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Alana Hansen,¹ Peng Bi,¹ Monika Nitschke,² Philip Ryan,¹ Dino Pisaniello,¹ and Graeme Tucker²

¹Discipline of Public Health, School of Population Health and Clinical Practice, Faculty of Health Sciences, The University of Adelaide, Adelaide, South Australia, Australia; ²South Australian Department of Health, Adelaide, South Australia, Australia

Abstract
Objective: The goal of this study was to identify mental, behavioral, and cognitive disorders that may be triggered or exacerbated during heat waves, predisposing individuals to heat-related morbidity and mortality.

Design: Using health outcome data from Adelaide, South Australia, for 1993–2006, we estimated the effect of heat waves on hospital admissions and mortalities attributed to mental, behavioral, and cognitive disorders. We analyzed data using Poisson regression accounting for overdispersion and controlling for season and long-term trend, and we performed threshold analysis using hockey stick regression.

Results: Above a threshold of 26.7°C, we observed a positive association between ambient temperature and hospital admissions for mental and behavioral disorders. Compared with non–heat-wave periods, hospital admissions increased by 7.3% during heat waves. Specific illnesses for which admissions increased included organic illnesses, including symptomatic mental disorders ; dementia ; mood (affective) disorders ; neurotic, stress related, and somatoform disorders ; disorders of psychological development ; and senility. Mortalities attributed to mental and behavioral disorders increased during heat waves in the 65- to 74-year age group and in persons with schizophrenia, schizotypal, and delusional disorders. Dementia deaths increased in those up to 65 years of age.

Conclusion: Our results suggest that episodes of extreme heat pose a salient risk to the health and well-being of the mentally ill.

Relevance to Clinical or Professional Practice: Improvements in the management and care of the mentally ill need to be addressed to avoid an increase in psychiatric morbidity and mortality as heat waves become more frequent.

Key words: dementia, heat waves, mental health, psychiatric, schizophrenia, temperature, weather. Environ Health Perspect 116:1369–1375 (2008) .  doi:10.1289/ehp.11339 available via http://dx.doi.org/ [Online 30 June 2008]

Address correspondence to P. Bi, Discipline of Public Health, School of Population Health and Clinical Practice, Faculty of Health Sciences, Level 9, Tower Building, 10 Pulteney St., MPD 207, The University of Adelaide, South Australia, 5005 Australia. Telephone: 618-8303-3583. Fax: 618-8303-6885. E-mail: peng.bi@adelaide.edu.au

We thank the South Australian Department of Health and the Australian Bureau of Meteorology for their support and contribution of data. The work was funded by the Australian Research Council, Linkage Project LP0668223, via an Australian Postgraduate Award (Industry) .

The authors declare they have no competing financial interests.

Received 6 February 2008 ; accepted 25 June 2008.