Incidence and prevalence of chronic diseases 

Chronic diseases are highly prevalent in Australia, reflecting the long-term nature of most of these conditions. In 2004-05, 77% of respondents in the National Health Survey said they had one or more long-term health conditions (one that has lasted or is expected to last for 6 months or more). Among those aged 15 and over, this prevalence was 86%. The corresponding levels in 2001 were 78% and 87% and in 1995 were 76% and 83%.

Precise measures of incidence (the number of new cases within a given period) and prevalence (the number of existing cases at a given period) are often difficult to obtain. Incidence estimates are available for those diseases for which there are registers, while prevalence estimates are usually based on national surveys. This section therefore draws on a variety of sources to provide a picture of the impact of these diseases and conditions. 

• Coronary heart disease (CHD)
• Stroke
• Lung cancer
• Colorectal cancer
• Depression
• Diabetes
• Asthma
• Chronic obstructive pulmonary disease
• Chronic kidney disease
• Oral diseases
• Arthritis
• Osteoporosis.

Coronary heart disease (CHD)

Based on self-reported data from the 2004-05 National Health Survey, 1.4% of those surveyed reported having symptoms of CHD. This corresponds to around 280,223 Australians affected. Around three-quarters of people with CHD reported having angina, and around one-third reported having had a heart attack.

Nearly twice as many males as females are affected by CHD. CHD rates increase rapidly with age for both males and females, with almost two-thirds of people with CHD aged 65 and over in 2004-05 (Figure 1).

Figure 1: Age-specific prevalence of coronary heart disease, Australia, 2004-05

Source: AIHW analysis of the 2004-05 ABS National Health Survey.

The estimation of CHD incidence is done indirectly. In 2001-02, there were an estimated 48,700 CHD events (sum of non-fatal hospitalisations for acute myocardial infarction and the number of CHD deaths in the population) among 40-90 year old Australians (29,800 among men and 18,900 among women). Around one-half of these events were fatal (case fatality of 46% or 22,400 cases).

The incidence of coronary heart disease increases dramatically with age -  rates among 75-90 year olds were 18 times those of 40-54 year olds.

The age-standardised incidence of CHD has declined over the last decade, falling by around one-quarter between 1993-94 and 2001-02.

This information on CHD incidence has been taken from the AIHW publication Heart, stroke and vascular diseases - Australian facts 2004, pages 27-28. For more information, see the AIHW website Cardiovascular Health. 

Stroke

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Based on self-reported data from the 2003 Survey of Disability, Ageing and Carers, an estimated 346,700 Australians have had a stroke sometime in their lives. More males than females had experienced a stroke (178,334 versus 168,334) and males were more likely to have a stroke at a younger age (60-74) than females (Figure 2).

Figure 2: Number of persons experiencing stroke, Australia, 2004-05

Source: AIHW: Senes 2006. How we manage stroke in Australia. Cat. No. CVD 31. Canberra: AIHW.

There are no national data on the incidence (new cases) of stroke. Estimates have, however, been made based on rates obtained from local registers in Melbourne and Perth. It is estimated that each year there are about 40,000-48,000 stroke events among Australians, which equates to a stroke occurring every 11-13 minutes. The majority (around 70%) of these are first-ever strokes. Also, about 12,000 people who have previously had a stroke suffer another stroke every year. 

For more information, see the AIHW publications Heart, stroke and vascular diseases - Australian facts 2004 or How we manage stroke in Australia, or visit the AIHW Cardiovascular Health website.

Lung cancer

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According to the National Cancer Statistics Clearing House, lung cancer is the fourth most commonly diagnosed cancer in Australia. There were 8,249 new cases in 2003, with an incidence rate of 40.4 per 100,000 population. New cases of lung cancer currently occur in males at more than twice the rate among females: 57.1 per 100,000 (age-standardised) compared to 27.1 per 100,000. 

Lung cancer incidence increases with age (Figure 3), with the highest incidence in males aged 80-84 (471 per 100,000) and females aged 75-79 (199 per 100,000) in 2003. 

Figure 3: Age-specific incidence rates for lung cancer, Australia, 2003

Source: Australian Institute of Health and Welfare (AIHW) and Australian Association of Cancer Registries (AACR) 2004. Cancer in Australia 2001. AIHW cat. no. CAN 23. Canberra: AIHW.

