Background: Short-term changes in levels of fine ambient particulate matter (PM2.5) may increase the risk of acute ischemic stroke; however, results from prior studies have been inconsistent. We examined this hypothesis using data from a multicenter prospective stroke registry.
Methods: We analyzed data from 9202 patients hospitalized with acute ischemic stroke, having a documented date and time of stroke onset, and residing within 50 km of a PM2.5 monitor in 8 cities in Ontario, Canada. We evaluated the risk of ischemic stroke onset associated with PM2.5 in each city using a time-stratified case-crossover design, matching on day of week and time of day. We then combined these city-specific estimates using random-effects meta-analysis techniques. We examined whether the effects of PM2.5 differed across strata defined by patient characteristics and ischemic stroke etiology.
Results: Overall, PM2.5 was associated with a −0.7% change in ischemic stroke risk per 10-μg/m3 increase in PM2.5 (95% confidence interval = −6.3% to 5.1%). These overall negative results were robust to a number of sensitivity analyses. Among patients with diabetes mellitus, PM2.5 was associated with an 11% increase in ischemic stroke risk (1% to 22%). The association between PM2.5 and ischemic stroke risk varied according to stroke etiology, with the strongest associations observed for strokes due to large-artery atherosclerosis and small-vessel occlusion.
Conclusions: These results do not support the hypothesis that short-term increases in PM2.5 levels are associated with ischemic stroke risk overall. However, specific patient subgroups may be at increased risk of particulate-related ischemic strokes.
From the aNational University of Ireland, Galway, Ireland; bInstitute for Clinical Evaluative Sciences, Toronto, Ontario, Canada; cBeth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA; dDepartment of Medicine, University of Toronto and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada; and eCenter for Environmental Health and Technology, Department of Community Health, Brown University, Providence, RI.
Submitted 22 February 2010; accepted 9 November 2010; posted 11 March 2011.
The Registry of the Canadian Stroke Network is funded by grants from the Canadian Stroke Network and the Ontario Ministry of Health and Long-term Care, and is based at the Institute for Clinical Evaluative Sciences, which is also supported by an operating grant from the Ontario Ministry of Health and Long-Term Care.
M.K. is supported by the Canadian Stroke Network, the University Health Network Women's Health Program and holds a New Investigator Award from the Canadian Institutes of Health Research.
Supported by the National Institute of Environmental Health Sciences (NIEHS) (grants ES015774, ES017125, and ES009825).
The contents of this report are solely the responsibility of the authors and do not necessarily represent the official vies of the sponsoring institutions.
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Correspondence: Martin O'Donnell, HRB Clinical Research Facility, Geata an Eolais, National University of Ireland, Galway, Ireland. E-mail: firstname.lastname@example.org.