Objectives: To investigate the role of ambient particulate matter in explaining international variations in the prevalence of asthma, rhinoconjunctivitis and eczema in children.
Methods: The prevalence of symptoms and diagnoses of asthma, rhinoconjunctivitis and eczema obtained in Phase One of the International Study of Asthma and Allergies in Childhood (ISAAC) were matched with city-level estimates of particulate matter with aerodynamic diameter < 10µm (PM10) obtained from a World Bank model. Associations were investigated using a binomial regression model which adjusted for Gross National Product per capita and for clustering within country. For countries with more than one centre a two stage meta-analysis was done. The results were compared with a meta-analysis of published multi-centre studies.
Results: Annual concentrations of PM10 at city level were obtained for 105 ISAAC centres in 51 countries. After controlling for GNP per capita, there was a weak negative association between PM10 and the various outcomes. For severe wheeze in the 13-14 year age group, the odds ratio for a 10 µg/m3 increase in PM10 was 0.92 (95% CI 0.84,1.00). In 24 countries with more than one centre, most of the summary estimates for within-country associations were weakly positive. For severe wheeze in the 13-14 year age group, the summary odds ratio for a 10 µg/m3 increase in PM10 was 1.01 (0.92,1.10). This result was close to a summary odds ratio of 0.99 (0.91,1.06) obtained from published multi centre studies.
Conclusions: Modelled estimates of PM at city level will necessarily be imprecise and incomplete estimates of personal exposure to ambient air pollutants. Nevertheless, the results of this world-wide ecological analysis, together with those of previous multicentre studies, suggest that urban background PM10 has little or no association with the prevalence of childhood asthma, rhinoconjunctivitis or eczema either within or between countries.
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