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CAUSE OF DEATH
In the age groups in which differences in death rates between Indigenous and non-Indigenous populations are greatest (35-54 years), ischaemic heart disease, diseases of the liver (i.e. alcoholic liver disease and cirrhosis of the liver), diabetes and other forms of heart disease are major causes of death (table 9.11). Indigenous males and females aged 35-54 years died from diabetes at 23 and 37 times the rates, and from influenza and pneumonia at 18 and 27 times the rates, of non-Indigenous males and females of the same age for these conditions. There were also large discrepancies between Indigenous and non-Indigenous mortality rates for assault (ratios of 16 and 12 for males and females respectively); chronic lower respiratory diseases (ratios of 14 and 12); mental and behavioural disorders due to psychoactive substance use (ratios of 12 and 19) and pedestrian injured in transport accident (ratios of 18 and 67). While some of these rates have been derived from a relatively small number of deaths - for example assault and pedestrian injured in transport accident among Indigenous women (17 and 23 deaths respectively) - differences between the two population groups are still striking.
Deaths higher than the expected number are referred to as 'excess deaths'. Excess deaths are calculated by subtracting the number of expected Indigenous deaths based on the age, sex and cause-specific rates of non-Indigenous Australians, from the number of actual deaths in the Indigenous population.
Over the period 2001-2005 there were 2,891 excess deaths among Indigenous males and 2,092 excess deaths among Indigenous females in Queensland, Western Australia, South Australia and the Northern Territory. Diseases of the circulatory system accounted for the highest proportion of excess deaths (2,006 deaths in total, 1,326 of which were excess deaths). Other major causes of excess deaths were external causes, endocrine, nutritional and metabolic diseases and diseases of the respiratory system. Deaths due to these causes were responsible for around two-thirds of excess deaths among Indigenous males and females (2,561 deaths in total, 1,921 of which were excess deaths) (table 9.12).
Diseases of the circulatory system
Diseases of the circulatory system were responsible for around 27% of total Indigenous male and female deaths for the period 2001-2005. In comparison, these diseases accounted for 34% of all male deaths and 40% of all female deaths for non-Indigenous Australians. Within circulatory system diseases, ischaemic heart diseases (heart attack, angina) were responsible for 64% of Indigenous male deaths and 49% of Indigenous female deaths, while cerebrovascular disease (stroke) accounted for 14% of male deaths and 19% of female deaths.
Compared with non-Indigenous Australians, Indigenous males and females experienced higher rates of mortality from diseases of the circulatory system in every age group. The greatest differences in age-specific death rates for males occurred in the age groups 25-34 and 35-44 years, with Indigenous males recording a rate 9 to 11 times the rate for non-Indigenous males (rates of around 69 and 251 per 100,000 for Indigenous males compared with 7 and 23 per 100,000 for non-Indigenous males). Indigenous females recorded rates of around 12 times the rates for non-Indigenous females for the 35-44 and 45-54 year age groups (rates of 32 and 122 per 100,000 for Indigenous females compared with 4 and 10 per 100,000 for non-Indigenous females) (graphs 9.13 and 9.14).
The major cause of Indigenous deaths within the endocrine disease category is diabetes. Diabetes has a far greater impact on mortality for the Indigenous population than for the non-Indigenous population. For the period 2001-2005, diabetes was responsible for 8% of total Indigenous deaths compared with 2% of non-Indigenous deaths. For non-Indigenous Australians, the proportion of total deaths caused by diabetes was 1% to 3% for all age groups from 25-34 years and over. For Indigenous Australians, diabetes was responsible for 10% of deaths in the 45-54 years age group and for 14% of total Indigenous deaths in the 55-64 year age group (graph 9.15).
