Risk factors of direct heat-related hospital admissions during the heatwave in Adelaide, Australia: a matched case–control study

Abstract:

The newly released Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report has once again confirmed the unequivocal global warming trend over the past century. In particular, it confirms that extreme heat events are very likely to happen with a higher frequency and longer duration. Australia’s climate is already changing, with significant increases in heat extremes observed since the 1960s. Australian summers in recent years have been extremely hot, including the record-breaking Australian summer of 2009, 2013 and 2014, with potentially significant public health implications.

Our study, drawing on individual data, aims to provide robust evidence on risk factors for heat-related conditions in the Australian context to support relevant policy and intervention programmes, including refining current heat and health early warning systems, and developing better individual health services that could reduce morbidity during heatwaves.

Objective

The extreme heatwave of 2009 in South Australia dramatically increased morbidity, with a 14-fold increase in direct heat-related hospitalisation in metropolitan Adelaide. Our study aimed to identify risk factors for the excess morbidity.

Design & Setting

A matched case–control study of risk factors was conducted. Patients and matched community controls were interviewed to gather data on demographics, living environment, social support, health status and behaviour changes during the heatwave.

Participants

Cases were all hospital admissions with heat-related diagnoses during the 5-day heatwave in 2009. Controls were randomly selected from communities.

Outcome measures

Descriptive analyses, simple and multiple conditional logistic regressions were performed. Adjusted ORs (AORs) were estimated.

Results

In total, 143 hospital patients and 143 matched community controls were interviewed, with a mean age of 73 years (SD 21), 96% European ethnicity, 63% retired, 36% with high school or higher education, and 8% institutional living. The regression model indicated that compared with the controls, cases were more likely to have heart disease (AOR=13.56, 95% CI 1.27 to 144.86) and dementia (AOR=26.43, 95% CI 1.99 to 350.73).

The protective factors included higher education level (AOR=0.48, 95% CI 0.23 to 0.99), having air-conditioner in the bedroom (AOR=0.12, 95% CI 0.02 to 0.74), having an emergency button (AOR=0.09, 95% CI 0.01 to 0.96), using refreshment (AOR=0.10, 95% CI 0.01 to 0.84), and having more social activities (AOR=0.11, 95% CI 0.02 to 0.57).

Conclusions

Pre-existing heart disease and dementia significantly increase the risk of direct heat-related hospitalisations during heatwaves. The presence of an air-conditioner in the bedroom, more social activities, a higher education level, use of emergency buttons and refreshments reduce the risk during heatwaves.

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