Research

Vegetation fire smoke, indigenous status and cardio-respiratory hospital admissions in Darwin, Australia, 1996–2005: a time-series study

Ivan C Hanigan¹ , Fay H Johnston^{* 1,2,3} and Geoffrey G Morgan^{* 4}

¹School for Environmental Research, Charles Darwin University, Ellengowan Drive, Darwin, 0909, Northern Territory, Australia

²Menzies School of Health Research, Charles Darwin University, Ellengowan Drive, Darwin, 0909, Northern Territory, Australia

³Menzies Research Institute, University of Tasmania, Private Bag 23 Hobart 7001, Tasmania, Australia

⁴North Coast Area Health Service and Department of Rural Health (Northern Rivers) University of Sydney, 55–61 Uralba Street, Lismore, 2480, New South Wales, Australia

author email corresponding author email* Contributed equally

Environmental Health 2008, 7:42doi:10.1186/1476-069X-7-42

Published:	5 August 2008

Abstract

Background

Air pollution in Darwin, Northern Australia, is dominated by smoke from seasonal fires in the surrounding savanna that burn during the dry season from April to November. Our aim was to study the association between particulate matter less than or equal to 10 microns diameter (PM₁₀) and daily emergency hospital admissions for cardio-respiratory diseases for each fire season from 1996 to 2005. We also investigated whether the relationship differed in indigenous Australians; a disadvantaged population sub-group.

Methods

Daily PM₁₀ exposure levels were estimated for the population of the city from visibility data using a previously validated model. We used over-dispersed Poisson generalized linear models with parametric smoothing functions for time and meteorology to examine the association between admissions and PM₁₀ up to three days prior. An interaction between indigenous status and PM₁₀ was included to examine differences in the impact on indigenous people.

Results

We found both positive and negative associations and our estimates had wide confidence intervals. There were generally positive associations between respiratory disease and PM₁₀ but not with cardiovascular disease. An increase of 10 μg/m³ in same-day estimated ambient PM₁₀ was associated with a 4.81% (95%CI: -1.04%, 11.01%) increase in total respiratory admissions. When the interaction between indigenous status and PM₁₀ was assessed a statistically different association was found between PM₁₀ and admissions three days later for respiratory infections of indigenous people (15.02%; 95%CI: 3.73%, 27.54%) than for non-indigenous people (0.67%; 95%CI: -7.55%, 9.61%). There were generally negative estimates for cardiovascular conditions. For non-indigenous admissions the estimated association with total cardiovascular admissions for same day ambient PM₁₀ and admissions was -3.43% (95%CI: -9.00%, 2.49%) and the estimate for indigenous admissions was -3.78% (95%CI: -13.4%, 6.91%), although ambient PM₁₀ did have positive (non-significant) associations with cardiovascular admissions of indigenous people two and three days later.

Conclusion

We observed positive associations between vegetation fire smoke and daily hospital admissions for respiratory diseases that were stronger in indigenous people. While this study was limited by the use of estimated rather than measured exposure data, the results are consistent with the currently small evidence base concerning this source of air pollution.