Australian Burden of Disease Study: Methods and supplementary material 2018

Deaths related to blood & metabolic disorders were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). Deaths coded to E85.3, E85.4, E85.8, E85.9, were proportionally redistributed to all diseases excluding injuries, reproductive & maternal conditions, oral disorders and hearing & vision disorders. Deaths coded to E86 and E87 were proportionally redistributed across all disease groups (excluding reproductive & maternal conditions, oral disorders and hearing & vision disorders) (Table 3.1).

Cancer-related deaths were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list).

Deaths coded to intestinal tract, part unspecified (C26.0) were assigned to bowel cancer, instead of being redistributed as part of the ABDS algorithm for ill-defined digestive cancers. This aligns with the AIHW cancer mortality reporting and the ABS reporting practice.

Updated algorithms were used for cancer of other and ill-defined digestive organs (C26–excluding C26.0) and cancers of ill-defined, secondary unknown primary sites (C76–C80). Their redistributed were based on direct evidence from the Western Australian cancer registry (see redistribution tables below).

Although also a candidate for redistribution, there were insufficient deaths due to other and ill‑defined respiratory organs (C39) in the Western Australian cancer registry to develop a redistribution algorithm. Deaths coded to C39 were instead assigned to ‘cancer of unknown primary site’.

Similarly, cancers of multiple independent primary sites (C97) could not be redistributed using direct evidence, as a specific cancer cannot be assigned to these by cancer registries. Consequently, deaths coded to C97 were also assigned directly to ‘cancer of unknown primary site’.

The same direct evidence algorithms were applied to all three reference periods.

Table 4.1: Redistribution proportions of other and ill-defined digestive organs (C26–excluding C26.0), by age (years) and sex

 Source: Western Australia Cancer Registry data, 2013–2017; AIHW National Mortality Database.

Table 4.2: Redistribution proportions of ill-defined cancers (C39, C76–C80, C97), by age (years) and sex

 Source: Western Australia Cancer Registry data, 2013–2017; AIHW National Mortality Database.

Cardiovascular disease-related deaths were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). Deaths coded to hypertension (I10, I13, I15) and heart failure (I50) were redistributed using the indirect MCOD method to all diseases excluding injuries, reproductive & maternal conditions, oral disorders and hearing & vision disorders, and to selected cardiovascular and infant & congenital conditions, respectively. Deaths coded to cardiac arrest and cardiac conduction disorders were proportionally distributed across all diseases (except reproductive & maternal conditions, oral disorders and hearing & vision disorders), while deaths coded to unspecified atherosclerosis and cardiac signs and symptoms were proportionally distributed across all disease groups excluding cancer, injuries, infectious diseases, reproductive & maternal conditions, oral disorders and hearing & vision disorders.

Endocrine disorder deaths were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). Deaths coded to gestational diabetes (O24.4) were assigned to reproductive & maternal conditions. Deaths due to diabetic nephropathy (E10.2, E11.2, E13.2, E14.2) were assigned to kidney and urinary diseases. Deaths due to unspecified diabetes were redistributed across type 1, type 2 and other diabetes.

Deaths related to gastrointestinal disorders were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). Deaths coded to unspecified digestive diseases (K92) were redistributed using the direct evidence and indirect MCOD method to chronic liver disease, gastroduodenal disorders and diverticulitis. Deaths coded to peritonitis (K65–K66) were also redistributed using direct evidence and indirect MCOD to gastroduodenal disorders, hernias, pancreatitis, gallbladder and bile duct disease, paralytic ileus & intestinal obstruction without hernia and inflammatory bowel disease. Toxic liver disease with acute hepatitis was redistributed proportionally to all causes (except reproductive & maternal conditions, oral disorders and hearing & vision disorders).

Deaths from hearing & vision disorders were treated as implausible causes of death. Deaths in the NMD related to hearing & vision disorders were redistributed proportionally across all diseases, excluding reproductive & maternal conditions and oral disorders.

Deaths related to infant & congenital conditions were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). Deaths due to congenital malformations with ICD-10 codes Q10–Q18, Q38.1, Q54, Q65–Q74, Q82–Q84, Q89.9, Q99.9 were considered implausible causes of death, and were redistributed proportionally to all non-communicable diseases (that is, excluding infections, cancer and injuries) excluding reproductive & maternal conditions, oral disorders and hearing & vision disorders.

Deaths from infectious diseases were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). A small number of ICD–10 codes relating to infectious diseases were assigned to other disease groups as follows: some infections of the skin and subcutaneous tissue were allocated to skin conditions, infections of the amniotic sac and membranes were allocated to reproductive & maternal conditions, and some neonatal infections were allocated to infant & congenital conditions (see Table 3.1).

