2. TOPIC
CAUSATION AND SCREENING OF DISEASE IN
EPIDEMIOLOGY
Theory and models of disease causation.
Determinants of disease.
Screening of disease.
3. CAUSATION AND SCREENING OF DISEASE IN
EPIDEMIOLOGY
• Disease is a dynamic process and it is just opposite
to health.
• Disease is the condition by which body health is
impaired, a departure from a state of health, an
alteration of the human body interrupting the
performance of body function.
4. Theory and models of disease causation: -
1) Germ Theory: -
• The germ theory became popular in early 20th
century.
• According to this theory, there is one single
specific micro- organism to every disease.
• This refers to one- to- one relationship between
the causative agent and the disease.
• This is also called as single cause theory.
5. Theory and models of disease causation: -
2) Epidemiological Triad Theory: -
• It was not only the causative agent that was
responsible for causing disease but also host
and environment contribute to the occurrence of
disease.
• This theory consists of three components
Agent
Host
Environment.
6. Theory and models of disease causation: -
Agent: - The agent is considered as primary factor
without which a particular disease cannot
occur.
Host: - The host refers to human beings which
come in contact with the agent.
Environment: It facilitates the interaction of host and
agent.
7. Theory and models of disease causation: -
3) Multifactorial Causation Theory: -
• The diseases are caused by multiple factors.
• This model helps the epidemiologist to
understand the various associative causative
factors, prioritize these and plan preventive and
control measures for a particular disease.
8. Theory and models of disease causation: -
4) Web of Causation theory: -
• This epidemiological model suggests that there
are cluster of causes and combination of effects
which are related to each other and need to
studied to identify possible interventions to
reduce the occurrence of a particular disease.
9. Theory and models of disease causation: -
5) Dever’s Epidemiological Model: -
• This model composed of four major categories
or factors such as human biology, lifestyle,
environment and healthcare system.
• All these factors influence health status either
positively or negatively.
10. DETERMINANTS OF DISEASE
• There are three elements classified as agent,
host and environment which are determinants
or responsible for causation of disease.
1) Agent Factors: -
• The disease agent is defined as an element, a
substance, living or non- living or a force-
11. DETERMINANTS OF DISEASE
intangible, the presence and absence of which may
follow the effective contact with the susceptible
contact or susceptible human host under proper
environmental conditions; it serve as a stimulus to
initiate or perpetuate a disease process.
12. DETERMINANTS OF DISEASE
• The disease agents are usually classified:
Biological Agents
Nutrient Agents
Physical Agent
Chemical Agent
Mechanical Agent
Social Agent
13. DETERMINANTS OF DISEASE
2) Host Risk Factors: -
Demographic characteristics
Biological factors
Psychosocial and economic characteristics.
Life style.
Past history of exposure.
14. DETERMINANTS OF DISEASE
3) Environmental Risk Factors: -
Biological environment.
Physical environment.
Psycho- social environment.
15. SCREENING OF DISEASE
• Screening is testing for infection or disease in
population or in individuals who are not seeking
health care.
• Example, serological testing for AIDS virus in
blood donors, neonatal screening etc.
16. SCREENING OF DISEASE
Aims and objectives of screening: -
• To sort out from a large group apparently
healthy persons likely to have the disease.
• To bring those who are apparently abnormal
under medical supervision and talent.
17. SCREENING OF DISEASE
Uses of screening: -
• Case detection: People are screened for their own
benefit, like cancer, diabetes, hypertension, etc.
• Control of disease: - It is prospective screening that
people are screened for the benefit of others, HIV
etc.
18. SCREENING OF DISEASE
Uses of screening: -
• Research purposes: - To know the natural
history of a disease.
• Educational opportunities – It helps in public
awareness about the disease.
19. SCREENING OF DISEASE
Types of Screening: -
• Mass screening: -
It is the screening of whole population or a
subgroup to analysis whether or not exposed to
the risk of having disease under study.
20. SCREENING OF DISEASE
Types of Screening: -
High risk or selective screening: -
In this screening only those who are at risk
to have a particular problem or disease.
21. SCREENING OF DISEASE
Types of Screening: -
• Multi- phase screening: -
It is the application of two or more screening
test combining to a large number of people at
one time than to carry out the separate
screening tests for single disease.
22. SCREENING OF DISEASE
Types of Screening: -
• Multipurpose screening: -
The screening of a population by more than one
test done simultaneously to detect more than
one disease.
23. SCREENING OF DISEASE
Types of Screening: -
• Case – Finding screening: -
The main objective is to detect disease and bring
patients to treatment.
24. EVALUATION OF SCREENING PROGRAMME
The screening programmes must be put into practice after
proper evaluation by the following ways:
1) Methods:
Experimental method: It conducts RCT of the screening test
to compare the disease specific cumulative mortality rate
between the intervention and control group.
25. EVALUATION OF SCREENING PROGRAMME
Non- experimental method: There are methods like
case control, cohort study and ecological study.
2) Measures of Effect:
Comparison of survival experience.
Comparison of disease specific mortality rate.
