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 microns (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). 

CONCLUSION: 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.