2. EPIDEMIOLOGY
INTRODUCTION
• Epidemiology is the basic science of preventive and
social medicine. Although of ancient lineage, it made
only slow progress up to the start of 20th century.
• Epidemiology has evolved rapidly during the past few
decades. Its ramifications cover not only study of
disease distribution and causation (and thereby
prevention), but also health and health-related events
occurring in human population.
3. • Modern epidemiology has entered the most exciting
phase of its evolution. By identifying risk factors of
chronic disease, evaluating treatment modalities and
health services, it has provided new opportunities for
prevention, treatment, planning and improving the
effectiveness and efficiency of health services.
7. • There appears to be almost as many definitions of
epidemiology as there are authors who have written on the
subject, ranging from Hippocrates to those of the present day. A
short list is given below :
1. That branch of medical science which treats epidemics (Parkin,
1873).
2. The science of the mass phenomena of infectious diseases
(Frost, 1927).
3. The study of disease, any disease, as a mass phenomenon
(Greenwood, 1934), and
• 4. The study of the distribution and determinants of disease
frequency in man (MacMahon, 1960).
8. DEFINITION
• Epidemiology has been defined by John M. Last
in 1988 as:
"The study of the distribution and
determinants of health-related states or events
in specified populations, and the application of
this study to the control of health”.
9.
10. AIMS OF EPIDEMIOLOGY
(Acc. to International Epidemiological Association)
1. To describe the distribution and magnitude of health and
disease problems in human population.
2. To identify etiological factors (risk factors) in the
pathogenesis of disease.
3. To provide data essential to the planning,
implementation and evaluation of services for the
prevention, control and treatment of disease and
setting priorities among those services.
11. ULTIMATE AIM OF EPIDEMIOLOGY
1. To eliminate or reduce the health problems of
community.
2. To promote the health and well-being of society as a
whole.
13. 1. DISEASE FREQUENCY
• Refers to the measurement of health related event in the
form of rates & ratios.
• E.g.. Prevalence rate, Incidence rates, Death rate etc.
• These rates are essential for comparing the disease
frequency in different populations or sub groups of the same
population
14. 2. DISTRIBUTION OF DISEASE
• The basic tenet of epidemiology is that the distribution of
disease occurs in patterns in a community.
• An important function is to study the pattern of the distribution
in various subgroups.
• Thus epidemiology examines whether there has been an
increase or decrease over time span.
• An important outcome of this step is formulation of etiological
hypothesis
15. 3. DETERMINANTS OF DISEASE
A unique feature of epidemiology is to test
etiological hypotheses and identify the
underlying causes(or risk factors) of disease.
16. Q & A
• In the definition of epidemiology, “distribution” refers to:
– Who
– When
– Where
– Why
• In the definition of epidemiology, “determinants” generally
includes:
– Agents
– Causes
– Control measures
– Risk factors
– Sources
17. Q & A
• In the definition of epidemiology, “distribution” refers to:
– Who
– When
– Where
– Why
• In the definition of epidemiology, “determinants” generally
includes:
– Agents
– Causes
– Control measures
– Risk factors
– Sources
18. Epidemiologists are interested in learning
about ____________________ .
a)the causes of diseases and how to cure or
control them
b)the frequency and geographic distribution of
diseases
c)the causal relationships between diseases
d)all of the above
19. Epidemiologists are interested in learning
about ____________________ .
a)the causes of diseases and how to cure or
control them
b)the frequency and geographic distribution of
diseases
c)the causal relationships between diseases
d)all of the above
20. SCOPE OF EPIDEMIOLOGY
1. Causation of the disease.
2. Natural history of the disease.
3. Health status of the population.
4. Evaluation of Interventions.
21. 1. Causation of the disease.
• Most of diseases are caused by interaction between genetic,
environmental factors and personal behaviors affect this
interplay.
• Epidemiology is used to study their influence and the effects
of preventive interventions through health promotion.
22. 2. Natural history of the disease
Epidemiology is also concerned with
the course and outcome (natural history) of diseases in
individuals and groups.
23. 3. Health status of the population
• Epidemiology is often used to describe the health status of
population.
• Knowledge of the disease burden in populations is
essential for health authorities.
• To use limited resources to the best possible effect by
identifying priority health programmes for prevention and
care.
24. 4. Evaluation of Interventions
• To evaluate the effectiveness and efficiency of health services.
• This means determining things such as –
- Impact of contraceptive use on population Control.
- the efficiency of sanitation measures to control diarrheal diseases
and
- the impact of reducing lead additives in petrol.
