Epidemiological Triad/ Epidemiological Triangle - Simplified / Community Health Nursing.

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I. Introduction
CONCEPT OF DISEASE
• Concept of diseases is a condition of the body or some part or organ of the body in which its functions are deranged
Disease causation.
• Any event or condition, characteristics or combination of
factors which plays an important role in initiating and
producing a disease process.
Concepts, Models or Theories of Disease causation

In epidemiology, there are several models of disease causation that help understand disease process.
General Models of Causation
The most widely applied general models of causation are:
A. Germ Theory of Disease
B. The Epidemiological Triad (Triangle),
C. Multi-factorial Causation theory
D. The Wheel Model,
E. The Web Model.
F. The Sufficient cause and Component causes Models
G. The Devers Epidemiological Model
H. Others
A. The epidemiological Triad Model
• The epidemiological triad or triangle is the traditional model of infectious or communicable disease causation.
• According to this theory, every one exposed to disease agent did not contract the disease. This means it is not only the causative agent that is responsible for disease but there are other factors also, related to man and environment which contribute to disease.
II. Components of Epidemiological Triad
• For the occurrence of a disease in man three things are required.
The Epidemiological Triad
a) HOST
b) AGENT
c) ENVIRONMENT
d) These three factors are referred as Epidemiological triad
Disease Triangle
Disease develops when all the three
Factors interact.
A. Agent factors
• An Agent is the first link in the chain of disease transmission.
a. Definition
“ The disease agent is defined as a substance, living or non living, a force, tangible or intangible, or a factor whose presence, excessive presence or relative absenceis essential for the occurrence of a disease process such as a micro-organism, chemical substance, or form of radiation etc”.
b. Classification of Agent
1. Biological Agent
2. Physical Agent
3. Chemical Agent
4. Mechanical Agent
5. Social Agent
6. Nutrient Agent
7. Others
B. Host factors
a. Meaning
• A person or animal that affords subsistence or lodgment toan infectious agent under natural conditions.
• Human being is referred to as “soil” and the disease agentas “seed”
b. Host related factors
•Host factors are intrinsic factors that influence an individual’s exposure, susceptibility, or response to a causative agent.
Classification of Host related factors
1. Demographic characteristics
a. Age
b. Sex
2. Biological Characteristics
- Hereditary / Genetic factors
- Biochemical levels - Cholesterol
- Blood groups
- Immunological factors
- Physiological functions - BP
3. Social and Economical Characteristics
a. Socio – economic status
b. Education
c. Nutrition
d. Occupation
e. Stress
f. Marital status
g. Housing etc.
4. Life style factors
- Personality traits
- Living habits
- Custom, tradition culture, habits, etc
- Behavioral patterns
- Physical exercise
- Use of alcohol, drugs & smoking etc.
c. Environmental factors
Environmental factors are extrinsic factors which affect the agent as well as the host and the opportunity for exposure.
Environmental factors include:
i.Physical Environment
- Physical factors, such as geology, climate,
- unsafe water, air, soil, food, housing, etc.
ii. Biologic environment
Biologic factors such as animals, insects, plants, rodentsetc. that transmit an agent.
iii. Social /Sicioeconomic Environment
- Socioeconomic factors such as crowding, sanitation, the
availability of health services, customs, habits, culture,
beliefs, attitude, religions, etc

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