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Background: As heatwaves are expected to be more frequent, longer, and more intense in the future, it is imperative to understand how heatwaves affect health. However, it is intensely debated about how a heatwave should be defined., Objectives: This study explored the possibility of developing a health risk-based definition for heatwave, and assessed the heat-related mortality in the three largest Australian cities., Methods: Daily data on climatic variables and non-accidental deaths for Brisbane, Melbourne and Sydney during the period 1988-2009 were obtained from relevant government agencies. Several local heatwave definitions were tested by using percentiles (e.g., from the 75th to 99th centile) of mean temperature with duration ≥2 days across these cities. We examined the relative risks of mortality associated with heatwaves in each city using Poisson generalised additive model, after controlling for long-term trend, within-season variation, day of the week, and relative humidity. Then, Bayesian hierarchical model with segment-spline was used to examine the threshold for the heatwave-related impacts., Results: A consistent and significant increase in mortality during heatwaves was observed in all three cities. The pooled data show that the relative risk of mortality started to increase around the 95th centile of temperature, increased sharply at the 97th centile and rose alarmingly at the 99th centile. Based on research findings, we proposed tiered health risk-based metrics to define a heatwave., Conclusions: Our findings provide supportive evidence for developing health risk-based metrics to assess the impacts of heatwave. These findings may have important implications for assessing and reducing the burden of heat-related mortality., (Crown Copyright © 2015. Published by Elsevier Inc. All rights reserved.)

Objectives: To assess the heterogeneity of heatwave-related impacts on mortality across different cities., Design: A multicity time series study., Setting: 3 largest Australian cities: Brisbane, Melbourne and Sydney., Participants: All residents living in these cities., Main Outcome Measures: Non-external causes mortality data by gender and two age groups (ie, 0-75 and 75+) for these cities during the period 1988-2009 were obtained from relevant government agencies., Results: Total mortality increased mostly within the same day (lag 0) or a lag of 1 day (lag 1) during almost all heatwaves in three cities. Using the heatwave definition (HWD) as the 95th centile of mean temperature for two or more consecutive days in the summer season, the relative risk for total mortality at lag 1 in Brisbane, Melbourne and Sydney was 1.13 (95% CI 1.08 to 1.19), 1.10 (95% CI 1.06 to 1.14) and 1.06 (95% CI 1.01 to 1.10), respectively. Using the more stringent HWD-the 99th centile of mean temperature for two or more consecutive days, the relative risk of total mortality at the lags of 0-2 days in Brisbane and Melbourne was 1.40 (95% CI 1.29 to 1.51) and 1.47 (95% CI 1.36 to 1.59), respectively. Elderly, particularly females, were more vulnerable to the impact of heatwaves., Conclusions: A consistent and significant increase in mortality was observed during heatwaves in the three largest Australian cities, but the impacts of heatwave appeared to vary with age, gender, the HWD and geographical area.

Background: Heat-related impacts may have greater public health implications as climate change continues. It is important to appropriately characterize the relationship between heatwave and health outcomes. However, it is unclear whether a case-crossover design can be effectively used to assess the event- or episode-related health effects. This study examined the association between exposure to heatwaves and mortality and emergency hospital admissions (EHAs) from non-external causes in Brisbane, Australia, using both case-crossover and time series analyses approaches., Methods: Poisson generalised additive model (GAM) and time-stratified case-crossover analyses were used to assess the short-term impact of heatwaves on mortality and EHAs. Heatwaves exhibited a significant impact on mortality and EHAs after adjusting for air pollution, day of the week, and season., Results: For time-stratified case-crossover analysis, odds ratios of mortality and EHAs during heatwaves were 1.62 (95% confidence interval (CI): 1.36-1.94) and 1.22 (95% CI: 1.14-1.30) at lag 1, respectively. Time series GAM models gave similar results. Relative risks of mortality and EHAs ranged from 1.72 (95% CI: 1.40-2.11) to 1.81 (95% CI: 1.56-2.10) and from 1.14 (95% CI: 1.06-1.23) to 1.28 (95% CI: 1.21-1.36) at lag 1, respectively. The risk estimates gradually attenuated after the lag of one day for both case-crossover and time series analyses., Conclusions: The risk estimates from both case-crossover and time series models were consistent and comparable. This finding may have implications for future research on the assessment of event- or episode-related (e.g., heatwave) health effects.

Background: There is no global definition of a heatwave because local acclimatisation and adaptation influence the impact of extreme heat. Even at a local level there can be multiple heatwave definitions, based on varying temperature levels or time periods. We investigated the relationship between heatwaves and health outcomes using ten different heatwave definitions in Brisbane, Australia., Methodology/principal Findings: We used daily data on climate, air pollution, and emergency hospital admissions in Brisbane between January 1996 and December 2005; and mortality between January 1996 and November 2004. Case-crossover analyses were used to assess the relationship between each of the ten heatwave definitions and health outcomes. During heatwaves there was a statistically significant increase in emergency hospital admissions for all ten definitions, with odds ratios ranging from 1.03 to 1.18. A statistically significant increase in the odds ratios of mortality was also found for eight definitions. The size of the heat-related impact varied between definitions., Conclusions/significance: Even a small change in the heatwave definition had an appreciable effect on the estimated health impact. It is important to identify an appropriate definition of heatwave locally and to understand its health effects in order to develop appropriate public health intervention strategies to prevent and mitigate the impact of heatwaves.