Short-term effects of ozone air pollution on ischemic stroke occurrence: a case-crossover analysis from a 10-year population-based study in Dijon, France.

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, NO2, 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: We collected 493 large artery infarcts, 397 small artery infarcts, 530 cardio-embolic infarcts, 67 undeterminate infarcts, 371 transient ischemic attacks and 220 hemorrhagic strokes. For single-pollutant model and for a 10 mg/m3 increase of O3 exposure , we observed an positive association only in men, over 40 years of age, between ischemic 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 hemorrhagic 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 ischemic strokes of large arteries (p = 0.02) and for transient ischemic attacks (p = 0.01). Moreover, we found an exposure-response relationships between O3 exposure and ischemic stroke (test for trend, p = 0.01). We also observed an increase of the association in men with several cardiovascular risk factors (smoker, dyslipidemia, and hypertension). Conclusions: These observational data argue for an association between ischemic stroke occurrence and O3 pollution levels. But these results still need to be confirmed by other studies.