25. USES OF EPIDEMIOLOGY
1. To study historically the rise and fall of disease in the
population:
Winston Churchill said · "The farther back you look, the
farther forward you can see". The first use of epidemiology
relates to this aspect, that study of the history of disease in
human population. It is well known that the health and
disease pattern in a community is never constant.
26. 2. Community diagnosis
Community diagnosis generally refers to the
identification and quantification of health problems in a
community in terms of mortality and morbidity rates and
ratios, and identification of their correlates for the purpose
of defining those individuals or groups at risk or those in
need of health care.
By quantification of health problems, we lay down
priorities in disease control and prevention.
27. • Secondly, quantification of morbidity and mortality can serve
as a benchmark for the evaluation of health services at a later
date.
• Thirdly, the quantification of health problems can be a source
of new knowledge about disease distribution, causation and
prevention.
28. 3. Planning and evaluation :
Planning is essential for a rational allocation of the limited resources.
For example, in developing countries, too many hospitals have been built and
equipped without knowledge of the particular disease problems in the
community.
Examples of planning include planning facilities for medical care
planning facilities for preventive services and planning for research.
Evaluation is an equally important concern of epidemiology. Any
measures taken to control or prevent any disease must be followed by an
evaluation to find out whether the measures undertaken are effective in
reducing the frequency of the disease.
29. 4. Evaluation of individual's risks and chances
One of the important tasks of epidemiologists is
to make a statement about the degree of risk in a
population.
Besides the incidence rate and specific rates which
are measures of absolute risk, the epidemiologists
calculate relative risk and attributable risk for a factor
related to or believed to be a cause of the disease.
30. 5. Syndrome identification
Medical syndromes are identified by observing
frequently associated findings in individual patients. It
is worth recalling that, although approximately 3000
so-called syndromes are described in the
contemporary paediatric literature, a primary defect is
known only in about 20 per cent of these .
Epidemiological investigations can be used to define
and refine syndromes.
31. 6. Completing the natural history of disease
Epidemiology is concerned with the entire
spectrum of disease in a population. The picture of
disease constructed on the basis of hospital patients is
quite different from that found in the community.
The epidemiologist by studying disease patterns
in the community in relation to agent, host and
environmental factors is in a better position to fill up
the gaps in the natural history of disease than the
clinician.
32. 7.Searching for causes and risk factors
Epidemiology, by relating disease to interpopulation
differences and other attributes of the population or cohorts
examined, tries to identify the causes of disease. The
contributions of epidemiology have been many in this regard.
Numerous examples can be cited : epidemiological
studies have incriminated that rubella is the cause of congenital
defects in the newborn, that thalidomide is a teratogenic agent,
cigarette smoking is a cause of lung cancer, exposure of
premature babies to oxygen is the cause of retrolental
fibroplasia, etc.
34. a. Asking questions
Epidemiology has been defined as "a means of
learning or asking questions and getting answers that lead
to further questions" For example, the following questions
could be asked:
RELATED TO HEALTH EVENTS
a. What is the event ? (the problem)
b. What is its magnitude?
c. Where did it happen?
d. When did it happen?
e. Who are affected? f. Why did it happen?
35. RELATED TO HEALTH ACTION
1. What can be done to reduce this problem and its consequences?
2. How can it be prevented in the future?
3. What action should be taken by the community? By the health
services? By other sectors ? Where and for whom these activities be
carried out ?
4. What resources are required? How are the activities to be
organized?
5. What difficulties may arise, and how might they be overcome?
Answer to the above questions may provide clues to disease
aetiology, and help the epidemiologist to guide planning and
evaluation.
36. b. Making comparisons :
The basic approach in epidemiology is to make
comparisons and draw inferences. This may be comparison of
two (or more groups} - one group having the disease (or
exposed to risk factor) and the other group(s) not having the
disease (or not exposed to risk factor}, or comparison
between individuals.
By making comparisons, the epidemiologist tries to find
out the crucial differences in the host and environmental
factors between those affected and not affected.
37. • One of the first considerations before making comparisons is
to ensure what is known as "comparability" between the
study and control groups. In other words, both the groups
should be similar so that "like can be compared with like”
38. BIBLIOGRAPHY
• Park k, “TEXTBOOK OF PREVENTIVE AND SOCIAL
MEDICINE”, 23rd edition, banarasidas bhanot, Jabalpur,
2010,.
• Kamalam. S, “ESSENTIALS IN COMMUNITY HEALTH
NURSING PRACTICE”, 1st edition, 2008 jaypee
brothers, new Delhi,.
• B. T. Basavanthappa “COMMUNITY HEALTH
NURSING”, 1st edition, 2008 jaypee brothers, Mumbai,.
