Health disease and epidemiology

Epidemiology
3rd yr syllabus
Dr. Saurabh Agrawal

1.1 CONCEPT OF HEALTH AND DISEASE
• WHO definition of health
• Dimensions of health (P M S)
• Concept of well being- obj, sub, standard of
living, QOL

1.2 CONCEPT OF HEALTH AND DISEASE
• Concept of disease
• Concept of causation
• Epidemiological triad
• Natural hist. of disease (risk and other
factors)
• Concept of control
• Concept of prevention
• Mode of intervention

2. EPIDEMIOLOGY
• Concept of epidemiology
• Measurement of epidemiology (Morbidity- incid
and preval) (52)
• Selected Definitions (89)
• Dynamics of disease transmission (91)
• Susceptible host
• Host defences
• Immunizing agent (99)
• Disease prevention and control (111)
• Investigation of epidemic (122)

CONCEPT OF HEALTH
6
 Health is evolved over the centuries as a concept
from individual concern to world wide social goal
and encompasses the whole quality of life.
Changing concept of health till now are:
 Biomedical concept
 Ecological concept
 Psychosocial concept
 Holistic concept

BIOMEDICAL CONCEPT
7
 Traditionally, health has been viewed as an
“absence of disease”, and if one was free from
disease, then the person was considered
healthy.
 This concept has the basis in the “germ theory
of disease”.
 The medical profession viewed the human body
as a machine, disease as a consequence of the
breakdown of the machine and one of the
doctor’s task as repair of the machine.

ECOLOGICAL CONCEPT
8
 Form ecological point of view; health is viewed
as a dynamic equilibrium between human being
and environment, and disease a maladjustment
of the human organism to environment.
 According to Dubos “Health implies the relative
absence of pain and discomfort and a continuous
adaptation and adjustment to the environment
to ensure optimal function.”

PSYCHOSOCIAL CONCEPT
 According to psychosocial concept “health is not
only biomedical phenomenon, but is influenced
by social, psychological, cultural, economic and
political factors of the people concerned.”
9

HOLISTIC CONCEPT
10
 This concept is the synthesis of all the above
concepts.
 It recognizes the strength of social, economic,
political and environmental influences on
health.
 It described health as a unified or multi
dimensional process involving the wellbeing of
whole person in context of his environment .

DEFINITIONS OF HEALTH
 “Health is a state of complete physical, mental,
social well-being and not merely the absence
of disease or infirmity.”
- World Health Organization
 In recent years, this definition has been
amplified to include “the ability to lead socially
and economically productive life”.
11

12
 The WHO definition of health has been
criticized as being too broad. Some argue that
can not be defined as a “state” at all, but must
be seen as a process of continuous adjustment
to the changing demands of living and of the
changing meaning we give to life. It is dynamic
concept. It helps people live well, work well
and enjoy themselves.

13
 It refers to a situation that may exist in some
individuals but not in everyone all the time, it
is not usually observed in a groups of human
beings and in communities. Some consider it
irrelevant to everyday demands, as nobody
qualifies as healthy, i.e., perfect
biological, psychological and social
functioning. That is, if we accept the WHO
definition, we are all sick.

OPERATIONAL DEFINITION
 The WHO definition of health is not an
“operational” definition, i.e. it does not
lend itself to direct measurement,
studies of epidemiology of health have
been hampered because of our
inability to measure health and
wellbeing directly.
14

OPERATIONAL DEFINITION
15
 Broad Sense: Health can be seen as “Acondition
or quality of human organism expressing the
adequate functioning of the organism in given
condition, genetic or environmental.”
 Narrow sense: There is no obvious evidence of
disease, and that a person is functioning
normally. Several organs of the body are
functioning adequately in themselves and in
relation to one another, which implies a kind of
equilibrium or homeostasis.

DIMENSIONS OF HEALTH
Physical Mental Social
Dimensions of
health
Spiritual Emotional Vocational

1.Physical Dimensions :
 Physical health means perfect functioning of the body in which each organ is
working in harmony with the maximum capacity.
 Physical health is achieved by the exercise, healthy diet, adequate rest and sleep
and no smoking or alcohol intake.
 To maintain proper physical health there is need for taking safety precautions,and
regular follow up with the health care providers.
 Signs of physical health :
 A good complexion.
 A clean skin.
 Bright eyes.
 Not too fatty.
 A sweet breath.
 A good appetite.
 Sound sleep.
 Regular activities of bowels and bladder.
 Smooth, easy, and coordinated bodily movements.

Evaluation of Physical Health :
1. Self assessment of overall health.
2. Inquiry about ill health and risk factors.
3. Inquiry in to medications.
4. Standardized questionnaire for cardiovascular and respiratory
diseases.
5. Clinical examinations.
6. Nutritional and dietary history.
7. Biochemical and laboratory investigations.

2.Mental Dimensions :
 Mental health is a state of balance between body and mind .
Earlier the body and mind were considered two separate
entities.
 But these are interrelated as physical illness can result mental
illness and vice versa.
How mental illness influence physical health has been shown in
fig;
Mental illness
DEPRESSION
Poor nutrition
intake
Poor hygiene
Physical
illness
Prone to
infection
Decresed
immune
system

Characteristics of mentally healthy person :
1. Mentally healthy person will be capable of making personal and social
adjustment.
2. Mentally healthy person is free from internal conflicts.
3. He faces problems and tries to solve them intelligently.
4. He has good self control balances rationally and emotionally.
5. He knows him self his needs problems and goals.
6. He has strong sense of self esteem.
7. He serches for identity.
8. He lives a well balanced life means able to maintain the balance
between work rest and recreation.

3.Social Dimensions:
An individual is socially healthy if he is able to maintain
harmonious relationship with other members of society in which he
lives.
Social health rooted in “positive material environment” and
“positive human environment” which is concerned with the social
network of the individual.
The social dimensions of health includes;
 Communication
 Intimacy
 Respect
 Equality
 Social functioning

4. Spiritual Dimensions :
•  Spirituality means in touch with deeper self
and exploring the purpose of life, as people
believe in some force that transcend physiology
and psychology of human beings.
•  It includes love , charity, purpose ,
principles , ethics, intigrity,hope of life.
•  Meditations ,prayers, or spiritual
gatherings are organizedto maintain spiritual
health.