Septicaemia (A40, excluding A40.3, and A41) was the largest cause of death requiring redistribution within the infections group. While septicaemia is a clearly defined clinical entity, other underlying causes would have led to the chain of events culminating in the death (Naghavi et al. 2010). Deaths coded to septicaemia were redistributed using the indirect MCOD method.

Changes to selection rules for coding causes of death in recent years have allowed more chronic conditions, such as cancers, coded to Part 2 of the death certificate (associated causes), to be selected as the underlying cause of death when septicaemia appears in Part 1 (underlying cause) of the death certificate. Following discussion with mortality data experts, deaths recorded with septicaemia as the underlying cause were not redistributed to selected chronic conditions, but instead to more acute conditions, such as urinary tract infections.

References

Naghavi M, Makela S, Foreman K, O’Brien J, Pourmalek F & Lozano R 2010. Algorithms for enhancing public health utility of national causes-of-death data. Population Health Metrics 20108:9.

Injury deaths were identified from the NMD as deaths with an underlying cause coded to an external cause of injury from ICD-10 ‘Chapter XX: External causes of morbidity and mortality’ in the range V01–Y98 (see Mapping of ICD-10 codes to the disease list).

Redistribution

Some external causes of injury were identified for redistribution, specifically:

• Y10–Y34 (event of undetermined intent)—redistributed across injury causes based on direct evidence informed by the ABS revisions process

• X59 (exposure to unspecified factor)—redistributed across injury causes using proportional allocation

• Y87.2 (non-specific injury deaths)—(sequelae of events of undetermined intent), Y89.9 (sequelae of unspecified external cause), Y90–Y98 (supplementary factors related to causes of morbidity and mortality classified elsewhere)—redistributed across all causes using proportional allocation. 

• Redistribution of ICD-10 code X59 Exposure to unspecified factor. Previously these were redistributed proportionately across injuries. Using similar methods to AIHW injury reports, we used associated causes of death (fracture codes) to identify additional deaths from falls (2,766 deaths), thereby resulting in less X59 deaths being needed to be redistributed (727 deaths).

  • Additional fall deaths were identified as those having X59 as the UCOD with a fracture code in the ACOD:
  • the UCOD was an Unintentional fall (W00–W19); or
  • the UCOD was coded as Exposure to unspecified factor (X59) and the MCODs included a code for Fracture (the codes for fractures are S02, S12, S22, S32, S42, S52, S62, S72, S82, S92, T02, T08, T10, T12 and T14.2).

Injury deaths may also arise from other redistribution causes having injuries as the target cause for redistribution. Some examples are septicaemia, pneumonitis, unknown causes and all other non-specific, intermediate and immediate causes. The redistribution groups, methods and target causes are described in Table 3.1.

Table 4.3: Priority of nature of injury categories for assigning a single injury cause of death for deaths with an external cause of injury as the underlying cause

Notes

1. Soft tissue injuries and dislocations are excluded as injuries that lead to death.
2. Tibia and ankle fractures and humerus fractures are grouped with ‘Other fractures’ for this purpose.

Conversion to nature of injury

YLL were also estimated for the other injury perspective—nature of injury using codes from ICD-10 ‘Chapter XIX: Injury poisoning and certain other consequences of external causes’ in the range S00–T75, T79–T81 and T88. The external cause of injury was mapped to the nature of injury using information reported in the associated causes of death.

Each death can have more than one associated cause of death (which are not reported in order of severity). Hence, the single most relevant associated cause of death must be identified. We used a hierarchical approach to identify, from each death, the injury most likely to have caused the death (Table 4.3). The hierarchy used in the ABDS is a modified version of that used in the NZBDS (NZMOH, unpublished). In the NZBDS, the likelihood that the injury caused death was based on the nature of the injury, prognosis and clinical knowledge of injury conditions.

For example, if an injury death reports traumatic brain injury (TBI) as an associated cause of death, this will be selected as the injury most likely to have caused the death and is thus ascribed as the nature of injury. Where TBI is not reported as an associated cause, the next injury most likely to have resulted in death is selected as the nature of injury.

The relationship between external cause and nature of injury was used to develop age- and sex-specific matrices (cross-tabulations) for mapping YLL by external cause to YLL by nature of injury, maintaining internal consistency for YLL.

Nature of injury category was found for more than 96% of injury death records. Only records with an external cause of death code and a nature of injury code were used to develop the mapping algorithm.

