Satellite-based Estimates of Ambient Air Pollution and Global Variations in Childhood Asthma Prevalence

H Ross Anderson, Barbara K. Butland, Aaron van Donkelaar, Michael Brauer, David P. Strachan, Tadd Clayton, Rita van Dingenen, Markus Amann, Bert Brunekreef, Aaron Cohen, Frank Dentener, Christopher Lai, Lok N. Lamsal, Randall V. Martin, ISAAC Phase One and Phase Three study groups

Background: The effect of ambient air pollution on global variations and trends in asthma prevalence is unclear.

Objectives: To investigate community-level associations between asthma prevalence data from the International Study of Asthma and Allergies in Childhood (ISAAC) and satellite-based estimates of particulate matter with aerodynamic diameter <2.5 m (PM2.5) and nitrogen dioxide (NO2), and modelled estimates of ozone.

Methods: We assigned satellite-based estimates of PM2.5 and NO2 at a spatial resolution of 0.1? x 0.1? and modelled estimates of ozone at a resolution of 1? x 1? to 183 ISAAC centres. We used centre-level prevalence of severe asthma as the outcome and multilevel models to adjust for gross national income (GNI) and centre- and country-level sex, climate and population density. We examined associations (adjusting for GNI) between air pollution and asthma prevalence over time in centres with data from ISAAC Phase One (mid-1900s) and Phase Three (2001 2003).

Results: For the 13-14 year age group (128 centres in 28 countries) the estimated average within-country change in centre-level asthma prevalence per 100 children per 10% increase in centre-level PM2.5 and NO2 was -0.043 (-0.139, 0.053) and 0.017 (-0.030, 0.064) respectively. For ozone the estimated change in prevalence per ppbV was -0.116 (-0.234, 0.001). Equivalent results for the 6-7 year age-group (83 centres in 20 countries) though slightly different were not significantly positive. For the 13-14 year age-group, change in centre-level asthma prevalence over time per 100 children per 10% increase in PM2.5 from Phase One to Phase Three was -0.139 (-0.347, 0.068). The corresponding association with ozone (per ppbV) was -0.171 (-0.275, -0.067).

Conclusions: In contrast to reports from within-community studies of individuals exposed to traffic pollution we did not find evidence of a positive association between ambient air pollution and asthma prevalence as measured at the community level.

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