Specialist Homelessness Services: feature analysis

Leading underlying causes of death are determined by grouping specific causes of death and counting the number of deaths assigned to each cause group. Over 14,000 specific causes of illness, injury and death are presented in the International Statistical Classification of Diseases and Related Health Problems, 10^th Revision (ICD-10). These causes can be grouped in a way that is meaningful for public health purposes.

A common grouping is by ICD chapters which are broad categories arranged according to the type of disease, the body system affected by the disease or the circumstances causing death. Each chapter is further divided into blocks of related diseases. Australian cause of death data by ICD-10 chapters and selected causes of death are published in the AIHW General Record of Incidence of Mortality (GRIM) books.

For leading underlying cause of death analysis, information needs to be more specific than ICD chapters and blocks. There is no standard method for grouping causes, however, the AIHW follows the recommendations of the World Health Organization (WHO) (Becker et al. 2006) with minor modifications to suit the Australian context. This grouping is a mix of ICD chapters, blocks and specific diseases to maximise information, separate out ill-defined causes and highlight health priority areas.

The leading underlying causes of death presented here are classified using an AIHW-modified version of A method for deriving leading causes of death (Becker et al. 2006).

Types of death

Causes of death are grouped to describe the type of death and whether it originated from a disease or condition, or from an injury, or whether the cause is unknown (ABS 2023). The AIHW uses the methodology described by the Australian Bureau of Statistics (ABS 2023) that groups types of death as:

• Natural Causes: deaths due to diseases (for example diabetes, cancer, heart disease etc.) (ICD codes A00-Q99, R00-R98).
• External Causes: deaths due to causes external to the body (for example intentional self-harm, transport accidents, falls, poisoning etc.) (ICD codes V01-Y98)
• Unknown Causes: deaths where it is unable to be determined whether the cause was natural or external(ICD code R99).

In the instance of an accidental or violent death, the underlying cause of death is classified according to the circumstances of the fatal injury, rather than the nature of the injury, which is coded separately. For example, a motorcyclist may crash into a tree (V27.4) and sustain multiple fractures to the skull and facial bones (S02.7), which leads to death. The underlying cause of death is the crash itself (V27.4), as it is the circumstance which led to the injuries that ultimately caused the death.

Multiple causes of death

Using a multiple cause approach to identify causes of death provides a more complete picture of the health status of Australians. However, these methods require a finely detailed cause list to identify, in addition to the underlying causes, conditions that commonly occur as consequences of the underlying cause (direct causes) or which are coexisting or contextual causes (contributory causes). Identifying the direct and contributory causes highlights a broader range of conditions which can be used to

• emphasise the involvement of potentially preventable complications of the underlying cause, such as sepsis, to inform strategies to minimise their occurrence.
• show the contribution of preventable causes and modifiable risk factor-related conditions, such as hypertension, to provide additional focus for prevention strategies.

It is important to note that the ‘Becker’ classification is specifically designed to identify the leading underlying causes of death (Becker et al. 2006). A more detailed grouping of conditions is required to identify common direct and contributory causes.

Some conditions, for example, sepsis, hypertension and pneumonitis, are not considered valid underlying causes of death. Theoretically, there is another (underlying) condition that led to sepsis or pneumonitis. Therefore, in assessing only the underlying cause, there is little need to draw out these sorts of conditions.

For assessment of the multiple causes, a detailed cause list was developed to facilitate identification of the common direct and contributory causes. Lower respiratory infections, pneumonitis and acute renal failure are common conditions that arise as consequences of disease and injuries, while hypertension (a preventable condition) and chronic kidney disease, commonly occur as significant contributors to death.

For example, influenza and lower respiratory infections were each extracted from the broader Becker grouping of Influenza and pneumonia to identify common direct causes. Similarly, acute renal failure and chronic kidney disease were extracted from the broader Becker grouping of diseases of the urinary system to identify these as direct and contributory causes, respectively.

Data for ICD-10 Z codes were excluded from the multiple cause of death analysis due to challenges around identifying coroner-referred deaths in the NACS dataset.

The complete cause list including cause group, cause name and International Classification of Disease (ICD-10) code inclusions for the multiple cause of death analysis are available Deaths in Australia technical notes.

Potentially avoidable deaths and potential years of life lost age inclusions

In this report, potentially avoidable deaths and years of potential life lost (PYLL) were calculated for individuals who died between the age of 1 and 74 years. This differs from reporting practices elsewhere, where deaths at age 0 may be included. This approach was adopted due to incomplete data on deaths at age 0 in the NACS dataset, as described in the Age at death section. Information on infant mortality in Australia is presented in the Australia’s mothers and babies report.