Between 1990 and 2003, the incidence of lung cancer among males fell by an average of 2.4% per year. In contrast, incidence among females increased by 1.0% annually. 

Data on the prevalence of lung cancer are difficult to obtain, as the number is probably too small to be measured in the NHS. However, given the short survival time after diagnosis, the number of prevalent cases of lung cancer would not be much greater than the number of new cases (see the AIHW publication Cancer Survival in Australia, 2001 Part 1: National Summary Statistics for detailed lung cancer survival information). 

Lung cancer incidence data are available on the Interactive cancer data page of the AIHW website.

Colorectal cancer 

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The colorectal cancer is the second most frequently occurring cancer in Australian men (behind prostate cancer) and women (behind breast cancer) if skin cancers other than melanoma are excluded. If non-melanocytic skin cancer is excluded,  it is the most frequently diagnosed cancer in Australia.

In 2003, there were 12,536 new cases (13.5% of all new cases diagnosed), an incidence rate of 61.3 per 100,000 population. Males have a much higher incidence (73.2 per 100,000) compared to the female rate (51.1 per 100,000). 

The risk of colorectal cancer increases with age (Figure 4), especially after the age of 45. In 2003, the highest incidence rates were found in males (477 per 100,000) and females (370 per 100,000) aged 80 to 84 years.

Figure 4: Age-sex specific incidence rates for colorectal cancer, Australia, 2003

Source: Australian Institute of Health and Welfare (AIHW) and Australian Association of Cancer Registries (AACR) 2007. Cancer in Australia, an overview, 2006. AIHW cat. no. CAN 32. Canberra: AIHW.

From 1991 to 2003, incidence rates for colorectal cancer have mixed trend of increase and decrease and are currently decreasing slowly, by 0.3% per year for both males and females. 

There are no national data on the prevalence of colorectal cancer. The incidence data on colorectal cancer are available on the Interactive cancer data page of the AIHW website.

Depression

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Depression is part of a group of mental and behavioural problems called 'affective' or mood disorders. In the 2004-05 ABS National Health Survey, nearly 1,052,600 Australians reported they had such a problem. However, the ABS did not publish the number of people specifically reporting they had been diagnosed with depression. 

An earlier ABS survey, the 1997 National Survey of Mental Health and Wellbeing, used internationally recognised diagnostic interview schedules to assess the prevalence of mental disorder through the measurement of symptoms. This survey found that about 700,000 Australian adults aged 18 years and over, 6% of the population, had experienced depression during the 12 months prior to the survey. Depression was more prevalent among females with a rate of 8.7%, compared to 5.2% among males (Figure 5). Depression was present in about 3% of children (aged 6-12 years) and 5% of adolescents (aged 13-17 years). 

Figure 5: Age-specific prevalence of depression, 1997

Sources: ABS 1998. Mental health and wellbeing: profile of adults, Australia, 1997. ABS Cat. No. 4326.0. Canberra: ABS; Sawyer M, Arney F, Baghurst P et al 2000. The mental health of young people in Australia. Canberra: Mental Health and Special Program Branch, DHAC.

Diabetes

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In the 2004-05 ABS National Health Survey, nearly 700,000 Australians reported that they had diabetes. Of these, 580,000 said they had Type 2 diabetes. However, it is recognised that many more people have undiagnosed diabetes, in part because the symptoms of the disease are not apparent in its early stages.  

The prevalence of Type 2 diabetes rises with age (Figure 6). The highest prevalence rates were among males aged 65-74 and 75 and over.

Figure 6: Age-specific prevalence rates of Type 2 diabetes among Australians aged 25+, 2004-05

Source: AIHW analysis of the 2004-05 ABS National Health Survey.

A more accurate estimate of the prevalence of diabetes requires a biomedical survey using blood samples. The only recent national survey of this type was the 1999-2000 Australian Diabetes, Obesity and Lifestyle (AusDiab) Study, which found that about 850,000 Australians aged 25 and over had Type 2 diabetes, representing 7.2% of that population (7.6% of males and 6.7% of females).  

Asthma

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In the 2004-05 ABS National Health Survey, approximately 2 million (10.2%) Australians reported asthma as a current or long-term condition (9.0% of males and 11.5% of females).