5. Emotional Dimensions :
 Emotional health is closely related to the mental health and is
considered as an important element of health.
 Cognition is related to the mental health whereas emotional health is
related to the feelings of a person.
 Emotional health includes ;
o An emotionally healthy person has a positive thinking and is capable
of coping and adjusting self.
o An emotionally healthy person participates in all the activities which
are related to personal growth and his self esteem.
o Emotionally well people have the ability to express feelings freely
and manage feelings effectively.
o They are also aware of and accept a wide range of feelings in
themselves and others.

6. Vocational Dimension :
 The choice of profession, job satisfaction, career ambitions and
personal performance are all important components of this
dimension.
 To be occupationally well, a person is ultimately doing exactly
with what they want to do in life and are comfortable with their
future plans.
 Vocational dimension of health can be assesed by ;
 Assessing the satisfaction level at job ,
 Facilities attached to the job ,
 Behaviour of the management and administrator and of
colleagues at job.

7.Other dimensions :
 A few other dimensions also suggested such as ;
 Cultural dimensions
 Socio-economic dimensions
 Environmental dimensions
 Educational dimensions
 Nutritional dimensions
 Preventive dimensions

आरोग्यलिङ्ग
अन्नालििाषो िुक्तस्य पररपाकः सुखेन् ।।।६
सृष्टविणमूत्रिातत्िं शरीरस्य । िाघिम ् ।
सुप्रसन्नेद्रियत्िं । सुखस्िप्नप्रबोधननम ् ।।७
बििणाायुषां िािः सौमनस्यं समाग्ग्नता।
विद्यात् आरोग्यलिङ्गानन विपरीते विपयायम ् ८
26

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27

POSITIVE HEALTH
 A person who is healthy physically mentally and socially (and
spiritually) is said to be in a state of “Positive Health” i,’e
Higheststandards of health.
 Conceptualizes health Biologically, as a state in which every
cell and every organ is functioning at optimum capacity and
in perfect harmony with rest of the body
 Physiologically, as a state where the person feels the sense of
perfect wellness and of mastery over his environment.
 Socially, as a state where the persons capacities for
participation in social system are optimal
 Never coming reality

CONCEPT OF WELL BEING
components
Subjective
Quality of life
Objective
Standard of living
Level of living

Standard of living
 Scale of ourexpenditure
 Goods weconsume
 Services weenjoy
 level of education,employment
status, food, dress, house,
 amusements & comforts of modernliving
WHO: "Income and occupation, standards of housing,
sanitation and nutrition, the level of provision of health,
educational, recreational and other services may all be used
individually as measures of socio-economic status, and
collectively as an index of the "standard of living"

Level of living
Parallel term in UN
 Health
 Food consumption
 Education
 Occupation & workingcondition,
 Housing
 Social security
 Clothing
 Human rights

QUALITY OF LIFE
AccWHO
Thecondition of life resulting from combination of the
effects of the complete range of factors such as those
determining health, happiness, education, social and
intellectual attainments, freedom of action, justice and
freedom of expression.
RECENT QOL"a composite measure of physical, mental and social well-being
as perceived by each individual or by group of individuals - that is to say,
happiness, satisfaction and gratification as it is experienced in such life
concerns as health, marriage, family work, financial situation, educational
opportunities, self esteem, creativity, belongingness, and trust in others".

DETERMINANTS
The factors which determine the health of an
individual are many. Some are inside thebody
(genetic) and some are outside the body
(environmental factors).

Determinants of health
Heredity
Health services
 Promotive,
preventive,
curative,
rehabilitative
Environment
 Physical, social,
biological and man-
made
Behavior
 Actions
 Habits
 Reactions
 Belief,
attitudes
 Practices
(Lifestyles)
Health

CONCEPT OF DISEASE
37
 Webster defines disease as “a condition in
which body health is impaired, a departure from
a state of health, an alteration of the human
body interrupting the performance of vital
functions”.
 The oxford English Dictionary defines disease as
“ a condition of the body or some part or organ
of the body in which its functions are disturbed
or deranged”.

CONCEPT OF DISEASE
 Ecological point of view disease is defined as
“a maladjustment of the human organism to
the environment.”
 The simplest definition is that disease is just
the opposite of health: i.e. any deviation from
normal functioning or state of complete
physical or mental well-being.
38

3
9
Definitions
Health: A state of complete physical, mental and social
well-being and not merely the absence of disease or
infirmity (WHO,1948)
Disease: A physiological or psychological dysfunction
Illness: A subjective state of not being well
Sickness: A state of social dysfunction

4
0
Definitions…
Public health
The science & art of
Preventing disease,
prolonging life,
promoting health & efficiency
through organized community effort (Winslow,
1920)

4
1
Definitions…
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

4
2
Components of the
definition
•Study: Systematic collection, analysis and
interpretation of data
Epidemiology involves collection, analysis and
interpretation of health related data
Epidemiology is a science

4
3
Components…
2. Frequency: the number of times an event
occurs
Epidemiology studies the number of times a
disease occurs
It answers the question How many?
Epidemiology is a quantitative science

4
4
Components…
3. Distribution: Distribution of an event by person,
place and time
Epidemiology studies distribution of diseases
It answers the question who, where and when?
Epidemiology describes health events

4
5
Components…
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?
Epidemiology analyzes health events

46
Components…
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
Epidemiology is a broader science

47
Components…
• 6. Human population
• Epidemiology diagnoses and treats
communities/ populations
• Clinical medicine diagnoses and treats
patients
• Epidemiology is a basic science of public
health

48
Components…
7. Application
Epidemiological studies have direct and practical
applications for prevention of diseases &
promotion of health
Epidemiology is a science and practice
Epidemiology is an applied science

4
9
Epidemiology
and
Revise

THEORIES OF DISEASES CAUSATION
50
1. Supernatural theory of disease
 Disease is due to super power e.g. gods, evil
spirits.
2. Tridosha theory of disease
 The doshas or humors are: Vaata (Wind),
Pitta (gall), and Kapha (mucus).
 Perfect balance of tridosha is healthy
 Disturbance in balance is disease

THEORY OF DISEASES CAUSATION
51
3. Theory of Contagion
 Spreading of disease by being close to or
touching other people.
4. Miasmatic theory of disease causation
 Disease is due to noxious air and vapors
 These concepts were prevailing before
Louis Pasteur (1822-1895).

5. Germ Theory of disease
 In 1860, Louis Pasteur demonstrated the
presence of bacteria in air.
 This theory emphasized that the sole cause of
disease is microbes.
 The theory generally referred to as one-to-
one relationship between disease agent and
disease.
Disease agent Man Disease
52

53
6. Epidemiological Triad concept
 The germ theory of disease has many
limitations
 For example it is well – known that not all
exposed to tuberculosis bacilli develops
tuberculosis ,the same condition in an
undernourished person may result in
clinically manifest.

