Outdoor air pollution, subtypes and severity of ischemic stroke - a small-area level ecological study

Background: Evidence linking outdoor air pollution and incidence of ischemic stroke subtypes and severity is limited. We examined associations between outdoor PM 10 and NO 2 concentrations modeled at a fine spatial resolution and etiological and clinical ischemic stroke subtypes and severity of ischemic stroke. Methods: We used a small-area level ecological study design and a stroke register set up to capture all incident cases of first ever stroke (1995 – 2007) occurring in a defined geographical area in South London (948 census output areas; population of 267839). Modeled PM 10 and NO 2 concentrations were available at a very fine spatial scale (20 meter by 20 meter grid point resolution) and were aggregated to output area level using postcode population weighted averages. Ischemic stroke was classified using the Oxford clinical classification, the Trial of Org 10172 in Acute Stroke Treatment (TOAST) etiological classification, National Institutes of Health Stroke Scale (NIHSS) score and a pragmatic clinical severity classification based on Glasgow coma score, ability to swallow, urinary continence and death