Air pollution and child respiratory health: a case-crossover study in Australia and New Zealand.

Rationale: The strength of the association between outdoor air pollution and hospital admissions in children has not yet been well defined.
Objectives: To estimate the impact of outdoor air pollution on respiratory morbidity in children after controlling for the confounding effects of weather, season, and other pollutants.
Methods: The study used data on respiratory hospital admissions in children (three age groups: < 1, 1-4, and 5-14 years) for five cities in Australia and two in New Zealand. Time series of daily numbers of hospital admissions were analyzed using the case-crossover method; the results from cities were combined using a random-effects meta-analysis.
Measurements and Main Results: Significant increases across the cities were observed for hospital admissions in children for pneumonia and acute bronchitis (0, 1-4 years), respiratory disease (0, 1-4, 5-14 years), and asthma (5-14 years). These increases were found for particulate matter with a diameter less than 2.5 microm (PM2.5) and less than 10 microm (PM10), nephelometry, NO2, and SO2. The largest association found was a 6.0% increase in asthma admissions (5-14 years) in relation to a 5.1-ppb increase in 24-hour NO2.
Conclusions: This study found strong and consistent associations between outdoor air pollution and short-term increases in childhood hospital admissions. A number of different pollutants showed significant associations, and these were distinct from any temperature (warm or cool) effects.