Agent
54
Host
Epidemiological Triad
Environment

MULTI-FACTORIAL ETIOLOGY
55
 The germ theory of disease or single cause of
disease is always not true.
 The germ theory of disease was overshadowed
by multi-factorial cause theory in 19th century.
 As a result of advancement in public
health, communicable diseases began to
decline and are replaced by new type of
diseases so called modern disease of
civilization.

MULTI-FACTORIAL ETIOLOGY
56
 Example: Lung cancer, CHD, Mental illness etc.
The disease could not be explained on the
basis of germ theory of disease and can not be
controlled or prevented on that basis. The
realization began that multiple factors are
responsible for disease causation where there
is no clear single agent.
 The purpose of knowing multiple factors of
disease is to quantify and arrange them in
priority sequence for modification to prevent
particular disease.

WEB OF CAUSATION
57
 This model of disease causation was suggested
by Mac Mohan and Pugh.
 ]This model is ideally suited in the study of
chronic disease where the disease agent is
often not known, but is the outcome of
interaction of multiple factors.
 The web of causation considers all the
predisposing factors of any type and their
complex interaction with each other.

WEB OF CAUSATION
58
 The basic tenets of epidemiology are to study
the clusters of causes and combinations of
efforts and how they relate to each other.
 The web of causation does not imply that the
disease can not be controlled unless all the
multiple causes or chain of causation or at
least a number of them are appropriately
controlled.
 Sometimes, removal of one link may be
sufficient to control disease.

WEB OF DISEASE CAUSATION
41
Changes in life style
Stress
Obesity
HTN
Smoking
Emotional stress
Aging
Changes in the walls
of arteries
Coronary Occlusion
Myocardial ischemia
Hyperlipidemia
Coronary
Atherosclerosis
Myocardial Ischemia
Fig: We b of causation of MI
59

Plan of presentation
 Introduction
 Phases
 Factors
 Risks groups
 Spectrum of disease
 Concepts of prevention
 Modes of intervention

Introduction
The natural course that a disease would take
when it has not been affected by any treatment
or any other intervention. It is of much
importance for all of us to understand the
natural course of human disease.

Phase
1.Prepathogenesis phase
The disease agent has not yet entered
man, but the factors which favour its
interaction with the human host are already
existing in the environment.

2. Pathogenesis phase
The pathogenesis phase begins with the entry
of the disease “agent’’ in the susceptible human
host. The disease agent multiplies and induces
tissue and physiological changes, the disease
progresses through a period of incubation and
later through early and late pathogenesis .

Factors
1.Agent factors
A substance, living or non-living, or a
force, tangible or intangible, the excessive
presence or relative lack of which may
initiate or perpetuate a disease process.

Agents
• 1. Biological
• 2. Nutrient
• 3. Physical
• 4. Chemical
• 5. Mechanical
• 6. Absence/ insufficiency
of necessary facs. For
health
• 7. Social

Contd…………
 Biological agents:
These are living agents of disease, viruses,
rickettsiae, fungi, bacteria, protozoa and metazoa.
These agents exhibit certain “host-related”
Biological properties such as:
 Infectivity:
This is the ability of an infectious agent to invade
and multiply in a host:

Cont…
 Pathogenicity : This is the ability to induce
clinically apparent illness..
 Virulence: the proportion of clinical cases
resulting in severe clinical manifestations.
Measured by case fatality rate

Nutrient agents:- These are proteins, fats,
carbohydrate, minerals and water. Any excess or
deficiency of the intake of nutritive elements may
result in nutritional disorders. e.g. Anaemia, goitre,
obesity and vitamin deficiencies are some of the
current nutritional problems in many countries.
Physical agents:-Exposure to excessive heat, cold,
humidity, pressure, radiation, electricity, sound.

Contd….
Chemical agents :-
o Endogenous: e. g. Ureamia, jaundice, ketosis.
o Exogenous : e. g. allergens, metals, fumes.
Mechanical agents:- Exposure of chronic friction
and other mechanical forces may result in crushing,
tearing, sprains, dislocations and even death.

Cont…..
Absence or insufficiency necessary or excess of
a factor to health
These may be:
(i) Chemical factors (hormones, enzymes)
(ii) Nutrient factors
(iii) chromosomal factors (mongolism, turners, down)
(iv) Immunological factors.
(v) Lack of part (thymus)
(vi) Lack of structure (cardiac anomalies)

Social agents:- It is also necessary to consider
agents of disease. These are poverty, smoking, abuse
of drugs and alcohol, unhealthy lifestyles, social
isolation, maternal deprivation

2 Host factors
The human host is referred to as “soil” and the
disease agent as “seed” . In some situations,
host factors play a major role in determining
the outcome of an individuals exposure to
infection.eg. Tuberculosis.
The host factors may be classified as;
 Demographic (age, sex, ethnicity)
 Biological (gene facs, biochem, physiologial)

cont…
 Social and economic characteristics such as
socioeconomic status, education, occupation,
stress , marital status , housing, etc.
 Lifestyle factors such as personality traits ,
living habits, nutrition, physical exercise, use
of alcohol, drugs and smoking, behavioral
patterns.

3 Environmental factors
For human beings the environment is not limited, as it
normally is for plants and animals, to a set of climatic
factors.
For Example, for man, social and economic
conditions are more important than the mean annual
temperature.

Cont….
 Physical
 Biological
 Psychosocial.
 Physical environment:
The term “physical environment” is applied
to non-living things and physical factors (e.g..
Air, water, soil, housing, climate, geography,
heat, light, noise, debris & radiation)

Cont….
Biological environment:- The biological
environment is the universe of living things which
surrounds man, including man himself. The living
things are the viruses and other microbial agents,
insects, rodents animals and plants
 Psychosocial environment:- “Those factors
health,affecting personal
community
health
stem
psychosocial
well-being that
make-up of individuals
care and
from the
and the
structure and functions of social groups.”

Risk factor
a. An attribute or exposure that is significantly
associated with the development of a disease.
b. A determinant that can be modified by
intervention, thereby reducing the possibility
of occurrence of disease or other specified
outcomes.