The matrices were applied to all deaths by external cause following redistribution. 

Table 4.4: List of injury categories used in the ABDS 2018 for nature of injury and external cause of injury

Deaths related to kidney & urinary diseases were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). Please note that the ICD-10 codes used to align deaths to chronic kidney disease in the ABDS 2018 are different to the ICD-10 codes used for routine reporting of deaths due to chronic kidney disease in the AIHW. For more information on those ICD-10 codes, see Appendix B of Indicators of socioeconomic inequalities in cardiovascular disease, diabetes and chronic kidney disease (AIHW 2019).

For the kidney & urinary disease group, the relevant ICD-10 codes that need to be redistributed are N17 (acute renal failure) and N19 (unspecified renal failure). Acute kidney failure (N17) was redistributed because it has multiple causes and is generally a consequence of many other diseases—for example, injury, infection, cancer and myocardial infarction. Unspecified renal failure (N19) was redistributed to chronic or acute renal failure.

These codes were redistributed using a 2-step approach. In the first step, deaths due to N19 (unspecified renal failure) were redistributed using direct evidence from information on hospitalisations prior to death in linked data from New South Wales and Western Australia (AIHW 2014). N19 deaths were then redistributed to N17 (acute renal failure) and N18 (chronic renal failure) according to the proportions obtained from the linked data. 

In the second step, N17 deaths (including those reassigned from N19) were then redistributed over all disease groups, using the indirect MCOD method.

References

AIHW 2014. Assessment of the coding of ESKD in deaths and hospitalisation data: a working paper. Cat. no. PHE 182. Canberra: AIHW.

AIHW 2019. Indicators of socioeconomic inequalities in cardiovascular disease, diabetes and chronic kidney disease. Cat. no. CDK 12. Canberra: AIHW.

Deaths related to mental & substance use were assigned from the NMD, as defined by the disease list (Mapping of ICD-10 codes to the disease list). Deaths due to mental disorder, unspecified (F99) were proportionally redistributed to all diseases (except reproductive & maternal conditions, oral disorders and hearing & vision disorders).

Codes for accidental poisoning by, and exposure to, drugs/alcohol (X41, X42, X45) were not included in estimates of fatal burden for substance use disorders. Instead, these deaths are included in estimates for poisoning under the injury disease group. This approach is consistent with the determinations made by coroners for such deaths in Australia.

As part of the ABS revisions process for mortality data, deaths that are confirmed as being accidental are coded under injuries. Deaths that are initially coded as poisoning with ‘undetermined intent’, and are determined by the coroner to be due to a drug dependence, were recoded under alcohol or substance use disorders. As such, these deaths were included in estimates of fatal burden for substance use disorders in the ABDS.

Deaths related to musculoskeletal conditions were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). No musculoskeletal condition deaths were redistributed.

Neurological conditions-related deaths were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). Deaths coded to ICD-10 codes G81–G83 were proportionally distributed across all diseases using proportions derived from Australian all‑cause mortality data.

Oral disorder deaths were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). No deaths due to oral disorders were redistributed. Oral disorders were also not a target cause for redistribution.

Deaths related to reproductive & maternal conditions were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). Deaths coded to N60, N61, N84–N90 and O94 were redistributed proportionately to all disease excluding reproductive & maternal conditions, oral disorders and hearing & vision disorders.

Reproductive & maternal conditions were not a target cause for redistribution.

Deaths due to respiratory diseases were assigned from the NMD as defined by the disease list and were based on the ICD-10 codes shown in Mapping of ICD-10 codes to the disease list. Deaths due to respiratory failure (J96) were redistributed across all diseases (excluding reproductive & maternal conditions, oral disorders and hearing & vision disorders) using proportional allocation. Symptoms and signs involving the respiratory system (R04–R07) were redistributed across all diseases (excluding injuries, reproductive & maternal conditions, oral disorders and hearing & vision disorders) using proportional allocation. Pneumonitis deaths (J69) were redistributed using the indirect MCOD method with all diseases (excluding reproductive & maternal conditions, oral disorders and hearing & vision disorders) in the target range.

Deaths related to skin disorders were assigned from the NMD as defined by the disease list (Mapping of ICD-10 codes to the disease list). Deaths coded to L04, L21–L25, L27–L30, L41–L45, L52–L53, L55‍–‍L60, L63–L68, L71–L85, L87, L90–L92, L94, L98.0, L98.1, L98.8 and L98.9 were redistributed proportionally to all diseases (excluding reproductive & maternal conditions, oral disorders and hearing & vision disorders) (see Table 3.1).