Basic Terms in Disease Epidemiology: Non-Communicable Diseases

Non Communicable Diseases (NCDs) are different from infectious diseases in that these diseases do not spread from one person to another by touch. In addition, non-communicable diseases are usually caused by more than one ‘agent’. When we talk about causes of NCDs, we discuss risk factors.

Examples of NCDs are: Cardiovascular diseases (Stroke, Heart Attack, etc.); Cancer, etc.

Risk Factor: The World Health Organization defines a risk factor as “any attribute, characteristic or exposure of an individual that increases the likelihood of developing a disease or injury”.

Why don’t we describe NCDs in terms of ‘agents’?

The origins of the concept of ‘agents’ can be traced to the Germ Theory of Disease. This theory resulted from the discovery of various micro-organisms as the cause of infectious diseases. It suggested that one infectious agent would cause/ result in only one disease, and vice-versa. This is referred to as the ‘one-to-one’ causation theory because of the same reason. However, later discoveries have shown this theory to be an oversimplification. Some infectious agents cause more than one disease; and some diseases are caused by more than infectious agent.

In the early days NCDs were called ‘lifestyle diseases’ because they did not seem to be caused by infectious agents; and many of the ‘rules’ of infectious diseases did not seem to apply to them. In order to better explain this new type of disease, the term risk factor was coined.

Risk factors could include attitudes, behaviours, exposures to substances, etc.

Risk factors are commonly classified as being modifiable or non-modifiable.

Modifiable risk factors: These are attributes that can be changed or altered.

Examples: Smoking habit, Lack of physical activity, etc.

Non-Modifiable risk factors: These attributes cannot be changed/ altered.

Examples: Race, Sex (adult sex-change operations do not change one’s risk), family history, etc.

Modifiable risk factors are altered by the administration of interventions.

Intervention: An act/ treatment/ drug, etc. that is deliberately introduced to change/ modify a situation/ condition.

Examples: Health education, treatment with prescription drugs (medicines), vaccines, etc.

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