Outdoor air pollution and incidence of ischemic and hemorrhagic stroke: a small-area level ecological study.
OBJECTIVE
Evidence linking outdoor air pollution and incidence of stroke is limited. We examined effects of outdoor air pollution on the incidence of ischemic and hemorrhagic stroke at the population level focusing on middle-aged and older people.


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 occurring in a defined geographical area in south London (948 census output areas) where road traffic contributes to spatial variation in air pollution. Population-weighted averages were calculated for output areas using outdoor nitrogen dioxide and PM(10) concentrations modeled at a 20-m resolution.


RESULTS
There were 1832 ischemic and 348 hemorrhagic strokes in 1995 to 2004 occurring among a resident population of 267 839. Mean (SD) concentration was 25.1 (1.2) μg/m(3) (range, 23.3-36.4 μg/m(3)) for PM(10) and 41.4 (3.0) μg/m(3) (range, 35.4-68.0 μg/m(3)) for nitrogen dioxide. For ischemic stroke, adjusted rate ratios per 10-μg/m(3) increase, for all ages, 40 to 64 and 65 to 79 years, respectively, were 1.22 (0.77-1.93), 1.12 (0.55-2.28), and 1.86 (1.10-3.13) for PM(10) and 1.11 (0.93-1.32), 1.13 (0.86-1.50), and 1.23 (0.99-1.53) for nitrogen dioxide. For hemorrhagic stroke, the corresponding rate ratios were 0.52 (0.20-1.37), 0.78 (0.17-3.51), and 0.51 (0.12-2.22) for PM(10) and 0.86 (0.60-1.24), 1.12 (0.66-1.90), and 0.78 (0.44-1.39) for nitrogen dioxide.


CONCLUSIONS
Although there was no significant association between outdoor air pollutants and ischemic stroke incidence for all ages combined, there was a suggestion of increased risk among people aged 65 to 79 years. There was no evidence of increased incidence in hemorrhagic stroke.
Public Health GIS Unit, School of Health and Related Research, University of Sheffield, Regent Court, 30 Regent Street, Sheffield S1 4DA, UK. r.maheswaran@sheffield.ac.uk
Ravi
R
Maheswaran
Tim
T
Pearson
Nigel C
NC
Smeeton
Sean D
SD
Beevers
Michael J
MJ
Campbell
Charles D
CD
Wolfe
D000328:Adult; D000368:Aged; D000393:Air Pollutants / Q000009:adverse effects*; D000397:Air Pollution / Q000009:adverse effects*; D002545:Brain Ischemia / Q000453:epidemiology* / Q000209:etiology; D005260:Female; D006801:Humans; D015994:Incidence; D020300:Intracranial Hemorrhages / Q000453:epidemiology* / Q000209:etiology; D008297:Male; D008875:Middle Aged; D017062:Small-Area Analysis; D020521:Stroke / Q000453:epidemiology* / Q000209:etiology
D000393:Air Pollutants