Many illnesses and health conditions can be classified under the broad heading of chronic disease. Chronic diseases are mostly characterised by:

• complex causality,
• multiple risk factors,
• long latency periods,
• a prolonged course of illness, and 
• functional impairment or disability

Most chronic diseases do not resolve spontaneously, and are generally not cured completely. Some can be immediately life-threatening, such as heart attack and stroke. Others can persist over time and can be intensive in terms of management (e.g. diabetes). Most chronic diseases persist in an individual through life, but are not always the cause of death (e.g. arthritis).

While some chronic diseases such as diabetes and arthritis have been known for centuries, infectious diseases dominated the health scene until the 19th century. For various reasons, including the fact that more people are living to older age and improvements in the treatment and management, chronic diseases have increased in prevalence over the past.

Focus conditions

There are many conditions and illness that can be considered chronic. Recent focus in surveillance of chronic disease has been on 12 chronic conditions identified in the National Public Health Partnership's paper, Preventing chronic disease: a strategic framework. These conditions pose a significant burden in terms of morbidity, mortality and health care costs in Australia, and are amenable to preventive measures. The conditions are:

• Ischaemic heart disease (also known as coronary heart disease)
• Stroke
• Lung cancer
• Colorectal cancer
• Depression
• Type 2 diabetes
• Arthritis
• Osteoporosis
• Asthma
• Chronic obstructive pulmonary disease (COPD)
• Chronic kidney disease
• Oral disease

How many people have chronic disease?

AIHW analysis of the 2004-05 National Health Survey showed that just over 7 million people have at least one chronic condition, and the proportions having a condition increase with age, as do the proportions of people reporting more than one chronic condition.

Proportion (%) of chronic conditions reported, by age, 2004-05
Number of chronic conditions	Age group 0-14	Age group 15-24	Age group 25-44	Age group 5-64	Age group 65 plus
None	86.9	80.8	74.0	47.0	18.4
One	12.3	17.0	21.0	32.0	32.0
Two	0.8	1.9	3.8	14.1	26.7
Three	-	0.3	1.1	5.1	15.3
Four	-	-	0.2	1.4	5.0
Five or more	-	-	-	0.5	2.6

Source: AIHW analysis of the 2004-05 National Health SurveySome other facts about chronic disease

• In 2006-07, arthritis, diabetes and depression were chronic conditions commonly managed at GP consultations (each accounted for 2.5% of all consultations). See Australia's Health 2008
• More than half of all potentially preventable hospitalisations are from selected chronic conditions. In 2007-08, 19.24 (per 1,000 separations) were for chronic conditions such as diabetes, asthma, angina, hypertension, congestive heart failure and COPD. See Australian Hospital Statistics 2007-08
• Ischaemic heart disease, cerebrovascular disease (mainly stroke), lung cancers, COPD and and colorectal cancer all featured in the top 10 leading causes of death in 2005. See Australia's Health 2008
• Indigenous Australians experience higher levels of certain chronic conditions than non-Indigenous Australians. In 2004-05, more Indigenous Australians experienced hypertensive disease, other diseases of the heart and circulatory system, asthma, diabetes, arthritis and kidney disease. See Indigenous Health
• In 2004-05, people with chronic disease were more likely to not participate in the labour force, were less likely to be employed full-time, and more likely to be unemployed, than those without chronic disease. See Chronic disease and participation in work

Referenced from:http://www.aihw.gov.au/cdarf/index.cfm