Risk groups
Biological situation:
• age group, e.g., infants (low birth weight),
toddlers, elderly
• sex, e.g., females in the reproductive age
period
• physiological state, e.g., pregnancy,
cholesterol level, high blood pressure
• genetic factors, e.g., family history of genetic
disorders

Cont…
b. Physical situation:
• Rural, urban slums
• Living conditions , overcrowding
• Environment: water supply, proximity to industries
c. Sociocultural and cultural situation:
•
•
•
•
Social class
Ethnic and cultural group
Family disruption. Education, housing
Customs, habits and behavior
• Lifestyles and attitudes
• Access to health services

Spectrum of disease
The term “spectrum of disease” is a graphic representation
of variations in the manifestations of disease.
Iceberg of disease
The floating tip of the iceberg represents what the physician
sees in the community, i.e., clinical cases. The cast
submerged portion of the iceberg represents the hidden
mass of disease, i.e., latent, inapparent, presymptomatic
and undiagnosed cases and carriers in the community.
The “waterline” represents the demarcation between
apparent and inapparent disease.

Symptomatic disease
( what the physician sees)
Pre-symptomatic disease
(what the physician does not see)

Concept of control.
Disease control
The term "disease control" describes (ongoing) operations
aimed at reducing:
i. the incidence of disease
ii. the duration of disease, and consequently the risk of
transmission
iii. the effects of infection, including both the physical and
psychosocial complications; and
iv. the financial burden to the community.

Steps of control
1. Disease elimination
2. Disease eradication
3. Monitoring and surveillance
4. Sentinel surveillance
5. Evaluation of control

1. Disease elimination
• Between control and eradication, an
intermediate goal is described as “Regional
elimination”
• Describes interruption of transmission of
disease
• Eg. Elimination of Measels, Polio from some
region of geography

2. Disease eradication
• Implies termination of all infection by
extermination of infectious agent.
• Cessation of infection and disease from the
whole world
• Smallpox is eradicated

3. Monitoring and Surveillance
• The performance and analysis of routine
measurements aimed at detecting changes in
environment or health status of population
• Monitoring becomes one specific and essential part of
the broader concept embraced by surveillance.
Monitoring requires careful planning and the use of
standardized procedures and methods of data
collection, and can then be carried out over extended
periods of time by technicians and automated
instrumentation.
• Surveillance, in contrast, requires professional
analysis and sophisticated judgment of data leading
to recommendations for control activities.

4 . Sentinel surveillance
• used when high-quality data are needed
about a particular disease that cannot be
obtained through a passive system.
• most passive surveillance systems receive data
from as many health workers or health
facilities as possible, a sentinel system
deliberately involves only a limited network of
carefully selected reporting sites

• The following criteria should be considered in
selecting a sentinel health facility (usually a
general or infectious disease hospital) :
• It should be willing to participate.
• It serves a relatively large population that has
easy access to it.
• It has medical staff sufficiently specialized to
diagnoze, treat and report cases of the disease
under surveillance.
• It has a high-quality diagnostic laboratory.

5. Evaluation of Control
• Process of assessing of how well and program
is performing
• Should be considered during planning and
implementation
• Useful for
– Derived benefits
– Indentify performance difficulties

Concepts of prevention
1. Primordial prevention
2. Primary prevention
3. Secondary prevention
4. Tertiary prevention

1. Primordial prevention
In primordial prevention, efforts are directed towards
discouraging children from adopting harmful lifestyles.
2. Primary prevention
“Action taken prior to the onset of disease which removes
the possibility that a disease will ever occur”.
The WHO has recommended the following approaches
for the primary prevention of chronic diseases where the
risk factors are established:
a. population (mass) strategy
b. high-risk strategy

Cont…
3. Secondary prevention
“Action which halts the progress of a disease at
its incipient stage and prevents complications.”
“All measures available to reduce or limit
impairments and disabilities, minimize
suffering caused by existing departures from
good health and to promote the patient’s
adjustment to irremediable conditions.”

Modes of Intervention
1. Health promotion
2. Specific protection
3. Early diagnosis and treatment
4. Disability limitation
5. Rehabilitation

1. Healthpromotion
“The process of enabling people to increase
control over, and to improve health.” it is not
directed against any particular disease , but is
intended to strengthen the host through a variety
of approaches. The well-known interventions in
this area are:
i. Health education
ii. Environmental modifications
iii. Nutritional interventions
iv. Lifestyle and behavioral changes

Cont…
2. Specific protection
To avoid disease altogether is the ideal but this is possible
only in a limited number of cases. The following are
some of the currently available interventions aimed at
specific protection:
(a) Immunization
(b) Use of specific nutrients
(c) Chemoprophylaxis
(d) Protection against occupational hazards
(e) Protection against accidents

Cont…
(f) Protection from carcinogens
(g) Avoidance of allergens
(h)The control of specific hazards in the
general environment, e.g., air pollution,
noise control.

Cont..
3. Early diagnosis and treatment
A WHO Expert committee defined early detection
of health impairment as “the detection of
disturbances of homoeostatic and compensatory
mechanism while biochemical, morphological,
and functional changes are still reversible.”
4.Disability limitation
When a patient reports late in the pathogenesis
phase, the mode of intervention is disability
limitation.

Cont..
Concept of disability
Disease Impairment Disability Handicap
The WHO has defined these terms as follows:
(i) Impairment
(ii) Disability
(iii) Handicap

5. Rehabilitation
“The combined and coordinated use of medical, social,
educational and vocational measures for training and
retraining the individual to the highest possible level of
functional ability.”
The following areas of concern in rehabilitation have been
identified:
(a) Medical rehabilitation – restoration of function
(b) Vocational rehabilitation – restoration of the capacity to
earn a livelihood.
(c) Social rehabilitation – restoration of family and social
relationships
(d) Psychological rehabilitation – restoration of personal
dignity and confidence.

1
0
5
Definitions…
Epidemiology
and

Aims of epidemiology
According to the International Epidemiological Association
(IEA), epidemiology has three main aims
1. To describe the distribution and magnitude of health and
disease problems in human populations
2. To identify aetiological factors (risk factors) in the
pathogenesis of disease; and
3. To provide the data essential to the planning,
implementation and evaluation of services for the
prevention, control and treatment of disease and to the
setting up of priorities among those services.

The ultimate aim of epidemiology is to lead to
effective action :
• To eliminate or reduce the health problem or
its consequences; and
• To promote the health and well-being of
society as a whole

Measurements of epidemiology
1. Measurement of mortality
2. Measurement of morbidity
3. Measurement of disability
4. Measurement of natality
5. Measurement of the presence, absence or distribution of the
characteristic or attributes of the
disease
6. Measurement of medical needs, health care facilities, utilization of
health services and other health-related events
7. Measurement of the presence absence or distribution of the
environmental and other factors suspected of causing the disease,
and
8. Measurement of demographic variables.