9.15 DIABETES DEATHS(a) AS A PROPORTION OF TOTAL DEATHS(b)(c), by Indigenous status and age - 2001-2005
The earlier onset of diabetes experienced by the Indigenous population is reflected in the differences in age-specific death rates. For the period 2001-2005, Indigenous males in the 35-44 and 45-54 years age groups experienced age-specific death rates 16 and 31 times, respectively, the corresponding rates for non-Indigenous males (rates of 31 and 144 per 100,000 for Indigenous males compared with 2 and 5 per 100,000 for non-Indigenous males) (graph 9.16). For the same age groups, the rates experienced by Indigenous females were 32 and 46 times the corresponding non-Indigenous female rates (graph 9.17) (rates of 29 and 87 per 100,000 for Indigenous females compared with 1 and 2 per 100,000 for non-Indigenous females). The markedly higher death rates from diabetes in the Indigenous population are partly a reflection of the earlier onset of diabetes in this population compared with the non-Indigenous population combined with a high prevalence of some of the risk factors associated with diabetes such as smoking, hypertension and obesity. Higher death rates from diabetes may also reflect poorer management of diabetes among Indigenous people, in particular those living in rural and remote areas (Wood & Patterson 1999).
Chronic kidney disease
Chronic kidney disease includes diabetic nephropathy, hypertensive renal disease, glomerular disease and chronic renal failure and end-stage renal disease (ESRD). ESRD results when the kidneys cease functioning almost entirely, leading to a build up of waste products and excess water in the body causing progressively worse illness (AHMAC 2006). This is the last and most debilitating stage of chronic kidney disease in which dialysis or kidney transplantation is necessary to maintain life.
Chronic kidney disease was responsible for 2% and 5% of Indigenous male and female deaths respectively for the period 2001-2005. The overall death rates from chronic kidney disease were 7 and 9 times as high as the rates for non-Indigenous males and females respectively. Among Indigenous deaths from chronic kidney diseases, chronic renal failure accounted for 43% of male deaths and 37% of female deaths, while diabetic nephropathy accounted for 23% (males) and 25% (females) respectively.
Both Indigenous males and females experienced markedly higher rates of mortality from chronic kidney disease after the age of 25 years. The greatest differences in age-specific death rates for males occurred in the 45-54 year age group with Indigenous males recording a rate 31 times the rate for non-Indigenous males (50 compared with 2 deaths per 100,000) (graph 9.18). For females, the greatest difference in age-specific death rates also occurred in the 45-54 year age group with Indigenous females recording a rate 51 times that for non-Indigenous females (56 compared with 1 per 100,000) (graph 9.19).
External causes of mortality
The quality of external causes of death data is affected by differences in the way that coronial deaths are reported across the various jurisdictions and in procedures around reportable deaths (i.e. deaths reported to a coroner). In addition, statistics on suicide deaths are dependent on coronial processes to determine the intent of a death (whether intentional self-harm, accidental, homicide or undetermined intent) as this information is required for the correct ICD-10 coding of cause of death. The timing of data compilation can therefore be affected by the length of coronial processes. For more information on data quality issues pertaining to external causes of death data, see ABS Information Paper: External Causes of Death, Data Quality, 2005 (ABS 2007e).
For the period 2001-2005, deaths due to external causes, such as accidents, intentional self-harm (suicide) and assault accounted for 16% of all Indigenous deaths, compared with 6% of all deaths among non-Indigenous Australians. For both populations, males accounted for around 70% of the total deaths due to external causes. For Indigenous males, the leading causes of death from external causes were intentional self-harm (35%), transport accidents (27%) and assault (8%), while for Indigenous females the leading causes of death were transport accidents (30%), intentional self-harm (18%) and assault (16%).
Over the period 2001-2005, for most age groups the age-specific death rates for Indigenous males were two to three times the corresponding rates for non-Indigenous males (graph 9.20). Indigenous females experienced higher age-specific death rates than non-Indigenous females in every age group, with the greatest difference occurring in the 35-44 year age group. In this age group, Indigenous females recorded a rate almost five times that of non-Indigenous females (87 deaths per 100,000 compared with 18 per 100,000) (graph 9.21).
