BACKGROUND Very few published studies have looked at the effects of air pollution on health in the primary care setting. As part of a large study to examine the association between air pollution and a number of health outcomes, the relationship between daily GP consultations for asthma and other lower respiratory diseases (LRD) and air pollution in London was investigated.

RESULTS Positive associations, weakly significant and consistent across lags, were observed between asthma consultations and nitrogen dioxide (NO₂) and carbon monoxide (CO) in children and particulate matter of less than 10 μm in diameter (PM₁₀) in adults, and between other LRD consultations and sulphur dioxide (SO₂) in children. A consistently negative association with ozone in children was observed in both disease categories. The effect estimates of most pollutants were much larger when analysed separately by season, particularly in the children: percentage change in asthma consultations during the warm season (April-September) for a 10–90th percentile increase in 24 hour NO₂ lagged by one day = 13.2% (95% CI 5.6 to 21.3), with CO = 11.4% (95% CI 3.3 to 20.0), and with SO₂ = 9.0% (95% CI 2.2 to 16.2). In adults the only association consistent over different lag periods was with PM₁₀ = 9.2% (3.7 to 15.1). The associations of pollution and consultations for LRD were increased mainly in the winter months: percentage change in consultations by children in winter with NO₂ = 7.2% (95% CI 2.8 to 11.6), CO = 6.2% (95% CI 2.3 to 10.2), and SO₂ = 5.8% (95% CI 1.6 to 10.2).

CONCLUSIONS There are associations between air pollution and daily consultations for asthma and other lower respiratory disease in London. The most significant associations were observed in children and the most important pollutants were NO₂, CO, and SO₂. In adults the only consistent association was with PM₁₀.