The prevalence in males was highest in the 10-14 years age group, whereas in females it was highest in 15 to 24 years olds (Figure 7). The overall prevalence was 11.4% in children (0 to 14 years) and 9.9% in adults (15 years and over). During childhood (0 to14 years), prevalence was consistently higher in males. However, from the age of 15 years this was reversed and females demonstrated higher prevalence across all ages. 

Figure 7: Age-specific prevalence rates of current asthma, Australia, 2004-05

Note: 'Current asthma' is based on a positive response to 'have you ever been told by a doctor that you have asthma?' and 'do you still have asthma?'. Source: AIHW analysis of the 2004-05 ABS National Health Survey.

For adults, there is no convincing evidence of any change in the prevalence of asthma during the 1990s. For children, there is consistent evidence of a rise in the prevalence of asthma during the 1980s and into the early 1990s. The most recent data from one study suggest that the rising trend may have peaked and is now levelling off, but this needs to be confirmed in other time series studies. For more information see the AIHW and ACAM (Australian Centre for Asthma Monitoring) publication Asthma in Australia 2005.

Chronic obstructive pulmonary disease

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The prevalence of chronic obstructive pulmonary disease (COPD) is not measured in the National Health Surveys. The best estimate of its prevalence is a combination of self-reported bronchitis and emphysema.  

About 3.3% of Australians reported having bronchitis and/or emphysema in the 2004-05 NHS, compared to3.5% in 2001, 4.1% in 1995 and 3.0% in 1989. Although these estimates would contain some cases of bronchitis that were not chronic in nature, it is still likely to have underestimated the true prevalence of COPD in Australia. This is because COPD is usually not diagnosed until it begins to restrict a person's lifestyle and is moderately advanced. 

The prevalence is slightly higher among females than males at younger ages, but this situation is reversed after age 65. The prevalence of bronchitis/emphysema rises with age, to nearly 10% at the age of 75 years and over (Figure 8).

Figure 8: Age-specific prevalence rates of COPD, Australia, 2004-05

Source: AIHW analysis of the 2004-05 ABS National Health Survey.

Chronic kidney disease

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The incidence and prevalence of chronic kidney disease are difficult to measure. The most severe outcome of chronic kidney disease is end-stage kidney disease (ESKD), when the patient requires kidney replacement therapy , either dialysis or kidney transplant. Information about people beginning and continuing with kidney replacement therapy are reported by the Australian and New Zealand Dialysis and Transplant Registry (ANZDATA), and this can be used to estimate incidence and prevalence of ESKD.   

According to ANZDATA, 1,950 persons (1,175 males and 775 females) began treatment for ESKD in 2004, compared with 556 in 1981. There were 14,221 patients (707 per million) receiving renal replacement therapy (RRT) at 31^st December 2004.  The average age of patients beginning treatment in 2004 was 59.5 years; well above the average of 42.3 years in 1981.  

The incidence of ESKD below the age of 45 was stable between 1981 and 2004 but for the age group 45-64 the incidence increased by 50% (from 10 to 15 per 100,000 population). During this period, incidence in the age group 65-74 increased nine fold (from 4 to 36 per 100,000). For the oldest age group (75 and above), the reported incidence of ESKD, low until 1992, was 30 per 100,000 in 2002 and increased to 31 per 100,000 in 2004 (Figure 9). The increasing prevalence of diabetes is a major contributor to this rise in ESKD incidence.

Figure 9: Trends in the incidence of ESKD^(a), Australia, 1981 to 2004

Note: (a) New cases of kidney replacement therapy. Source: ANZDATA Registry.

At the end of 2004, a total of 14,221 patients (70.7 per 100,000) registered with ANZDATA were receiving Kidney replacement therapy (dialysis or transplantation). Of these, 6,269 (31.2 per 100,000) had a functioning kidney transplant and 7,952 (39.5 per 100,000) received dialysis treatment.   

In 2004, the prevalence was higher in males (89 per 100,000) than in females (61 per 100,000). ESKD prevalence increases rapidly with age, being the highest (201 per 100,000) among those aged 65-74 in 2004. 

The prevalence rate of ESKD has almost tripled over the past 25 years from 24 per 100,000 persons to 71 per 100,000 in 2004 (Figure 10). While some of this increase may be attributed to a higher incidence of kidney failure, improved management of other illnesses and new technologies are also likely to have contributed to these numbers by increasing patient survival.

