Multiple causes of death in Australia: an analysis of all natural and selected chronic disease causes of death 1997-2007

Patterns of cause of death are usually compiled using only one of the conditions reported on the death certificate—the underlying cause (that is, the disease or injury that initiated the train of events leading directly to death, or the circumstances of the accident or violence that produced the fatal injury). Analysis of the underlying cause of death is important as it is a point at which preventive interventions can be targeted (WHO 2009). However, in the majority of deaths, more than one disease is indicated as causing or significantly contributing to the death. Information about all the diseases that play a role in causing a death is referred to as multiple causes of death.

The use of multiple causes of death data to describe patterns of mortality is becoming more prominent (for examples, see ABS 2012; Desequelles et al. 2010, Gorina & Lentzner 2008; Redelings et al. 2006; Redelings et al. 2007). These data provide a more complete picture of all the conditions that contribute to deaths. These data can also expand the knowledge base for guiding health policy and funding activities, enhance other measures of population health that rely on cause of death data, such as burden of disease, and improve the comparability of data for international comparisons of mortality. Furthermore, descriptions of the diseases that commonly contribute to death and their association with specific other diseases can improve understanding of the joint role of diseases on death and provide insight for developing alternative interventions to enhance quality of life.

Chronic diseases are a major cause of morbidity and mortality in Australia and the prevalence of many chronic diseases is increasing (AIHW 2012). The nature of the leading causes of death has changed during the past century from infectious diseases to chronic diseases. People are also living longer and ageing of the population is associated with increasing co-morbidities, particularly when chronic diseases are present.

Assessments of all diseases that contribute to death are particularly relevant to chronic diseases deaths. This bulletin is the first comprehensive application of multiple causes of death statistics, including trends over time, to natural causes of death and chronic diseases of public health importance.

Both age and the condition selected as the underlying cause of death typically influence the number and types of multiple causes (Desequelles et al. 2010; Gorina & Lentzner 2008; Wilkins et al. 1997). In this bulletin these aspects of multiple causes of death are explored for broad categories of disease and for selected chronic disease causes of death (see Appendix for a list of the disease categories used in this bulletin).

Many deaths due to the chronic diseases reported in this bulletin are preventable and many of the deaths occur among people aged less than 75. In addition, chronic diseases often co-exist with other diseases and the likelihood of having one or more chronic diseases increases with age (AIHW 2012). Consequently, an assessment of the mortality caused by and associated with these chronic diseases is warranted.

The information gained through analysis of multiple causes of death data can facilitate an understanding of the common patterns of diseases that contribute to chronic diseases deaths, while also providing a basis for surveillance of emerging patterns over time.

An assessment of the variation in multiple causes of death by age, and by other sociodemographic characteristics, such as Indigenous status and remoteness and socioeconomic status, is also presented.

What are multiple causes of death?

Multiple causes of death occur when two or more diseases or conditions are recorded as contributing to death. A Medical Certificate of Cause of Death (death certificate) is used for documenting the diseases considered to be instrumental in causing a death. Usually a medical practitioner documents the diseases that caused the death on the death certificate, but for some deaths (in Australia) a coroner provides information about the causes.

The World Health Organization (WHO) recommends a standard format for death certificates that can be used for collating international statistics on causes of death (WHO 2009). The WHO recommendations for documenting the causes of death have been adopted throughout Australia.

The format of the death certificate enables a medical practitioner to document all medical conditions instrumental in causing the death, including the condition that led directly to death (the immediate cause), all the antecedent causes (that is, those that occurred as a result of the reported underlying cause and before the immediate cause) and all other significant conditions that contributed to the death but were not related to the disease or condition that caused it. The terminology to describe the different cause types used in this bulletin is presented in Box 1.

Multiple cause of death data represent all the diseases or conditions reported on a death certificate. The Australian Bureaus of Statistics (ABS) defines multiple cause coding as 'the coding of all morbid conditions, diseases and injuries entered on the death certificate, including those involved in the morbid train of events leading to the deaths which were classified as either the underlying cause, the immediate cause, or any intervening causes, and those conditions which contributed to death but were not related to the disease or condition causing death' (ABS 2012).

