Exposure to bushfire smoke and asthma: an ecological study.

OBJECTIVE To examine the relationship between the mean daily concentration of respirable particles arising from bushfire smoke and hospital presentations for asthma. DESIGN AND SETTING An ecological study conducted in Darwin (Northern Territory, Australia) from 1 April - 31 October 2000, a period characterised by minimal rainfall and almost continuous bushfire activity in the proximate bushland. The exposure variable was the mean atmospheric concentration of particles of 10 microns or less in aerodynamic diameter (PM(10)) per cubic metre per 24-hour period. OUTCOME MEASURE The daily number of presentations for asthma to the Emergency Department of Royal Darwin Hospital. RESULTS There was a significant increase in asthma presentations with each 10-microg/m(3) increase in PM(10) concentration, even after adjusting for weekly rates of influenza and for weekend or weekday (adjusted rate ratio, 1.20; 95% CI, 1.09-1.34; P < 0.001). The strongest effect was seen on days when the PM(10) was above 40 microg/m(3) (adjusted rate ratio, 2.39; 95% CI, 1.46-3.90), compared with days when PM(10) levels were less than 10 microg/m(3). CONCLUSION Airborne particulates from bushfires should be considered as injurious to human health as those from other sources. Thus, the control of smoke pollution from bushfires in urban areas presents an additional challenge for managers of fireprone landscapes.