UNIT: 15

EPIDEMIOLOGY
Sushila Pokharel
Lecturer
Community Health Nursing
 CONTENT(12 hours)
Commonly used term in epidemiology
Aim and uses of epidemiology
Epidemiological approach
◦ Asking question
◦ Making comparison
The concept of disease causation
◦ Agent
◦ Host
◦ Environment
Dynamics of disease transmission
◦ Sources of disease transmission
◦ Modes of transmission
◦ Susceptible host
 Level of disease prevention and modes of intervention
◦ Primordial prevention
◦ Primary prevention
 Health promotion
 Specific protection
◦ Secondary prevention
 Early diagnosis and treatment
 Disability limitation
◦ Tertiary prevention
 Rehabilitation
 Disease prevention and control
◦ Controlling the reservoir
◦ The interruption of transmission
◦ The susceptible host
 Introduction
Epidemiology is derived from the Greek word
Epi=upon ， among, Demos=people, Logos=
science, study, knowledge.
EPI DEMOS LOGOS
Upon, People, population, man the Study of

The study of anything that happens to

people
“Study among the population”
 Epidemiology is the study of the distribution and
determinant of health related states or events in
specified population and the application of this study
to the control of health problems. John M, Last, 1988

 Epidemiology is the study of distribution and

determinate of disease frequency in man. Mac
Mohan, 1960
Centre for diseases control, US public Health
Service has defined epidemiology as the
study of the patterns of diseases and the
factors that causes disease in man.
 Distribution refers to the frequency of occurrence of states
of health and illness .

 Determinants refer to the etiological or risk factors related

to particular disease.

 Events refer to all the conditions of the spectrum of health

such as disease, injury, disability and death.
Commonly used term in epidemiology
Infection
 The entry and development or multiplication of an infectious
agent in the body of a host (man or an animal) is known as
infection. An infection does not always cause illness.

 Infection is the successful entry, invasion (attack),

establishment and development or a multiplication of a disease
producing agent in the tissues of the host.
The invasion and multiplication of
microorganism such as bacteria, viruses and
parasites that are not normally present within
the body is known as infection.
Contamination
The presence of an infectious agent on a body
surface; also on or in clothes, bedding, toys,
surgical instruments or dressing or other
inorganic articles or substance including
water, food, and milk is contaminate.
Communicable disease

An illness due to a specific infectious agent or its

toxic products capable of being directly or indirectly

transmitted from an infected man or animal or a

reservoir to susceptible host is called communicable

disease. E.g TB, dysentery, cholera etc.

Non communicable disease
Diseases which are not transmitted from one
person to another, an animal to person is called
non communicable diseases. E.g heart disease,
diabetes.
Contagious Disease:
A disease that is transmitted through contact. E.g. STI,
Scabies
 An infectious disease (such as influenza, measles, or
tuberculosis) that is transmitted by contact with an infected
individual or infected bodily discharges or fluids (such as
respiratory droplets), by contact with a contaminated surface
or object, or by ingestion of contaminated food or water.
Epidemic
 If a disease from a specific source spreads quickly and
attacks a large number of people in an area, it is called
an epidemic disease. For e.g measles, chicken pox and
cholera, influenza etc. The unusual occurrence in a
community or region of disease, specific health related
behavior e.g. smoking or other health related events
e.g. traffic accident, clearly in excess of expected
occurrence.
Endemic

Endemic means the constant presence of

disease or infectious agent within a given

geographic area or population group, without

importation from outside may also refer to

usual or expected frequency of the disease

within such area or population group.

Certain diseases which continuously appear to a
greater or lesser extent in specific region are
called endemic disease for those areas. E.g.
malaria in Terai, common cold in hilly region.
Endemic disease can become epidemic if not
controlled or when conditions are favorable.
Pandemic
A disease is said to be pandemic when it
spreads from one country to another in a
short time or occurs at the same time in
different countries. E.g influenza cholera,
HIV, AIDS, bird flu, covid
Sporadic
 The word sporadic means scattered about. The cases occur
irregularly, haphazardly from time to time and generally
infrequently.
 The cases are so few and separated widely in space and the
time that they show little or no connection with neither each
other nor a recognizable common source of infection. E.g
polio, tetanus, herpes zoster, etc. A sporadic disease may be
the starting point of an epidemic when conditions are
favorable for its spread.
Eradication
 Eradication is the reduction of infectious diseases
prevalence in the global host population to zero.
Eradication is an absolute process an ‘all or none’
phenomenon restricted to termination of an infection
from the whole world. It implies that disease will no
longer occur in a population. Eradication means tear
out the disease from root. E.g. small pox
Surveillance
 The continuous study of the factors that determine
the occurrence and distribution of a disease and
other condition of ill health is surveillance.
Surveillance is essential for effective control and
treatment of disease and it includes the collection,
analysis, interpretation and distribution of relevant
data for action.
Incubation period