9.20 MALE DEATH RATES(a), EXTERNAL CAUSES OF MORBIDITY AND MORTALITY(b), by Indigenous status and age - 2001-2005
9.21 FEMALE DEATH RATES(a), EXTERNAL CAUSES OF MORBIDITY AND MORTALITY(b), by Indigenous status and age - 2001-2005
Intentional self-harm (suicide)
Intentional self-harm was the leading cause of death from external causes for Indigenous males for the 2001-2005 year period. The suicide rate was almost three times that for non-Indigenous males, with the major differences occurring in younger age groups. For Indigenous males aged 0-24 years and 25-34 years, the age-specific rates were three and four times the corresponding age-specific rates for non-Indigenous males respectively (graph 9.22).
The suicide rate for Indigenous females aged 0-24 years was five times the corresponding age-specific rates for non-Indigenous females. For age groups 45-54 years and over, age-specific rates for Indigenous females were similar to, or lower than the corresponding rates for non-Indigenous females (graph 9.23).
Assault is a significant cause of death for both Indigenous males and females. Over the period 2001-2005, the Indigenous male age-specific death rates for ten year age groups from 25 through to 54 were between 11 and 17 times the corresponding age-specific rate for non-Indigenous males, while for females the rates ranged between 9 and 23 times the equivalent age-specific rates for non-Indigenous females (graphs 9.24 and 9.25).
Neoplasms were responsible for 15% of total Indigenous deaths compared with 30% of total non-Indigenous deaths for the period 2001-2005. Nevertheless, Indigenous people are over-represented in deaths from cancer compared with non-Indigenous Australians (the SMR for males and females is 1.4 and 1.5 respectively). This apparent contradiction is due to high numbers of deaths for other causes in the Indigenous population as well as high mortality rates from neoplasms for Indigenous Australians in the middle age groups. The major causes of cancer deaths for Indigenous males were malignant neoplasms of the digestive organs (30% of total), malignant neoplasms of the respiratory and intrathoracic organs (30%), and malignant neoplasms of lip, oral cavity and pharynx (9%). For Indigenous females the major causes were malignant neoplasms of the respiratory and intrathoracic organs (21% of total), malignant neoplasms of the digestive organs (21%), and malignant neoplasms of the female genital organs (14%).
Indigenous people were over-represented in a number of cancer groups, including malignant neoplasms of the lip, oral cavity and pharynx (7% of total Indigenous cancer deaths compared with 2% of non-Indigenous cancer deaths), malignant neoplasms of the respiratory and intrathoracic organs (26% Indigenous, 20% non-Indigenous) and malignant neoplasms of the female genital organs, which includes cervical cancer (14% total Indigenous females, 9% non-Indigenous females). Most of these cancers are smoking-related which is a reflection of the higher prevalence of smoking among the Indigenous population. Cervical cancer is also preventable through Pap Smear screening.
Indigenous people were under-represented in other cancer groups, including melanoma and other malignant neoplasms of skin (1% of total Indigenous cancer deaths compared with 4% of non-Indigenous cancer deaths), and malignant neoplasms of male genital organs, which includes prostate cancer (4% of total Indigenous males, 13% of non-Indigenous males).
The 2001-2005 age-specific death rates for neoplasms indicate that for age groups 0-24 years and 65 years and over, the rates for Indigenous males and females were similar to those for non-Indigenous males and females. For the age groups 35-44, 45-54 and 55-64 years, the rates for Indigenous males and females were about twice the non-Indigenous rates (graphs 9.26 and 9.27).
Cancer mortality of the Northern Territory Indigenous population has been compared with that of the Australian population for 1977-2000 (Condon et al 2004). The cancer mortality rate among Indigenous people was higher than the total Australian rate for cancers of the liver, lungs, uterus, cervix and thyroid, and, in younger people only, for cancers of the oropharynx, oesophagus and pancreas. Northern Territory cancer mortality rates for Indigenous Australians were lower than the total Australian rates for renal cancers and melanoma, and, in older people only, for cancers of the prostate and bowel. Over the period 1977-2000, there were increases in death rates for cancers of the oropharynx, pancreas and lung; all three are smoking-related cancers.
