Effect of temperature on mortality during the six warmer months in Sydney, Australia, between 1993 and 2004

Studies of heat-related mortality have been predominantly based on analyses of underlying cause of death as the single indicator of a population's vulnerability to high temperatures. Examination of both underlying and associated causes of death could provide a more comprehensive understanding of the population at risk. This study analyzes the impact of high temperatures on mortality in Sydney, Australia, during the warmer six months (October-March) between 1993 and 2004, using the underlying and associated cause of death due to all-cause, circulatory, and respiratory disease. Some mortality datasets were also divided into two age groups, 0-64 and 65+. A generalized linear model assuming negative binomial distribution was constructed for the daily mortality counts using daily maximum temperature and hourly maximum concentrations of ozone (O₃) and particulate matter (PM₁₀) as covariates. With the air pollution terms in a model, the change in mortality was estimated to be between 4.5% and 12.1% for a 10 °C increase in maximum daily temperature, depending on mortality dataset. When air pollutants were removed from a model, the above mortality percentages changed by -1.1% to 0.9%. When both underlying and associated causes of death were considered, the effect remained the same or became lower. Maximum temperature has been found to have a significant effect on mortality in Sydney, with PM₁₀ and O₃ confounding the association.