This is the time interval between invasion (entry) of

an infectious agent into the body and manifestation

(appearance) of the 1st sign or symptoms of the

disease is known as incubation period. During the

incubation period the infectious agent undergoes

multiplication in the host.

Carrier

 An infected person or an animal that harbors a specific

disease causing agent, in the absence of clinical

manifestation and serves as potential sources of

infection to others is a carrier. In another word a carrier

outwardly looks healthy, but can infect others.

Fomites
 Fomites are inorganic articles or substance other than
water or food contaminated by the infectious discharges
from patient and capable of harboring and transferring
the infectious agent to a healthy person. E.g soiled
clothes, towels, linen, handkerchief, cups, spoon, etc. The
fomites play an important role in indirect infection.
Diseases transmitted by fomites include diphtheria,
typhoid fever, hepatitis, eye and skin infection etc.
Disinfection
Disinfection is the killing of infectious agent
outside body by direct exposure to chemical or
physical agents. The agent used for
disinfection is known as disinfectants.
Disinfection destroys the pathogenic organism
of equipments, fomites, surfaces, excreta.
Isolation
 Isolation means the separation of infected person or animals
for a period of communicability to prevent or limit direct or
indirect transmission of the infectious agent is called
isolation.
 This helps to control the spread of epidemic disease. In
isolation the patients is kept away separately and all the
things used by him/her are disinfected, all the medical
personnel take universal precaution while giving care and
carrying out treatment.
Zoonosis
An infection or infectious disease transmitted from
vertebrate animal to man under natural condition is
Zoonosis. E.g. rabies, plague, bovine TB etc.
Nosocomial infection
 Nosocomial (hospital acquired) infection is an infection
originating in a patient while in a hospital or other health care
facility. It denotes a new disorder (unrelated to patient’s
primary conditions) associated with being in a hospital. It
was not present or incubated at the time of admission but
appearing after discharge due to acquired from hospital e.g.
surgical wound infection, hepatitis B, UTI etc.
Infection originating in a patient while in a
hospital or another health care facility. It has to be a
new disorder unrelated to the patient’s primary
condition. Examples include infection of surgical
wounds, hepatitis B and urinary tract infections.
Quarantine:
Restriction of the activities of well persons or
animals who have been exposed to a case of
communicable disease during its period of
communicability (i.e. contacts) to prevent disease
transmission during the incubation period if infection
should occur.
Opportunistic infection
This is infection by an organism that takes the
opportunity provided by a defect in host
defense(immunity) to infect the host and hence
cause disease. For example opportunistic
infection is very common in AIDS.
Susceptible host( lacking immunity or resistance
power)
If a person lack capacity to fight certain disease that
person is considered to be susceptible to that disease.
Example malnourished children are susceptible to
many diseases because they lack the power to fight
against diseases.
Infestation
The lodgment, development and
reproduction of arthropods on the surface of
the body or in clothing are called infestation
e.g. lice, worms
Resistance
Some people can fight against diseases. This capacity
of fighting against disease is called resistance.

Exotic
Describing a disease occurring in a region of the
world far from where it might be expected. Thus
malaria is regarded as exotic when it is diagnosed in
patients in Britain
Epizootic
 An epidemic outbreak of disease affecting many
animals of one kind at the same time.

Enzootic
 Prevalent among or restricted to animals of a
specific geographic area. Constantly present in a
locality.
Infectivity:
 Ability of microorganism to invade and multiply in the
host.

