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Self-reported data from the Australian Bureau of Statistics (ABS) 2014–15 National Health Survey (NHS) provides the opportunity to look at the prevalence of chronic disease comorbidity among the Australian population. Comorbidity data are presented for the following 8 chronic diseases:

  • arthritis
  • asthma
  • back problems
  • cancer
  • COPD (chronic obstructive pulmonary disease)
  • CVD (cardiovascular disease)
  • diabetes
  • mental health conditions.

These chronic diseases were selected for reporting because they are common, pose significant health problems, have been the focus of recent AIHW surveillance efforts, and action can be taken to prevent their occurrence. Chronic kidney disease is not included because of the identified low numbers using self-reported data. See data limitations below.

Describing comorbidity

Comorbidity refers to any two or more diseases that occur in one person at the same time. This may occur simply by chance; however, more often than not, diseases occur together because there are some associations between them. Diseases may share risk factors (for example smoking is a risk factor for many diseases), or one disease may be a risk factor in itself for another. For example, diabetes is a well-known risk factor for CVD, possibly due to diabetes increasing atherosclerosis (thickening of blood vessel walls with plaque deposits), which is the underlying cause of most CVD in Australia [1].

Ageing is a factor that has a particularly strong association with comorbidity. This is because older people are more vulnerable to the onset of many diseases, and an increased life expectancy in Australia, which means a greater opportunity for multiple conditions to arise [2].

The importance of reporting on comorbidity

Reporting on comorbidity is important to inform the planning for preventive, management and treatment services, and in the allocation of health care funding.

Comorbidities often indicate the presence of more severe disease. Therefore, comorbidity is associated with poorer prognosis, a greater frequency of visits to GPs and specialists, more hospital admissions and longer stays in hospital. Together these result in higher health care costs [1].

In addition, clinical treatment for people with comorbidities is more complex and time consuming than for people with a single condition. Multiple medications and therapies are often needed, which requires extra attention from clinicians to reduce the risk of treatment conflicts such as dangerous drug interactions [1].

Chronic disease combinations with high impact

Some combinations of comorbidity have particularly high impacts on the complexity of clinical management and health service use.

  • People hospitalised with both CVD and CKD record an average length of stay of 10.8 days, compared with 5.4 days for people hospitalised with CVD only and 4.9 days for people hospitalised with CKD only [3].
  • Detailed clinical guidelines advise clinicians on the treatment of asthma when co-existing with COPD, due to the impact of treatment on the individual conditions [4].
  • The presence of coronary heart disease in people with COPD requires more careful management of certain medications such as beta-blockers [5] [6].

Who experiences comorbidity?

According to the 2014–15 NHS, 1 in 4 (23%) Australians—5.3 million people—had two or more of the eight selected chronic diseases in 2014–15. The rate of comorbidity was higher for:

People aged 65 and over (60%) compared with people aged 0–44 (9.7%).

Females (25%) compared with males (21%).

People living in the lowest socioeconomic areas (30%) compared with the highest socioeconomic areas (19%).

People living in Regional and Remote areas (28%) compared with Major cities (21%).

The rate of comorbidity and the number of chronic diseases experienced (based on self-reported data) increases with age. Almost 1 in 3 (29%) people aged 65 and over reported having three or more chronic diseases, compared with just 2.4% of those under 45. 

Comorbidity of selected chronic diseases, by age, 2014–15

Stacked bar chart indicating the cormobidity of selected chronic diseases by age group in 2014-15. Most people aged 0-44 (around 60%) have no selected chronic diseases. Most people aged 45-64 (around 60%) have at least 1 chronic disease, and around 50% of those have two or more chronic diseases. 60% of people aged 65+ have 2 or more chronic diseases.

Note: The selected chronic diseases are: arthritis, asthma, back pain and problems, cancer, cardiovascular disease, chronic obstructive pulmonary disease, diabetes, and mental health conditions.

Sources: ABS 2015. National Health Survey: first results 2014–15. ABS cat. no. 4364.0.55.001. Canberra: ABS.

What are the most common chronic disease comorbidities?

The most common comorbidity combinations were:

  • arthritis with cardiovascular disease (7.4%)
  • arthritis with back pain and problems (5.1%)
  • back pain and problems with cardiovascular disease (5.0%).

Arthritis with cardiovascular disease was the most frequently occurring comorbidity combination in both males (6.3%) and females (8.5%), and reflected the pattern in the overall population.

Back pain featured in the second and third most common comorbidities among both males and females; among males it most frequently occurred with cardiovascular disease (5.1%) and mental health conditions (4.5%), and among females it featured with arthritis (5.8%) and mental health conditions (5.2%).

The top three chronic disease combinations for people aged 45 and over reflected the pattern in the overall population. Particularly for the 65-and-over age group, higher rates of comorbidities occured for:

  • arthritis occurring with cardiovascular disease (32%)
  • arthritis with back pain and problems (17%)
  • back pain and problems with cardiovascular disease (16%).

Among the 0–44 age group, combinations with mental health conditions were more common, co-occurring with back pain and problems for 3.3% and asthma for 2.7%. 

Most common comorbidities of selected chronic diseases, by age, 2014–15

Figure indicating the most common comorbidities of selected chronic diseases of different age groups, in 2014-15. The most common comorbidity for people aged 0-44 is back pain and problems with mental health conditions (3.3%). The most common for people aged 45-64 is arthritis and CVD (9.9%). The most common for people aged 65+ is arthritis and CVD (32%).

