OBJECTIVE

To determine whether changes in 24-hour average background ozone (O₃), nitrogen dioxide (NO₂), carbon monoxide (CO) and particulates < 10 μm (PM₁₀) increase the risk of hospital emergency department (ED) presentations for asthma among children.

DESIGN, SETTING AND SUBJECTS: A time-stratified case-crossover method was used to analyse data of 603 children and young adults aged 0-19 years who were resident in a south-west metropolitan area of Perth, Western Australia, and who had presented with asthma at any public ED within Perth between 1 January 2002 and 31 December 2006. Effect sizes were assessed in relation to age group, sex and season of exposure. City-wide background air pollution was estimated from air monitoring network data.

MAIN OUTCOME MEASURES

ED presentation with asthma.

RESULTS

Patients 0-4 years with 1-day lagged exposure to NO₂ and CO showed the most significant risk of ED presentation for asthma. An interquartile range (IQR) increase in NO₂ resulted in an odds ratio (OR) of 1.70 (95% CI, 1.08-2.69). An IQR increase in CO resulted in an OR of 1.40 (95% CI, 1.06-1.84).

CONCLUSIONS

The effect sizes observed in this study were higher than those of past studies, and indicated that children aged 0-4 years were the most vulnerable to the effects of air pollution. The period of exposure most clinically relevant is the day before ED presentation.