Pathogenicity:
 Ability to produce illness or disease.
 Ability of a microbe to cause disease or damage to its host.
Virulence:
Ability to produce severity and fatality.
Proportion of clinical cases resulting in severe
clinical manifestation.
The severity of the damage each microbe can cause
is referred to as its virulence.
Elimination:
Interruption of transmission of disease.
Reduction to zero of the incidence of infection
caused by a specific agent in a defined geographical
area as a result of deliberate efforts; continued
measures to prevent re-establishment of transmission
are required.
E.g. measles, poliomyelitis.
 Aims of epidemiology
 To describe the distribution and magnitude of health and
disease problems in human population.
 To identify etiological factors(risk factors) in the
pathogenesis of disease.
 To provide the data essential in the planning,
implementation and evaluation of services for the
prevention, control and treatment of disease and the
setting up 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.
 To promote the health and well being of the
society as a whole.
 Uses of epidemiology
 To study the effects of disease state in a population
over a time and predict future health needs.
 To diagnose the health of the community.
 To evaluate health services.
 To estimate the individual risk from group
experiences.
To identify the syndrome.
To search for the causes of health and
disease.
 Scope of epidemiology
 Historically epidemiology was concerned with
infectious disease and epidemic disease.
 It has expanded greatly in scope and the
definition of epidemic, now it is concerned with
non infectious disease including infectious
disease like coronary disease, diabetes,
accidents, cancer and mental illness.
Modern epidemiology has focused all disease
whether acute or chronic, physical or mental,
communicable or non communicable. Now it is
concerned with the systematic study of:
Whole population in their living and working
environment.
Factor that determine a state of health and
disease.
Pattern of health and illness.
Multiple factor of causation
Measure of prevention and control.
Concept of disease causation
DISEASE
A condition in which body’s health is impaired, a
departure from a state of health, an alternation of
the human body interrupting the performance of
vital functions.

Webster Dictionary
• A condition of the body or some part or organ of
the body in which its function are disrupted or de
arranged.
Oxford English Dictionary
 From the ecological point of view disease is
define as maladjustment of the human organism
to the environment.
The simplest definition is disease is just the
opposite of health i.e. any deviation from
normal functioning or state of complete
physical or mental well being since health
and disease are mutually exclusive.
 Concept of disease causation
Primitive theory
Sickness as a punishment sent by the gods
for breach of religious prohibitions or social
prohibitions having divine sanction.
Disease is due to the presence of evil, spirits,
ghosts, or demons in the body .
 Germ theory
 Several theories were advanced from time to time to
explain disease causation like supernatural theory,
spontaneous theory and other.
 The breakthrough came in 1860, when the French
bacteriologist Louis Pasteur (1822-1895)demonstrated
the presence of bacteria in air.
 He disproved the theory of “spontaneous generation”.
In 1873, Pasteur advanced the “germ theory of
disease”.
 In 1877, Robert Koch(1843-1910) showed that anthrax was
caused by a bacteria.
 The discoveries of Pasteur and Koch. confirmed the germ
theory of disease.
 The theory which explain most infectious disease are caused
by the germs is known as the germ theory of disease.
 All attention was focused on microbes and their role in
disease causation. The germ theory of disease came to the
forefront.
 The germ theory of disease gained momentum
during the 19th and the early part of 20th century.
 Germ theory states that many diseases are
caused by the presence and actions of specific
micro-organisms within the body.
 The emphasis had shifted from empirical causes
(e.g., bad air) to microbes as the sole cause of
disease.
 The concept of cause embodied in the germ
theory of disease is generally referred to as a one-
to-one relationship between causal agent and
disease. The disease model accordingly is:
 Disease agent Man Disease
 The germ theory of disease, though it was a
revolutionary concept, led many epidemiologists
to take one-sided view of disease causation
That is, they could not think beyond the germ
theory of disease. It is now recognized that a
disease is rarely caused by a single agent alone,
but rather depends upon a number of factors
which contribute to its occurrence. Therefore,
modern medicine has moved away from the
strict adherence to the germ theory of disease.
 Epidemiological Triad
It is a broad concept of disease causation. The
concept resulted due to limitations of germs theory of
disease.
According to this concept, disease occur when the
equilibrium between agent host and environment is
disturbed.
The interaction between the agent, host and
environment is known as epidemiological triad.
In this model, disease results from the
interaction between the agent and the
susceptible host in an environment that
supports transmission of the agent from a
source to that host.
The mere presence of agent, host and favorable
environmental factors in the pre pathogenesis period
is not sufficient to start the disease in man. What is
required is an interaction between 3 factors to initiate
the disease process in man.
Epidemiological Triad
 Agent factor
 Agents of infectious diseases include bacteria, viruses,
parasites, fungi, and molds.