Figure 10: Trends in prevalence of ESKD, Australia, 1981 to 2004

Note: Age-standardised to the  Australian population as at June 2001. Source: ANZDATA Registry.

Oral diseases  

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Dental problems are very common in the Australian population, but recent data on these is lacking. Two indicators of the prevalence of dental problems are the number of decayed, missing and filled teeth (dmft for deciduous teeth, DMFT for permanent teeth) and edentulism (the loss of all natural teeth).

According to the 2002 National Child Dental Health Survey, the average numbers of dmft/DMFT for 5 and 12-year-old children were 1.45 and 0.41 respectively. 

Tooth decay among children has declined over the levels first observed in 1977, but it is now apparent that dental improvements have stalled in older children and that the caries experience of younger children is increasing. The average dmft for 5- to 10-year-olds improved markedly between 1989 and 1996, but between 1996 and 1999 it increased for all but the 9- and 10-year-olds . DMFT scores  increased in all age groups between 2000 and 2001; the highest increase was for 5-year-olds (Figure 11).

In 2001 the DMFT experienced by 12 year olds was 1.0 and for 15 year olds was 2.2. Between 1990 and 1999, the mean DMFT scores declined for both 12- and 15-year-olds (from 1.4 to 0.8 for the 12 year olds, and from 3.5 to 1.9 for the 15 year olds). Since then the mean DMFT scores has increased to 1.0 and 2.2 respectively for 12- and 15-year-olds (Source: AIHW Dental statistics and research unit, various years).

Figure 11: Trends in average number of decayed, missing or filled deciduous teeth (dmft), Australia, 1990 to 2001

Sources: Child Dental Health Surveys.

Based on the 2002 National Dental Telephone Interview Survey, the prevalence of edentulism among Australians aged 15 years and over was 8.7%. In 1979, approximately one-fifth (20.5%) of individuals aged 15 or older were edentulous, indicating that the prevalence of edentulism has declined considerably in Australia during the last three decades. 

While edentulism was consistently greater in older age groups, downward trends have been observed across all age groups (Figure 12). Some of this decline is explained by changing dental treatment approaches over the past half-century, during which patients and dentists increasingly chose to treat dental diseases by means other than extraction.

Figure 12: Trends in edentulism, Australia, 1979 to 2002

Source: National Oral Health Surveys; National Dental Telephone Surveys.

Arthritis

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The ABS 2004-05 National Health Survey found that about 3 million Australians, 15.3% of the population, suffered from some form of arthritis, with about 60% being females. Of this total, 1.5 million had osteoarthritis and 490,997 had rheumatoid arthritis, with prevalence rates of 7.9% and 2.5% respectively. 

Arthritis is more common among females compared to males. The prevalence rates of both osteoarthritis and rheumatoid arthritis increase with age, and are highest among those aged 65 and above (Figure 13). 

Figure 13: Age-specific prevalence of osteoarthritis and rheumatoid arthritis, Australia, 2004-05

Source: AIHW analysis of ABS 2004-05 National Health Survey.

Osteoporosis

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Nearly 600,000 (3%) of Australian reported having osteoporosis in the 2004-05 National Health Survey.  However, the data based on self-reports are likely to underestimate the actual prevalence because osteoporosis is often not diagnosed until a fracture (a consequence of osteoporosis) occurs. 

A much larger estimate of the prevalence of osteoporosis has been produced by Access Economics, by including proportions of those reporting (as a result of a fracture) back problems, curvature of the spine, other musculoskeletal diseases, as well as fractures from injuries, and osteoporosis from secondary sources. This method produces an estimate of 1.8 million people with osteoporosis in 1995.

Self-reported osteoporosis is markedly more prevalent in females compared to males. Prevalence of osteoporosis is also strongly age-related (Figure 14). Among females, the prevalence was 19.3% in those aged 65-74, increasing to 26.2% in those aged 75 and over. Comparable rates among males were 3.8% and 4.7% respectively. 

Figure 14: Age-specific prevalence of osteoporosis, Australia, 2004-05

Source: AIHW analysis of ABS 2004-05 National Health Survey.

Last reviewed by on 9 July 2007