Ambient particulate pollution and the world-wide prevalence of asthma, rhinoconjunctivitis and eczema in children: Phase One of the International Study of Asthma and Allergies in Childhood (ISAAC)

Objectives: To investigate the effect of ambient particulate matter
on variation in childhood prevalence of asthma, rhinoconjunctivitis
and eczema. Methods: Prevalences 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 residential PM10 obtained from a World Bank model.
Associations were investigated using binomial regression adjusting
for GNP per capita and for clustering within country. For countries
with more than one centre, a two stage meta-analysis was carried
out. 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 various outcomes. For severe wheeze in
13-14-year-olds, the OR for a 10 μg/m³ increase in PM₁₀ was 0.92
(95 CI 0.84 to 1.00). In 24 countries with more than one centre,
most summary estimates for within-country associations were weakly
positive. For severe wheeze in 13-14-year-olds, the summary OR for
a 10 μg/m³ increase in PM₁₀ was 1.01 (0.92 to 1.10). This result
was close to a summary OR of 0.99 (0.91 to 1.06) obtained from
published multi-centre studies. Conclusions: Modelled estimates of
particulate matter at city level are imprecise and incomplete
estimates of personal exposure to ambient air pollutants.
Nevertheless, our results together with those of previous
multi-centre 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.