Tools of measurement
• Rate
– Death, birth
• Ratio
– Sex ratio
– Doc:popu ratio
• Proportion
– %

Incidence
• No. Of new cases occuring in a defined
population during specified period of time
• Refers:
– Only new cases
– During given period of time
– In a risk population

Prevalence
• Refers to all current cases (old and new)
existing at a given point of time/ period in a
population
• 2 types
– Period
– Point

Definitions
1. INFECTION
The entry and development or multiplication of an infectious
agent in the body of man or animals (2,99). It also implies
that the body responds in some way to defend itself against
the invader, either in the form of an immune response
(evidence of this may not be readily available) or disease. An
infection does not always cause illness. There are several
levels of infection : colonization (e.g.,S. aureus in skin and
normal nasopharynx); subclinical or Inapparent infection
(e.g., polio); latent infection (e.g., virus of herpes simplex);
and manifest or clinical infection.
2. Contamination
The presence of an infectious agent on a body surface; also
on or in clothes, beddings, toys, surgical Instruments or
dressings, or other inanimate articles or substances including
of water, milk and food, Pollution is distinct from
contamination and implies the presence of offensive, but not
necessarily of infectious matter in the environment
Contamination on a body surface does not imply a carrier
state (99)
3. INFESTATION
For persons or animals the lodgement, development and
reproduction of arthropods on the surface of the body or in
the clothing, e.g., lice, itch mite (99). Some authorities use

DYNAMICS OF DISEASE
TRANSMISSION

1st - The Infectious Agent
3
-any disease-causing
microorganism
(pathogen)
Infectivity
Pathogenicity
Virulence

2nd: Source or Reservoir
• The starting point for the occurrence of a communicable
disease
Source of infection :•
• the person, animal, object or substance from which an
infectious agent passes or is disseminated to the host
(immediate source)
• RESERVOIR:
• “any person, animal, arthropod, plant, soil, or
substance, or a combination of these, in which
an infectious agent normally lives and multiplies,
on which it depends primarily for survival, and
where it reproduces itself in such a manner that
it can be transmitted to a susceptible host.
It is the natural habitat of the infectious agent.” 4

•5
Types of Reservoirs
Human
reservoir
Animal
reservoir
Non-living
reservoir

A person in the population or
study group
Identified as having
particular disease,health
disorder or condition
Underinvestigation
7

The clinical illness maybe mild or moderate,
typical or atypical, severe or fatal.
Epidemiologically, mild cases may be
more impor tant sources of
infection than severe cases because they
are ambulant and spread the infection
wherever they go, whereas severe cases
usually confined to bed.
8

Subclinical cases
Inapparent, Covert, Missed or Abortive Cases
• disease agent multiply in the host but does
not manifest by S/S.
• But contaminates the environment in the
same way as clinical cases.
• Subclinical cases play a dominant role in maintaining the
chain of infection in the community.
9

subclinical cases
detected only by
laboratory
tests
occurs in most
infectious disease.
Eg
 Rubella,
 Mumps,
 Polio,
 Hepatitis A and B,
 Influenza,
 Diphtheria
10

Latent infection
• The host doesnt shed the infectious agent
which lies dormant within the host without
symptoms

Latent infection
• infectious agent lies iinn aa nonon-n-iinfnfectectiioousus
ffoorm-rm-
ddormormantant within the host without
sysymmptptoommss with no shshededdidinngg (and often
without demonstrable presence in blood,
tissues or bodily secretions of the host)
egeg..
 HSV and VZV: nerve ganglia cells,
 CMV: kidney and salivary glands cells,
 EBV: lymphocytes
11

 Index Case
◦ Person that comes to the
attention of public health
authorities
 Primary Case
◦ First case of a communicable
disease introduced into the
population unit being studied
◦ Attack rate
 Secondary Case
◦ Person who acquiresthe disease
from an exposure to the primary
case
◦ Secondary attack rate
} Suspect case
Not diagnosed but have s/s
12

Carriers

13
An infected person or animal that harbours a
specific infectious agent in the absence of
disconcernible clinical disease and serves as a
potential source of infection for others
Reason :
due to inadequate treatment or immune respons
the disease agent is not completely eliminated
leading to a carrier state.

Three elements in a carrier state:
14

CARRIERS
• As a rule carriers are less infectious than
cases, but epidemiologically, they are more
dangerous than cases
• because
◦ escape recognition
◦ continuing to live a normal life among population
or community
◦ readily infect the susceptible individuals
◦ over a wider area and longer period of time under
favorable conditions.
◦ Classical eg. “Typhoid Mary”
15

IncuIncubatbatoorryy CCaarrrrieierrs:s: those who shed
the infectious agent during the incubation
period. This usually occurs during last few days
of IP
 Measles- the period of communicability is 4 days before the rash.
 Mumps- usually 4-6 days before onset of symptoms
 Polio- 7-10 days before onset of symptoms
 Hepatitis B- for a month before jaundice
 Pertusis
 Influenza
Classification of Carrier

Incubatory carrier
•Shed infec agent during incubation period
•Infect before onset of disease
•Usually occures during last few days of
incubaton period
•Eg. M, M, P, influ, D, Hep B

Carrier May Be
Classified :
ByType
Convalescent Carriers:
 those who continue to shed the disease agent during
the period of convalescence
 In the disease, clinical recovery does not
coincide with bacteriological recovery.
 Serious threat to HH members
 Highlights importance of bacteriological surveillance
of carriere state after recovery
◦ typhoid fever
◦ cholera,
◦ diphtheria,
◦ bacillary dysentery
◦ pertusis
17

Carrier may be
classified :
BY
TYPE
18
Healthy Carriers:
victims of subclinical infection who have
developed carrier state without suffering from
overt disease, but are nevertheless shedding the
disease agent
◦ poliomyelitis,
◦ cholera,
◦ meningococcal meningitis,
◦ salmonellosis,
◦ diphtheria.
Note:- Person whose infection remains subclinical may or may not act as
carrier (eg.- in polio inf may remain subclinical but person act as temp carrier
due to shedding of virus in stool..while TB most of us with +ve Mt, do not
disseminate bacillie- so not labelled as carrier.