The information documented on death certificates is coded by the ABS to the international standard recommended by the WHO. The death certificate indicates each cause type (underlying, antecedent and other significant contributory causes) that should be documented. The coding process considers the sequence of occurrence of each disease or health condition, removes duplicate disease information and applies other logical rules to select the underlying and associated causes. This process is automated and results in a standardised output that can be used for statistical analyses of causes of death, at both a national and international level.

What are the benefits of using multiple causes of death data?

Analyses using multiple causes of death data provide a more complete representation of all diseases and conditions that caused the death. Numerous authors have described the benefits of using multiple causes of death data; some recent accounts include ABS 2012; Desequelles et al. 2010; Gorina & Lentzner 2008; Redelings et al. 2006; Redelings et al. 2007. Some of the advantages of these data are:

• Deaths infrequently have a single cause. Therefore in describing patterns of mortality using only the underlying cause, important cause information is overlooked. The death certification process (in Australia) allows for up to 20 diseases to be reported as causing or contributing to a death. Analyses of multiple causes of death data complement routine analyses based on only the underlying cause and offer broader insight into the disease processes occurring at the end of life.
• In certifying the cause of death only one disease should be indicated as the underlying cause. In deaths involving multiple chronic diseases that are each potentially fatal, the decision about which disease to certify as the underlying cause can be arbitrary (Gorina & Lentzner 2008). Certification practices vary between practitioners and jurisdictions, which can also lead to inconsistency in the documentation of the underlying cause (Smith Sedhev & Hutchins 2001). Given the nature of chronic diseases, the tendency for these to occur jointly with other chronic diseases, and the complexity of selecting the underlying cause among the presence of multiple chronic diseases, analyses based on all the conditions influencing the death are highly applicable to chronic disease deaths.
• Multiple causes of death data facilitate understanding of the complexity of the morbid processes and the connection between diseases as they occur at the time of death. For example, an assessment of the joint role of diseases in contributing to death enables an understanding of the impact of specific co-morbidities at the time of death. These kinds of analyses can provide insight into other target points to, where possible, prevent death (Redelings et al. 2006) or enhance quality of life, and provide better information to contribute to debate around end of life care.
• Multiple causes of death data can improve the comparability of causes of death data presented in an international context. While many countries use an automated coding system to produce deaths statistics, there can be differences in certification practices (that is, in completing the death certificate). For example, countries may differ in the way that medical practitioners are trained to certify deaths, or some countries may have policies that influence certification practices. These differences can influence variation in statistics based on the underlying cause only, while estimates based on multiple causes of death data capture all mentions of the diseases involved in causing death and may be more comparable where certification practices differ.
• Levels of mortality in a population, for specific causes of death and among specific age groups, are a fundamental measure of public health and can be used to guide heath policy. However, routine reporting of information about the causes of death is usually based on the underlying cause only and the contribution of other important diseases is overlooked. Patterns of mortality derived from multiple cause data provide a more complete assessment of the contribution of all diseases to mortality in a population. This improves the information base for guiding health policy and funding activities as well as enhancing population health analyses that rely on cause of death information such as estimates of burden of disease.

Objectives of this bulletin

The objectives of this bulletin are to:

• describe and quantify the information that is overlooked in using only the underlying cause of death to describe patterns of mortality in the population
• provide a more complete description of chronic disease deaths by considering the contribution of multiple conditions to mortality
• explore patterns of diseases that are commonly associated with deaths due to selected chronic diseases.

Scope of this bulletin

In this bulletin, multiple causes of death data are used to describe patterns of mortality by considering all diseases recorded as contributing to deaths. Only deaths where the underlying cause was coded to a natural cause are included; that is, deaths due to external and ill-defined causes are excluded. The results describe the number of conditions typically contributing to deaths and the variation over time and between different age groups.

Patterns of multiple causes of death are assessed to determine any differences between different population groups, specifically between Indigenous and non-Indigenous Australians, and people living in different areas of remoteness and different areas of socioeconomic status.

The analyses in this bulletin provide complementary information about deaths due to leading chronic disease conditions as described in the Key indicators of progress for chronic disease and associated determinants: technical report (AIHW 2009); see the Appendix for the list of these chronic diseases.

Assessment of the strength of association between diseases that jointly contribute to death is important and useful for improving the knowledge of contributory causes of death. It can provide a useful foundation for understanding alternative health interventions. However, this assessment was out of scope for this bulletin.