Epidemiologic Mind : Disease Causation, Risk Factor and Primary Causes
Definition
Cause of disease
: is an event, condition, characteristic or a combination of these factors
which plays an important role in producing the disease.
The causes of disease can be classified in to two:
1. Primary causes –
these are the factors which are necessary for a disease to occur, in whose absence the disease will not occur. The term ”etiologic agent” can be used instead of primary
cause for Infectious causes of diseases. For example “Mycobacterium
tuberculosis” is the primary cause (etiologic agent) of pulmonary
tuberculosis.
2. Risk factors (contributing, predisposing, or aggravating factors)
.
These are not the necessary causes of disease but they are important for a
disease to occur. A factor associated with an increased occurrence of a
disease is risk factor for the exposed group; and a factor associated with a decreased occurrence of a disease is
a risk factor for the non exposed group. Risk factors could be related to
the agent, the host and the environment.
The etiology of a disease
is the sum total of all the factors (primary causes and risk factors) which
contribute to the occurrence of the disease.
It is the interaction of the agent, the host, and the environment which
determines whether or not a disease develops, and this can be illustrated
using the epidemiologic triangle.
The Epidemiologic Triangle
The epidemiologic triangle, depicts the relationship among three key factors in the occurrence of disease or injury:agent, environment, and host An agent is a factor whose presence or absence, excess or deficit is necessary for a particular disease or injury to occur.
The environment includes all external factors, other than the agent, that can influence health. These factors are further categorized according to whether they belong in the social, physical, or biological environments.
The social environment encompasses a broad range of factors, including education, unemployment, culture regarding diet; and many other factors pertaining to political, legal, economic, communications, transportation, and health care systems.
Physical environmental factors are factors like climate, terrain, and pollution.
Biological environmental influences include vectors, humans and plants serving as reservoirs of infection. From the perspective of epidemiologic triangle, the host, agent, and environment can coexist harmoniously. Disease and injury occur only when there is altered equilibrium between them.
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