Temporary carriers are those who shed the
infectious agent for short period of time.
Chronic carriers are those who excretes the
infectious agent for indefinite periods
19

Chronic carriers
Chronic carriers are far more important sources of
infection than cases.
The longer the carrier state, the greater the risk of
community-- reintroduce disease into areas which
are otherwise free of infection
The duration of the carrier state varies with the
disease.
 In typhoid fever and hepatitis B, the chronic
carrier state may last for several years.
 In chronic dysentery it may last for year or
longer.
 In diphtheria, the carrier state is associated with
infected tonsils, in typhoid fever with gall bladder
disease.
20

 Mary Mallon (1869 –1938), better
known as Typhoid Mary, was the
first person in the US identified as an
asymptomatic carrier of the
pathogen associated with
typhoid fever.


She was presumed to have
infected some 50 people, three of
whom died, over the course of her
career as a cook.
She was forcibly isolated twice by
public health authorities and died
after a total of nearly three
decades in isolation.
21

 Respiratory carrier: e.g.influenza
 Fecal (intestinal) carrier: e.g. typhoid,
choler
a
 Blood carrier: e.g. hepatitis B andHIV
 Urinary : e.g.Typhoid
 sexual Carrier: gonococcus and HIV
22
Carrier
classified :
By Portal Of Exit of Infectious Agent

Animal reservoirs
• infection that is transmissible under
natural conditions from animals to
man.
• e.g.
– Bacterial: Leptospira, plaguefrom Rat.
– Viral : Rabies from dog.
– Protozoa: Leishmaniasisfromdog.
– Helminths : Hydatiddiseasefromdog
– Tape worms: Cattle,Pig.
•23

Reservoir in non-living
things
Some organisms are able to
survive and multiply in
nonliving environments
such as soil and water
Clostridium that causes tetanus
and botulism can survive many
years in the soil
Hookworms deposit their eggs
into the soil
Water contaminated by human
or animal feces cause GI tract
disease (list includes bacteria,
viruses, protozoa)
•24

3rd - The Portal of Exit
25
• Route of escape of the pathogen from
the reservoir-IA entersintosurrounding
env-transfertohostattheirportalof entry
Examples:
respiratorysecretions,
GI
bloodexposure,
breaksin skin

4th –Mode of Transmission
26
Direct
transmission
Indirect
transmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
Vertical (transplacental)
Vehicle-borne
:Vector-borne
* m e c h a n i c a l
* b i o l o g i c a l
Air-borne *droplet
nuclei * dust
Fomite-born Unclean
hands and fingers

DirectContact
•Inf spread by direct contact of
skin-skin, skin mucosa, mucosa-
mucosa of same or other person
•by touching, kissing,,
bites, or sexual intercourse
•Direct & immediate transfer of IA
from reserviour –host (no intermediate
agency)
•So it introduces larger dose of IA
•No time interval of survival in
environment..
•Overcrowded place or where
place with lack of ventilation
•28
Scabies
Pediculosis
STD’s
Skin/eye inf
leprosy

Droplet spread:
•
• Direct projection of
droplets of
saliva/nasopharyngeal
secretion by
Sneezing, Speaking,
Coughing
Droplets directly
impinge on
conjunctiva, nasal
mucosa or skin
•29

•30
H1N1
Tubercle bacilli
Measles
•
•
•
• Chickenpox

• Inoculation:
Pathogen injected into tissues.
– Tetanus spores
– Arboviruses (Insects).
•31

Vertical transmission
Transplacental
 To R C H
 HIV
 HBV
•32
15

Indirect Transmission
5 ‘F’
33
food, flies, fomite, finger, fluid

Vehicle transmission
•
•
Water: Cholera, H A V , Typhoid
FOOD: Staphylococci,Cl. Botulinum.
Blood/serum- HIV, HBV,HCV
Organ-cmv
34

Trans-ovarian transmission
 Inf agentverticaltransmittedfromfemale
mosquitotoherprogeny
◦ Scrub typhus
◦ Rickettsialpox
◦ Indianticktyphus
◦ Q fever
◦ RMSF
Trans-stadial transmission-
Lymedisease,infectstickvectorasalarva,andthe
infectionismaintainedwhenitmoltstoanymphand
laterdevelopsasanadult
36

 host feeding preference
 infectivity-ability to transmit disease agent
 susceptibility –ability to becomeinfected
 survival rate of vectors in environment
 Domesticity
 Seasonal factors…
37

Fomites:
Contaminated Nonliving Objects likeCup, towel,
napkin, linen, Clothing,glass, Toys,Pencils,doorhandle,
surgicalinstruments,syringes,dressingmaterials…
Ex: Diphtheria,
Trachoma
influenza
scabies
38

5th - The Portal of Entry
•39
-route through which the
pathogen enters its new
host

Respiratory System
•40
Upper respiratory tract
Diphtheria
Lower respiratory tract
Tuberculosis

Gastrointestinal System
ingestion
Feco-Oral Route
Infectious agent excreted in faeces
& transmitted to the oral
portal of entry through
contaminated food, water, milk,
drinks
hands
• Typhoid fever
• Shigella
• Cholera
• Polio
• Rotavirus
• Hepatitis A, Hepatitis E
•41

Urinary & Reproductive
Tracts
•42
Gonorrhea
Syphilis
HIV

Breaks in Protective Skin
Barrier
•43
Percutaneous
Leptospirosis
Percutaneous
(bite of arthropod)
Yellow fever

6th - The Susceptible Host
44
• A person or an animal that afford lodgment
to an infectious agent under natural
conditions.
•Accepts the pathogen
•The support of pathogen life & its
reproduction depend on the degree of the
host’s resistance.

•Cancer Patients
•HIV-AIDS Patients
•Transplant
Patients
•On steroids..
•Infant & Elderly
Patients 45

HOST
Obligate host : the only host
Eg: Man in measles & typhoid
Primary /definitive host: in which
parasite attains maturity or passes
its sexual stage
Secondary or intermediate hosts:
the parasite is in a larval or asexual
state
•46

Life cycle
Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male / Female
MosquitoZygote
Ookinete
Oocyte
Salivary
Gland
Exflagellation

THE TIME INTERVAL BETWEEN INVASION BY
AN INFECTIOUS AGENT ANDAPPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE
DISEASE IN QUESTION
Incubation Period

DOSE OF INOCULUM
SITE OF MULTIFICATION
RATE OF MULTIFICATION
HOST DEFENCE MECHANISM
Incubation Period

Period From Disease Initiation To
Disease Detection

THE GAP IN TIME BETWEEN
THE ONSET OF THE
PRIMARY CASE AND THE
SECONDARY CASE

It is defined as the time during which
an infectious agent may be transferred
directly or indirectly from an infected
person to another person, from an
infected animal to man , or from an
infected person to an animal, including
arthropods

Ate the food (exposed) Did not eat the food (not exposed)
Ill Well Total Attack
Rate
Ill Well Total Attack
Rate
10 3 13 76% 7 4 11 64%
Attack Rate = Ill / (Ill + Well) x 100 during a time period
Attack rate = (10/13) x 100 = 76%
( 7/11) x 100 = 64%

It is defined as the number of exposed
persons developing the disease within the
range of the incubation period, following
exposure to the primary case

 Used to estimate to the spread of disease in a
family, household or other group environment.
 Measures the infectivity of the agent and the
effects of prophylactic agents (e.g. vaccine)
58
SAR (%)
Totalnumberof cases– initialcase(s)
Numberof susceptiblepersonsinthegroup–
initialcase(s)
= x100

Disease -Prevention
Activities designed to protect patients and
other members of the public from actual or
potential health threats and their harmful
consequences.
from: Mosby’s Medical Dictionary,8th
edition2009.

