Background: Little research has investigated the health effects of particulate exposure from bushfires (also called wildfires, biomass fires, or vegetation fires), and these exposures are likely to increase, for several reasons. We investigated associations of daily mortality and hospital admissions with bushfire-derived particulates, compared with particulates from urban sources in Sydney, Australia from 1994 through 2002.
Methods: On days with the highest particulate matter (PM)10 concentrations, we assumed PM10 was due primarily to bushfires. We calculated the contribution of bushfire PM10 on these days by subtracting the background PM10 concentration estimated from surrounding days. We assumed PM10 on the remaining days was from usual urban sources. We implemented a Poisson model, with a bootstrap-based methodology, to select optimum smoothed covariate functions, and we estimated the effects of bushfire PM10 and urban PM10, lagged up to 3 days.
Results: We identified 32 days with extreme PM10 concentrations due to bushfires or vegetation-reduction burns. Although bushfire PM10 was consistently associated with respiratory hospital admissions, we found no consistent associations with cardiovascular admissions or with mortality. A 10 μg/m3 increase in bushfire PM10 was associated with a 1.24% (95% confidence interval = 0.22% to 2.27%) increase in all respiratory disease admissions (at lag 0), a 3.80% (1.40% to 6.26%) increase in chronic obstructive pulmonary disease admissions (at lag 2), and a 5.02% (1.77% to 8.37%) increase in adult asthma admissions (at lag 0). Urban PM10 was associated with all-cause and cardiovascular mortality, as well as with cardiovascular and respiratory hospital admission, and these associations were not influenced by days with extreme PM10 concentrations.
Conclusions: PM10 from bushfires is associated primarily with respiratory morbidity, while PM10 from urban sources is associated with cardiorespiratory mortality and morbidity.
From the aNorthern Rivers University, Department of Rural Health, University of Sydney, New South Wales, Australia; bNorth Coast Area Health Service, New South Wales, Australia; cEnvironmental Health Branch, New South Wales Health Department, Sydney, Australia; dCentre for Epidemiology and Research, New South Wales Health Department, New South Wales, Australia; eCentre for Research, Evidence Management and Surveillance, Sydney South West Area Health Service, and School of Public Health and Community Medicine, University of New South Wales, Australia; fCenter for Urban Epidemiologic Studies, New York Academy of Medicine, New York, NY; gWestern Sydney Area Health Service, and School of Public Health, University of Sydney, Sydney, Australia; and hDepartment of Biostatistics, University of Washington, Seattle, WA.
Submitted 20 May 2008; accepted 1 April 2009; posted 10 November 2009.
Supported by the Australian Research Council Linkage Grant (LP0882048), SPIRT Grant (2049570), and the New South Wales Department of Health Biostatistical Officer Training Program (to D.L., A.A., and B.K.).
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Correspondence: Geoff Morgan, Northern Rivers University, Department of Rural Health, University of Sydney, PO Box 3074, Lismore, New South Wales 2480, Australia. E-mail: email@example.com.