hospital (26.0%, 95% CI 0% to 61.4%). Across Ontario, each 5°C change in daily temperature was estimated to induce 7 excess deaths per day in cold seasons and 4 excess deaths in warm seasons.

INTERPRETATION:

Heat contributed to excess deaths in Ontario, although the effect of cold weather appeared to be greater. Further work is required to better define high-risk subgroups, which might include the homeless and people with inadequately heated housing.

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