Source: ABS 2015. National Health Survey: first results 2014–15. ABS cat. no. 4364.0.55.001. Canberra: ABS.

Comorbidity among selected chronic diseases

Although cancer (1.6%), COPD (2.6%) and diabetes (5.1%) were the least reported of the eight selected chronic diseases in the 2014–15 NHS, people with these conditions were more likely than people with other conditions to have a comorbidity (90% of people with COPD, 85% of people with diabetes, and 82% of people with cancer had two or more chronic diseases). This is because people with COPD, diabetes or cancer tend to be older, and the likelihood of having multiple chronic diseases increases with age. 

Comorbidity of selected chronic diseases, by chronic disease, 2014–15

Column graph showing the comorbidity of selected chronic diseases by chronic disease in 2014-15. The chronic diseases with the greatest comorbidity are chronic obstructive pulmonary disease (around 90%), diabetes (around 80%) and cancer (around 80%).

COPD   chronic obstructive pulmonary disease.

Notes

  1. Y-axis % refers to the percentage of people with each chronic disease who had at least one other chronic disease (comorbidity).
  2. X-axis label % refers to the percentage of the population with each chronic disease (prevalence).

Source: ABS 2015. National Health Survey: first results 2014–15. ABS cat. no. 4364.0.55.001. Canberra: ABS.

Common comorbidities of the eight selected chronic diseases by broader body system groupings include:

Vascular diseases

742,000 people (3.2%) reported having both cardiovascular disease and diabetes.

Figure showing that 18% of people reported having cardiovascular disease, 5.1% reported having diabetes, and 3.2% reported having both.  

Musculoskeletal conditions

1.2 million people (5.1%) reported having both arthritis and back pain and problems.

Figure showing that 15% of people reported having arthritis, 16% reported having back pain and problems, and 5.1% reported having both.  

Chronic respiratory conditions

250,000 people (1.1%) reported having both asthma and COPD.

Figure showing that 11% of people reported having cardiovascular disease, 2.6% reported having chronic obstructive pulmonary disease, and 1.1% reported having both.  

Among people with any of the eight selected chronic diseases, the most commonly reported comorbid chronic diseases were cardiovascular disease, arthritis, back pain and problems, and mental health conditions. These four conditions featured prominently as comorbidities because they are strongly age related and the most commonly reported chronic diseases. For example:

Cardiovascular disease

Series of graphics indicating that cardiovascular disease was reported as a comorbidity among 63% of people with diabetes, 51% of people with cancer, and 49% of people with COPD.  

Arthritis

Series of graphics indicating that arthritis was reported as a comorbidity among 52% of people with COPD, 41% of people with diabetes, and 41% of people with cardiovascular disease.  

Back pain and problems

Series of graphics indicating that back pain and problems was reported as a comorbidity among 38% of people with COPD, 33% of people with arthritis, and 29% of people with diabetes.  

Mental health conditions

Series of graphics indicating that mental health conditions were reported as a comorbidity among 38% of people with COPD, 30% of people with back pain and problems, and 29% of people with asthma.  

Data limitations

When interpreting self-reported data, it is important to recognise that because we rely on respondents providing accurate information, the outputs may not be a true reflection of the situation. For example, self-reported data for chronic kidney disease substantially underestimate the prevalence when compared to biomedical testing: 1% according to self-reported data versus 10% according to measured results [1]. People also underestimate their weight yet overestimate their height, which are used to calculate body mass index for the assessment of overweight and obesity [7]. Measured data are, therefore, more reliable in such instances.

While the individual prevalence estimates for each disease are from the best available data sources, using the self-reported data from the ABS 2014–15 NHS enables us to look at the association between chronic diseases across the Australian population, which is not possible using separate data sources. More information about NHS and other data sources for monitoring are available at the AIHW website.

It is also important to note that information on comorbidities does not tell us about the impact of comorbidities, as this depends on the specific disease combinations and the severity of the individual diseases.


References

  1. Australian Institute of Health and Welfare (AIHW) 2014. Cardiovascular disease, diabetes and chronic kidney disease—Australian facts: prevalence and incidence. Cardiovascular, diabetes and chronic kidney disease series no. 2. Cat. no. CDK 2. Canberra: AIHW.
  2. AIHW: Tong, B and Stevenson C 2007. Comorbidity of cardiovascular disease, diabetes and chronic kidney disease in Australia. Cat. no. CVD 37. Canberra: AIHW.
  3. AIHW 2014. Cardiovascular disease, diabetes and chronic kidney disease—Australian facts: mortality. Cat. no. CDK 1. Canberra: AIHW.
  4. National Asthma Council Australia 2015. Managing coexisting asthma and COPD. Available from: https://www.asthmahandbook.org.au/clinical-issues/copd. Accessed 24 February 2015.
  5. Albouaini K et al. 2007. Beta-blockers use in patients with chronic obstructive pulmonary disease and concomitant cardiovascular conditions. International Journal of COPD 2(4):535–40.
  6. Du Q et al. 2014. Beta-blockers reduced the risk of mortality and exacerbation in patients with COPD: a meta-analysis of observational studies. PLoS One 9(11):e113048.
  7. ABS 2006. National Health Survey: Users' Guide - Electronic Publication, 2004–05. Cat. no. 4363.0.55.001. Canberra: AIHW.