Lack of association between air pollutant exposure and short-term risk of ischaemic stroke in Lyon, France Laura Mechtouff 1 *, Florence Canoui-Poitrine 2 , Anne-Marie Schott 2,3 , Norbert Nighoghossian 1 , Paul Trouillas 1 , Anne Termoz 2 , Sylvie Porthault-Chatard 4 , Jean-Stephane David 5,6 , Virginie Chasles 7 , and Laurent Derex 1 Background Some observational and experimental studies have suggested a short-term relationship between air pol- lutants and ischaemic stroke; however, the results conflict. Aims The objective of this study was to investigate the asso- ciation between particulate matter less than 2·5 and 10 microns in aerodynamic diameter, nitrogen dioxide, sulphur dioxide and ozone, and short-term risk of ischaemic stroke in Lyon, France. Methods The AVC69 study was a multicenter cohort study in which all consecutive adult patients admitted to one of the emergency or neurological departments of the Rhône area for suspicion of stroke were included during a seven-month period. Only patients with ischaemic stroke living within the study area, composed of Lyon and 18 neighbouring commu- nities with homogenous air pollutants exposure, formed the basis of our study. We adopted a time-stratified case- crossover design to analyse the short-term effect (up to two-days) of air pollutants on ischaemic stroke incidence. Models were adjusted for temperature, variation of atmos- pheric pressure, minimal relative humidity, influenza epi- demics, pollen count, and holidays. Stratified analyses by gender and class age were performed. Different lag times were analysed. Results 376 patients were included. Mean age was 76·6 years (13·7). 53·7% were women. No association was observed between air pollutants and short-term risk of ischaemic stroke after adjustment for main confounding factors. Results remained unchanged whatever the gender or age. Conclusions These results suggest a lack of association between air pollutant exposure and short-term risk of ischaemic stroke in a French urban area. Key words: air pollution, cross-over studies, particulate matter, stroke Introduction An association between air pollutants and cardiovascular morbidity and mortality was clearly demonstrated during the acute episodes of air pollution in the 1950s’ (1). Studies have examined the association between air pollutant exposure, even at levels close to or lower than current standards, and death related to stroke (2–8). Yet death poststroke can occur long after stroke onset and may be caused by non-neurological disorders. Few studies have examined the association between air pollutants and short-term risk of ischaemic stroke. Find- ings have been inconsistent, with studies concluding either a slightly positive association or none. Among air pollutants, fine particulate matter (PM), i.e. less than 2·5 microns in aerodynamic diameter (PM2·5), has emerged as a pollutant of interest. Its ultrafine fraction or soluble components can pen- etrate deeply into the pulmonary tract, pass into the blood circulation, and have direct effects on thrombosis, endothelial function, and atherosclerotic plaque growth and stability (9,10). Clarifying the role of air pollutant exposure in stroke occurrence is important, even if the extra risk is moderate, Correspondence: Laura Mechtouff*, Hospices Civils de Lyon, Stroke Center, Hôpital Pierre Wertheimer, 59 Boulevard Pinel, 69677 Lyon Bron cedex, France. E-mail: laura.mechtouff@chu-lyon.fr 1 Hôpital Pierre Wertheimer, Stroke Center, Hospices Civils de Lyon, Bron-Lyon, France 2 Pôle IMER, Hospices Civils de Lyon, Lyon, France 3 Public health division, Université Lyon 1, Lyon, France 4 Service d’Anesthésie-Réanimation-Urgence, Hospices Civils de Lyon, Lyon, France 5 Service d’Anesthésie-Réanimation-Urgence, Centre Hospitalier Lyon Sud, Hospices Civils de Lyon, Pierre Bénite, France 6 Faculté de Médecine Lyon Sud, Université Lyon 1, Oullins, France 7 EA 4129 Santé Individu Société, Université Jean Moulin Lyon 3, Lyon, France Conflicts of interests: None declared. Funding: This work was funded by a grant from the Fondation de France. The AVC69 study was funded by a grant from the French Ministry of Health (PHRC interregional 2007 ‘Etude d’observation des délais de prise en charge et des trajectories des accidents vasculaires cérébraux dans le Rhône’). DOI: 10.1111/j.1747-4949.2011.00737.x Research © 2012 The Authors. International Journal of Stroke © 2012 World Stroke Organization Vol ••, November 2012, ••–•• 1