Temperature Sensitivity in Indigenous Australians

To the Editor:

Indigenous people face challenges that may make them more sensitive to extreme temperatures. These include poor health, inadequate infrastructure, and poverty.¹ Few studies have examined the effects of extreme temperatures on Indigenous people² or have considered the possible role of body mass in sensitivity to extreme temperatures.

In 1997, we enrolled a prospective cohort of 719 Indigenous people in a remote Aboriginal community in Australia’s Northern Territory (see the eAppendix for Materials and Methods, and Results, https://links.lww.com/EDE/A669). Hospitalization discharge diagnoses (International Classification of Diseases, Tenth Revision: A00–R99) were recorded for every participant between 1997 and 2004. Data on daily minimum temperatures were linked to hospitalization data using dates of hospitalization.

We used a time-stratified case-crossover analysis to explore associations of temperature with risk of hospitalization.³ Hotter minimum temperatures were associated with an increased risk of hospitalization for all participants, particularly for overweight people and men. Colder minimum temperatures were associated with increased risk of hospitalization for women. Both cold and hot temperatures were associated with an increased risk of hospitalization in older people (Figure).

FIGURE: Nonlinear associations between temperature and hospitalization using a case-crossover model. Temperature has a lag of 0–21 days and 4 degrees of freedom natural cubic spline. The thick lines are log odds ratios and the thin lines are 95% confidence intervals. The dotted horizontal line represents no change in risk.

We used a case-only analysis⁴ to examine susceptibility of particular groups to cold or hot temperatures (eAppendix, Figure 2 and Table 4, https://links.lww.com/EDE/A669). Overweight people were more likely than normal weight people to be hospitalized during extremely hot days but not during cold days. Similarly, men were at a greater risk of hospitalization during hot days than women. Older people had a greater risk of hospitalization during both cold and hot days (eAppendix, Figure 2 and Table 4, https://links.lww.com/EDE/A669).

Understanding who is susceptible to extreme temperatures is important in minimizing the public health impact of extreme weather. One notable result is the susceptibility of overweight people to hot but not cold temperatures. The prevalence of overweight and obesity among adult Indigenous Australians has been steadily increasing (from 51% in 1995 to 60% in 2005)⁵ as it has in many other populations.⁶

Another important finding is the much greater risk of hospitalization on hot days for men than for women. This might be caused by biological differences (eg, differences in body fat) or behavioral differences (eg, differences in clothing).⁷

Older people were clearly more sensitive to both cold and hot temperatures than younger people. This presumably reflects the declining physiological function of the elderly, whose thermal regulation system weakens with age.⁸

Overall, hot temperatures substantially increased the risk of hospitalization for Indigenous Australians. The vulnerability of this population—and specific subgroups of the population—should be taken into account in public policies dealing with the health of indigenous people.

ACKNOWLEDGMENTS

We thank the Aboriginal people who participated in this study. We thank David Ung (The Northern Territory Department of Health and Community Services) who helped obtain the hospitalization data and the weather underground website for making weather data publically available.

Yuming Guo

School of Medicine

University of Queensland

Herston, Queensland, Australia

[email protected]

Zhiqiang Wang

School of Medicine

University of Queensland

Herston, Queensland, Australia

Shanshan Li

School of Population Health

University of Queensland

Herston, Queensland, Australia

Shilu Tong

Adrian G. Barnett

School of Public Health and Social Work

Institute of Health and Biomedical Innovation

Queensland University of Technology

Kelvin Grove, Queensland, Australia