Levels of Prevention
4 levels
1. Primordialprevention
2. Primaryprevention
3. Secondaryprevention

PrimordialPrevention
 Prevention of emergence or development of risk factors in countries or
population groups in which they have not yet appeared.
 INTERVENTION: Individual and mass education.
EXAMPLES: National programmes and policies on
Food and nutrition
Against smoking and drugs
To promote regular physical exercise
PrimaryPrevention
• Action taken prior to onset of disease, which removes the possibility that
a disease will ever occur.
• INTERVENTION:Prepathogenesis stage of disease.
• MODESOFINTERVENTION:Health promotion and Specific protection

SecondaryPrevention
 Action which halts the progress of the disease at its incipient stage and
prevents complication.
 INTERVENTION: Early pathogenesis stage
 MODESOFINTERVENTION:Early diagnosis and Adequate/prompt
treatment.
TertiaryPrevention
• All measures available to reduce or limit impairments and disabilities
and minimize suffering caused by existing departures from good health
and to promote the patients adjustment to irremediable conditions.
• INTERVENTION: Late pathogenesis stage
• MODESOFINTERVENTION:Disability limitations and Rehabilitation

Disease -Control
 Disease control is reducing the transmission of disease
agent a low level that it ceases to be a public health
problem.
 It describes operations aimed at reducing-
1. The incidence of disease.
2. The duration of disease, and consequently the riskof
transmission.
3. The effects of infection, including both the physical and
psychosocialcomplications.
4. The financial burden of thecommunity.

 Controlling the reservoir
1. Early diagnosis
2. Notification
3. Epidemiological investigations
4. Isolation
5. Quarantine
 Interruption oftransmission
 The susceptiblehost
1. Active immunization
2. Passive immunization
3. Combined passive and active immunization
4. Chemoprophylaxis
5. Non specific measures
Disease control involves-

Early diagnosis
Needed for-
1. Treatment of patient
2. Epidemiological investigation for ex to trace the
source of infection from the known or index case to
the unknown.
3. To study the time, place and person distribution.
4. For the institution of prevention and control
measures.

Notification
 Once a infectious disease has been detected or
suspected is should be notified to local health
authority.
 Disease under surveillancebyWHO
5 relapsing fever
6 malaria
1. Louse borne-typhusfever
2. Paralytic polio
3. Viral influenza A
7 SARS
4. small pox
 Disease under International Health Regulation(IHR)-
Cholera, Plague and Yellow fever.

Epidemiological Investigation
 The outbreak investigation helps to identify-
1. The source of infection
2. Factors influencing the Spread.
 These may include
1. Geographical situations
2. climatic condition, social and behavioral patterns
3. The character of the agent , reservoir, the vector and
vehicles and susceptible host population.

Isolation
 Separationfortheperiodofcommunicabilityofinfected
personsoranimalsfromothersinsuchplacesandunder
suchconditions,astopreventorlimitthedirectorindirect
transmissionoftheinfectiousagentfrominfectedto
susceptible.
 The duration of isolation depends on duration of
communicability of disease and effect of chemotherapy on
infectivity .
 E.g. chicken pox until all lesions
crusted ,usually about 6 days after
onset of rash.

Treatment
 The objectives of treatment are-
1. To kill the infectious agent when it is still in the
reservoir before it is disseminated.
2. Reduce the communicability of disease.
3. Cut short the duration of illness and
4. Prevent development of secondary cases

Quarantine
 Defined as “ the limitation of freedom of movement of such
well person or domestic animal exposed to communicable
disease for a period of time not longer than the longest
usual incubation period of disease in such manner as to
effective contact with thosenot so exposed”
 3 types-
Absolute
Modified
Segregation

Interruption of transmission
 Means changing some components of man’s environment
to prevent the infective agent from a patient or carrier
from entering the body of susceptible person.
 E.g. simple chlorination to complex water
treatment will prevent water borne disease.
 Vector control.
 Personal hygiene.

Active & PassiveImmunization
 Active - strengthening of host defence ; control of some
infectious disease is solely based on active immunization-
e.g. polio , tetanus, diphtheria and
measles.
 Passive – 3 types of preparations are available
1. Normal human Ig
2. Specific (hyperimmune) human immunoglobulin
3. Antisera or antitoxin

Chemoprophylaxis
 Implies the protection from, or prevention of,
disease.
 Achieved by –
1. Causal prophylaxis-early elimination of
invading or migrating causal agent.
2. Clinical prophylaxis- prevention of clincal
symptom.

Non specific measures
 Mainly interrupt pathways of transmission.
 Improvements on the Quality of Life (eg better
housing, water supply, nutrition,education)
 Formulation of legislative measures and
integrated program.
 Have played a dominant role in decline of
diseases like TB, Cholera, Leprosy and Child
Mortality.

Surveillance
 SURVEILLANCE must follow control measures.
Defined as “ the continuous scrutiny of allaspects
of occurrence and spread of disease that are
pertinent to effective control.”
 The ultimate objective of surveillance is
“PREVENTION”.

Types ofsurveillance
 4 types
1. Individual surveillance- surveillance of infected person
until they are no longer a significant risk to other
individual..
2. Local population surveillance- surveillance of malaria.
3. National population surveillance- surveillance of small
pox after it has been eradicated.
4. International surveillance- WHO maintains surveillance
of important diseases like influenza, malaria ,polio.

