2. 1. Introduction to Epidemiology
Definitions :
Health: A state of complete physical, mental and
social well-being and not merely the absence of
disease or infirmity.
Disease: A physiological or psychological dysfunction.
Illness: A subjective state of not being well.
Sickness: A state of social dysfunction.
3. Public health
The science & art of
Preventing disease,
prolonging life,
promoting health & efficiency
through organized community effort.
4. Epidemiology
“It is the study of frequency, distribution, and
determinants of diseases and other health-related
conditions in a human population
and
the application of this study to the prevention of disease
and promotion of health “
5. Components of the definition
1.Study: Systematic collection, analysis and
interpretation of data
Epidemiology involves collection, analysis and
interpretation of health related data
6. 2. Frequency: the number of times an event occurs
Epidemiology studies the number of times a disease
occurs
It answers the question How many?
7. 4. Determinants: Factors the presence/absence of
which affect the occurrence and level of an event.
Epidemiology studies what determines health events
It answers the question how and why?
8. 5. Diseases & other health related events
Epidemiology is not only the study of diseases
The focus of Epidemiology are not only patients
It studies all health related conditions
11. Purpose/use of Epidemiology
The ultimate purpose of Epidemiology is prevention of
diseases and promotion of health
How?
1. Elucidation of natural history of diseases
2.Description of health status of population
3. Establishing determinants of diseases
4. Evaluation of intervention effectiveness
12. Types of Epidemiology
Two major categories of Epidemiology
1.Descriptive Epidemiology
Defines frequency and distribution of diseases and
other health related events
Answers the four major questions: how many, who,
where, and when?
13. 2. Analytic Epidemiology
Analyses determinants of health problems
Answers two other major questions: how? and why?
Generally, Epidemiology answers six major questions:
how many, who, where, when, how and why?
15. Basic features of Epidemiology
1. Studies are conducted on human population
2. It examines patterns of events in people
3. Can establish cause-effect relationship without the
knowledge of biological mechanism
4. It covers a wide range of conditions
5. It is an advancing science
17. Descriptive epidemiology
It is the study of occurrence and distribution of a
disease i.e. time place and people affected.
Analytical epidemiology
It is concerned with the study of a disease in respect of
its source of origin, route of administration and its
extent of spread.
The study has two types
Case control study (Retrospective study)
Cohort study (Prospective study)
19. Uses of epidemiology
Important uses of epidemiology are
It provides a means to study disease profiles and trends in
human population.
It is useful in community diagnosis.
It makes possible to know the types of diseases prevalent
in a community.
It is useful in planning and evaluation of health services.
Epidemiology gives the complete picture of disease in a
population.
These studies identify the causes of disease and risk
factors.
21. Dynamics of disease transmission
A communicable disease is one in which causative
organism may pass or be carried from one person to
another or one animal to another, either directly or
indirectly.
Source and Reservoir
The source of infection may be a person, animal,
object or substance from which an infective agent
passes to the host.
Reservoir is the natural habital of the infective
organism.
22. Carrier
Infected person or animal that harbors a specific
infectious agent in the absence of disease and serves as
potential source of infection for others.
23. Modes of transmission
A. Direct transmission
1. Direct contact
2. Droplet infection
3. Contact with soil
24. B. Indirect transmission
This includes 5 F’s (flies, fingers, fomites, food and
fluid)
Indirect transmission may be inanimate or animate.
Inanimate
i. Fomites born
ii. vehicle born
iii. Air borne
iv. Hands and fingers
27. Principles of disease control and
prevention
Three essential components in the chain of infection
are source or reservoir, mode of transmission and
susceptible host.
Disease control involves all measures to prevent or
reduce the incidence, prevalence and consequence of
disease.
28. Controlling the reservoir
The simplest method of controlling the reservoir is
elimination of reservoir or source.
General measures of reservoir control in humans include:
Early diagnosis
Notification
Epidemiological investigation
Isolation
Treatment
quarantine
29. Interruption of transmission
Chain of transmission is broken.
Treatment of polluted water can interrupt
transmission of many diseases.
Adequate cooking can prevent transmission of food
borne diseases
Vector control includes control of cattle, pets and
other animals.
30. The susceptible host
The susceptible host can be protected by
i. Active immunization
ii. Passive immunization
iii. Combination of both
iv. Chemoprophylaxis
v. Non specific measures
31. The cause of a disease
An event, a condition or a characteristic that comes
before the disease and without which the disease
wouldn’t occur
32. Example: the disease will not occur without the
presence of the factor
Example: Mycobacterium TB for TB
33. Etiology of a disease
The sum of all factors contribution to the occurrence of
a disease
Agent factors +Host factors +Environmental factors =
Etiology of a disease
34. Levels of disease prevention
Three major levels of disease prevention
1. Primary prevention
Targeted at healthy people
Objectives are Promotion of health
Prevention of exposure and
Prevention of disease
35. 2. Secondary prevention
Targeted at sick individuals
Objective is to stop or slow the progression of disease
and to prevent or limit permanent damage through early
detection & treatment
36. 3. Tertiary prevention
Targeted at people with chronic diseases & disabilities
that can’t be cured
Objective is to prevent further disability or death and
to limit impacts of disability through rehabilitation
37. Factors which influence the
development of disease
Strain of the agent
Dose of the agent
Route of infection
Host age, nutritional status, immune status
Influence of treatment
Influence of season
38. What are measures of disease
occurrence?
These are measurements of the
frequency/magnitude/amount
of disease
in populations
39. How do we measure diseases?
Four quantitative descriptors
Numbers
Ratios
Proportions
Rates
40. Numbers: Use of actual number of events
e.g 100 cases of TB in community A
Ratios: Quantifies the magnitude of one occurrence X,
in relation to another event Y as X/Y
e.g Ratio of TB cases in community A to B is 1:10
41. Proportions: a ratio in which the numerator is included
in the denominator
e.g proportion of TB cases in community A is 10%
Rates: a proportion with time element
It measure the occurrence of an event overtime
