Abstract
BACKGROUND: The effect of ambient air pollution on global variations and trends in asthma prevalence is unclear.
OBJECTIVES: Our goal was 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 mu 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 degrees x 0.1 degrees and modeled estimates of ozone at a resolution of 1 degrees x 1 degrees to 183 ISAAC centers. We used center-level prevalence of severe asthma as the outcome and multilevel models to adjust for gross national income (GM) and center- and country-level sex, climate, and population density. We examined associations (adjusting for GNI) between air pollution and asthma prevalence over time in centers with data from ISAAC Phase One (mid-1900s) and Phase Three (2001-2003).
RESULTS: For the 13- to 14-year age group (128 centers in 28 countries), the estimated average within-country change in center-level asthma prevalence per 100 children per 10% increase in center-level PM2.5 and NO2 was -0.043 [95% confidence interval (Cl): 0.139, 0.053] and 0.017 (95% Cl: 0.030, 0.064) respectively. For ozone the estimated change in prevalence per parts per billion by volume was -0.116 (95% Cl: -0.234, 0.001). Equivalent results for the 6- to 7-year age group (83 centers in 20 countries), though slightly different, were not significantly positive. For the 13- to 14-year age group, change in center-level asthma prevalence over time per 100 children per 10% increase in PM2.5 from Phase One to Phase Three was -0.139 (95% Cl: -0.347, 0.068). The corresponding association with ozone (per ppbV) was -0.171(95% Cl: -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.