Heat and health in Adelaide, South Australia: assessment of heat thresholds and temperature relationships.

BACKGROUND Climate change projections have highlighted the need for public health planning for extreme heat. In Adelaide, South Australia, hot weather is characteristic of summer and heatwaves can have a significant health burden. This study examines the heat thresholds and temperature relationships for mortality and morbidity outcomes in Adelaide. METHODS Daily maximum and minimum temperatures, daily mortality, ambulance call-outs, emergency department (ED) presentations and hospital admissions were obtained for Adelaide, between 1993 and 2009. Heat thresholds for health outcomes were estimated using an observed/expected analysis. Generalized estimating equations were used to estimate the percentage increase in mortality and morbidity outcomes above the threshold temperatures, with adjustment for the effects of ozone (O(3)) and particulate matter<10 μm in mass median aerodynamic diameter (PM(10)). Effect estimates are reported as incidence rate ratios (IRRs). RESULTS Heat-related mortality and morbidity become apparent above maximum and minimum temperature thresholds of 30 °C and 16 °C for mortality; 26 °C and 18 °C for ambulance call-outs; and 34 °C and 22 °C for heat-related ED presentations. Most health outcomes showed a positive relationship with daily temperatures over thresholds. When adjusted for air pollutants, a 10 °C increase in maximum temperature was associated with a 4.9% increase in daily ambulance call-outs (IRR 1.049; 95% CI 1.027-1.072), and a 3.4% increase in mental health related hospital admissions (IRR 1.034; 95% CI 1.009-1.059) for the all-age population. Heat-related ED presentations increased over 6-fold per 10 °C increase in maximum temperature. Daily temperatures were also associated with all-cause and mental health related ED presentations. Associations between temperature over thresholds and daily mortality and renal hospital admissions were not significant when adjusted for ozone and PM(10); however at extreme temperatures mortality increased significantly with increasing heat duration. CONCLUSIONS Heat-attributable mortality and morbidity are associated with elevated summer temperatures in Adelaide, particularly ambulance call-outs, mental health and heat-related illness.

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