Abstract

Objective: To evaluate the association between air pollutants and the occurrence of acute stroke from 10-year population-based study.

Methods: The daily stroke count was obtained from Dijon Stroke Register between March 1994 and December 2004. The register recorded all first-ever strokes among residents of Dijon (150 000 inhabitants) in France, using standard diagnostic criteria. Pollutant concentrations (SO₂, CO, NO_2, O₃ and PM₁₀) were measured hourly. A bi-directional case-crossover design was used to examine the association between air pollutant and stroke onset. The conditional logistic regression model included the meteorological parameters (temperature, relative humidity), influenza epidemics and holidays.

Results: The authors collected 493 large artery infarcts, 397 small artery infarcts, 530 cardio-embolic infarcts, 67 undeterminate infarcts, 371 transient ischaemic attacks and 220 haemorrhagic strokes. For single-pollutant model and for a 10 mg/m³ increase of O₃ exposure, a positive association was observed only in men, over 40 years of age, between ischaemic stroke occurrence and O₃ levels with 1-day lag, (OR 1.133, 95% CI 1.052 to 1.220) and 0-day lag (OR 1.058, 95% CI 0.987 to 1.134). No significant associations were found for haemorrhagic stroke. In two-pollutant models, the effects of O₃ remained significant after each of the other pollutants were included in the model, in particular with PM₁₀. A significant association was observed for ischaemic strokes of large arteries (p = 0.02) and for transient ischaemic attacks (p = 0.01). Moreover, the authors found an exposure-response relations between O₃ exposure and ischaemic stroke (test for trend, p = 0.01). An increase in association in men with several cardiovascular risk factors (smoker, dyslipidemia and hypertension) was also observed.

Conclusion: These observational data argue for an association between ischaemic stroke occurrence and O₃ pollution levels; these results still need to be confirmed by other studies.