 The objectives of an epidemic investigation are
a. To define the magnitude of the epidemic or outbreak
involvement in terms of time, place and person.
b. To determine particular conditions and factors responsible
for the occurrence of the epidemic.
c. To identify the causative agent, sources of infection, and
modes of transmission.
d. To make recommendations to prevent recurrence

1. Verification of diagnosis
2. Confirmation of the existence of an epidemic
3. Defining the population at risk
4. Rapid search for all cases and their characteristics
5. Data analysis
6. Formulation of hypothesis
7. Testing of hypothesis
8. Evaluation of ecological factors
9. Further investigation of population at risk
10. Writing the report

 First step in the investigation.
 The report may be spurious due to misinterpretation of signs
or symptoms by public or health worker.
 It is not necessary to examine all the cases.
 A clinical examination of a sample of cases is sufficient.
 Laboratory investigations wherever applicable, are most
useful to confirm the diagnosis but control measures should
not be delayed until laboratory results are available.

 Done by comparing the number of cases with disease frequencies
during the same period of previous years.
 In case of endemic diseases like cholera, typhoid hepatitis A, it is
expected that some cases (few hundreds) always present throughout
the year. So these diseases to be consider as epidemic several
hundreds or thousands of cases have to occur in India.

 In case of yellow fever, bubonic plague and polio even a
single case will constitute an epidemic in India.
 But in the US single case of cholera constitute epidemic.
 Thus the number that constitute an epidemic vary from
place to place.

1. Obtaining the map of the area
 It should contain information about natural landmarks, roads and
location of all dwelling units along each road.
 The area may be divided into segments, using natural landmarks as
boundaries.
 This is again divided into smaller sections. Within each section, the
dwelling units may be designated by numbers.

2. Counting the population
 By doing census by house to house visits. The composition should be
known by age and sex.
 Eg: For population at risk. In case of food poisoning- those who ate
the food. In case of outbreak of cholera- those who were using
water from the suspected well.

Surveillance:
It has been defined as "the continuous scrutiny of all aspects of
occurrence and spread of disease that are pertinent to effective
control“.
 The ultimate objective of surveillance is prevention.
 Surveillance, if properly pursued, can provide the health agencies
with an overall intelligence and disease-accounting capability.
 Surveillance is an essential prerequisite to the rational design and
evaluation of any disease control programme.

 (a) Individual surveillance : This is surveillance of infected persons
until they are no longer a significant risk to other individuals,
 (b) Local population surveillance : e.g., surveillance of malaria,
 (c) National population surveillance : e.g., surveillance of smallpox
after the disease has been eradicated,
 (d) International surveillance : At the international level, the WHO
maintains surveillance of important diseases (e.g., influenza,
malaria, polio, etc.) and gives timely warning to all national
governments.

It has to be done using the parameters – Time, Place And Person.
a. Time
Prepare a chronological distribution of dates of onset of cases
and construct an “epidemic curve”. An epidemic curve
suggests :
Pattern of spread
Magnitude
Outliers
Exposure and/or disease incubation period

10
5
0
15
Time
1
Median onset time
3
Probable exposure time 50% 50%
Median incubation time
2
1 2 3 4 5 6 7 8 9 10 11 12 1314 15 16 17 18 19 20 21 22
No of cases

b. Place
 Prepare a ‘spot map’ of cases and if possible their relation to
the sources of infection e.g. water supply, air pollution,
foods eaten, occupation etc..
 The map shows the boundaries and patterns of disease
distribution. Clustering of cases indicate a common
source of infection.
39

Original map by Dr. John Snow showing the clusters of Cholera cases
in the London epidemic of 1854
40

c. Person
 Analyze the data by age, sex, occupation and other possible risk
factors.
 Determine the attack rates/case fatality rates.
The purpose of data analysis is
1. To determine modes of transmission and the source and the vehicle
of the agent, so that the most effective measures can be initiated.
2. To determine the risk factors for disease.
41

 Hypothesis is a proposition or a tentative theory designed to explain
the observed distribution of the disease in terms of causal
association of the direct nature.
 The hypothesis should explain the epidemic in terms of
1. Causative agent
2. The possible source
3. Possible modes of spread
4. The environmental factors which enabled
it to occur.
42

 All reasonable hypotheses need to be considered and weighed by
comparing the attack rates in various groups for those exposed and
those not exposed to the each suspected factor.
 This will enable the epidemiologist to ascertain which hypotheses is
consistent with all the known facts.
 Sometimes the hypothesis needed to be tested by the analytical study
design (case control study) to the statistical significance.
43

 An investigation of the circumstances involved should be carried out
to undertake appropriate measures to prevent further transmission
of the disease.
 The ecological factors which have made the epidemic possible should
be investigated such as sanitary status of eating establishments,
breakdown in the water supply system, changes such as temperature,
humidity, and air pollution, population dynamics of insects and animal
reservoirs etc..
 In case of water-borne transmission is suspected(gastroenteitis) a
sanitary survey of water supply system from source to consumer
should be done. 44

 Needed to obtain further information.
 This may involve medical examination, screening tests,
examination of suspected food, feces or food samples,
biochemical studies, assessment of immunity status etc.
 This will permit classification of all members as to
1. Exposure to specific potential vehicles
2. Whether ill or not
45

1. Background
 Geographical location
 Climatic conditions
 Demographic status (population pyramid)
 Socioeconomic situation
 Organization of health services
 Surveillance and early warning systems
 Normal disease prevalence

2. Historical data
 Previous occurrence of epidemics
- of the same disease
- locally or elsewhere
 Occurrence of similar diseases
- in the same area
- in other areas
 Discovery of the first cases of the present outbreak

3. Methodology of investigations
 Case definition
 Questionnaire used in epidemiological investigation
 Survey teams
 Household survey
 Collection of laboratory specimens
 Laboratory techniques

4. Analysis of data
 Clinical data
- frequency of signs and symptoms
- course of disease
- differential diagnosis
- sequelae or death rates
 Epidemiological data
- Mode of occurrence
- In time
- By place
- By population groups

 Modes of transmission
- sources of infection
- routes of excretion and portal of entry
- factors influencing transmission
 Laboratory data
- isolation of agents
- serological confirmation
- significance of results
 Interpretation of data
- comprehensive picture of the outbreak
- hypothesis as to the causes
- formulation and testing of hypothesis by statistical analysis

5. Control measures
ogy of
 Definition of the strategies and
methodol implementation
- constraints
- results
•  Evaluation
- significance of results
- cost/effectiveness
•  Preventive measures

temporary control measures at the
commencement of an epidemic on
the basis of known facts of the
disease.
 These measures may be modified or
replaced in the light of new
knowledge acquired by the epidemic

Health disease and epidemiology

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