A study by Condon et al (2005) compared people diagnosed with cancer in Western Australia and Tasmania with Indigenous people diagnosed with cancer in the Northern Territory over the period 1991-2001. The study found that Northern Territory Indigenous patients had poorer survival rates for most cancers and the relative risk of death was higher for cancers of the oropharynx, colon and rectum, pancreas, lung, uterus, cervix, vulva, lymphoma, breast and leukaemia. Survival rates are the proportion of all cancer patients alive at the beginning of the period who are still alive at the end of the period. It was concluded that for cancers of the liver, lung and oesophagus, higher Northern Territory Indigenous mortality rates were due mostly to higher cancer incidence rates. For other cancers that have better survival rates in all Australians, such as cancer of the thyroid and cervix, high Indigenous mortality rates were due to both higher incidence and lower survival.
Respiratory diseases, which include 'influenza' and 'pneumonia' and 'chronic lower respiratory diseases' (including asthma, bronchitis and emphysema), were responsible for 9% of total Indigenous deaths for the period 2001-2005. Like diabetes, respiratory diseases affect the Indigenous population at younger age groups than is the case for the non-Indigenous population, and this is reflected in the differences in age-specific death rates from these diseases. For the period 2001-2005, Indigenous males in the 35-44 years age group experienced age-specific death rates 22 times higher than the corresponding rate for non-Indigenous males (63 per 100,000 compared with 3 per 100,000), while the rate for Indigenous females in this age group was 20 times higher than that for the corresponding rate for non-Indigenous females (37 per 100,000 compared with 2 per 100,000) (graphs 9.28 and 9.29).
Multiple causes of death
Multiple causes of death include all causes and conditions reported on the death certificate. Since 1997, the ABS has coded all causes of death reported on each death certificate, including the underlying, immediate and other associated causes of death. While only one cause can be recorded as the underlying cause of death, many deaths due to chronic diseases, such as heart disease, kidney disease and diabetes often occur with concurrent or co-existing conditions. It is useful, therefore, to describe the extent to which any or all of these conditions have been reported. For deaths where the underlying cause was identified as an external cause, multiple causes include circumstances of injury, the nature of injury as well as any other conditions reported on the death certificate.
For the 7,544 Indigenous deaths in 2001-2005 in Queensland, Western Australia, South Australia and the Northern Territory, there was a total of 23,977 causes reported, an average of three causes per death. Deaths where only a single cause was reported occurred in 15% of total Indigenous male deaths and 12% of total Indigenous female deaths, less than for non-Indigenous males (22%) and females (24%) (table 9.30). Correspondingly, deaths where multiple causes were reported were more common among Indigenous people. For example, 27% of deaths among Indigenous males and 29% of deaths among Indigenous females recorded five or more causes of death, compared with 15% of non-Indigenous male and female deaths.
Table 9.31 shows the relationships between a number of underlying causes of death and associated causes for Indigenous and non-Indigenous Australians. For deaths from ischaemic heart disease, diabetes was reported as an associated cause of death among Indigenous males and females at two to three times the rates of non-Indigenous males and females. For deaths from diabetes, renal failure was reported as an associated cause of death among Indigenous males and females at almost twice the rates of non-Indigenous males and females.
Table 9.32 uses the recording of multiple causes of death to associate the category of external cause of death with the nature of the injury sustained by Indigenous people. For the period 2001-2005, of all deaths from transport accidents, 42% involved injuries to multiple body parts, 38% involved injuries to the head and 17% involved injuries to the chest. For deaths from accidents other than transport accidents, 33% were for 'other and unspecified effect', while injuries to the head involved 15% of deaths and poisoning involved 13% of deaths from these accidents. Most deaths from intentional self-harm were for 'other and unspecified effects' (which includes suffocation and drowning) (85%), while deaths from assault most commonly involved injuries to the head (27%) or to the chest (32%).