Supplementary Material for: Estimation of Short-Term Effects of Air Pollution on Stroke Hospital Admissions in Southern Sweden

<i>Background:</i> Short-term exposure to high levels of air pollution can increase stroke risk. In this study we investigated the short-term effects of air pollution on hospital admissions for stroke in a setting where pollutant levels are rather low. We also addressed methodological issues in evaluating the short-term effects of air pollution. <i>Methods:</i> Daily admissions of ischemic (n = 11,267) and hemorrhagic (n = 1,681) stroke were obtained from a Swedish quality register for stroke, Riks-Stroke. We used two types of exposure data: (1) daily measured background levels of ozone, temperature and particles with a diameter <10 µm (PM<sub>10</sub>) and (2) modeled levels of a mixture of NO and NO<sub>2</sub> (NO<sub>x</sub>) at the residential address of each individual. <i>Results:</i> We estimated a 13% (95% confidence interval, 4–22%) increased risk for hospital admissions for ischemic stroke for levels of PM<sub>10</sub> above 30 µg/m<sup>3</sup> compared to <15 µg/m<sup>3</sup>, whereas temperature above 16°C decreased the risk. No consistent associations were found for hemorrhagic stroke or for ischemic stroke and ozone or NO<sub>x</sub>. <i>Conclusion:</i> Particulate air pollution and temperature seemed to be associated with ischemic stroke hospital admissions. Individual exposure modeling facilitates a detailed exposure assessment but may also be more prone to misclassification errors. The time series and case crossover approaches yielded similar effect estimates.