 With regard to non-infectious disease, disability, injury or

death, agents can include chemicals from dietary foods,
tobacco smoke, radiation or heat, nutritional deficiencies, or
other substances, such as poison.

 One or several agents may contribute to an illness.

 It is defined as a substance living or non living tangible
or intangible the excessive presence or relative lack of
which may initiate immediate cause of a particular
disease.

A disease may have a single agent, a number of

independent alternative agents or a complex of two or
more factors whose combined presence is essential for
the development of the disease.
Disease agent may be classified as:
Biological agents
Nutrient agents
Physical agents
Chemical agents
Mechanical agents
Social agent
Absence or excess of a factor necessary to health
1. Biological agents
 It includes all living organisms as bacteria, virus, fungi,
protozoa, helminthes.
 But all biological agents are not infectious, there should
be favorable environment. Certain micro-organisms are
normal flora (bacteria present in our body which does
not cause disease) for a certain area.
 For disease to be produced, a biological agents should
have following features:
(i) Infectivity: this is the ability of an infectious agent
to invade and multiply (produce infection) in a
host;

(ii) Pathogenicity: this is the ability to induce

clinically apparent illness, and

(iii) Virulence: this is defined as the ability to produce

severity and fatality.
2. Nutrient agents
 The nutrient needed for our body is protein, fat,
carbohydrates, vitamin, minerals, and water. An
excess or deficiency of the intake of nutritive
elements may result in nutritional disorders.
Protein energy malnutrition, anemia, goiter,
obesity and vitamin deficiencies.
3. Physical agents
It includes exposure to excessive heat, cold,
humidity, pressure, radiation, electricity,
sound etc. and may result in illness. E.g
burns, heatstroke, frostbite, etc.
4. Chemical agents
 Endogenous: some of chemicals produced in the
body as a result of rearrangements of function as
urea (uremia), serum bilirubin (jaundice), uric acid
(gout), calcium carbonate (kidney stone) etc.
 Exogenous: agents arising outside of human host as
allergens, metal, fumes, gases, insecticides etc. these
may be acquired by inhalation, ingestion or
inoculation.
5. Mechanical agents
Exposure to chronic friction and other
mechanical force resulting in injuries, trauma,
fracture, sprains, dislocations and even death.
6. Absence or insufficiency or excess of a factor
necessary to health

• Excess or lack of hormones, nutrients etc can leads to

variety of diseases.
7. Social agents
 These are poverty, smoking, drug abuse, unhealthy
lifestyle, alcoholism, social crime, maternal
deprivation, social isolation etc.

 Thus, the word agent has very broad concept. It

includes both living and non living agent. In
epidemiological terminology, the disease agent is
referred to as seed.
 Host
 Host refers to human or animal that comes in contact with
the agent. In epidemiologic concept, the host is considered
as soil and the disease agent as a seed.
A host offers subsistence and lodging for a pathogen and
may or may not develop the disease.
 The level of immunity, genetic makeup, level of exposure,
state of health, and overall fitness of the host can
determine the effect a disease organism will have on it.
 The makeup of the host and the ability of the pathogen

to accept the new environment can also be a determining

factor because some pathogens thrive only under limited

ideal conditions.

 The occurrence of disease in man depends upon certain

inherent factor in the human host. These host factors are

as:

 Demographic characteristics such as age, sex, race,

ethnicity etc.
 Biological characteristics such as genetic factors, biochemical
level of blood, blood group, enzyme, immunological factors,
and physiological functions of body organ.

 Socio economic characteristics such as socio economic status,

education, occupation, marital status, housing, stress factor
etc.

 Lifestyle factors such as personality, living habits, nutrition,

physical exercise, use of alcohol, drugs and smoking etc.
Age
 Certain diseases are more frequent in certain age groups than
others e.g. measles, whooping cough in children, diabetes,
hypertension in adulthood, cardiovascular disease in old age.

Sex
 Certain diseases are concentrated in certain sex groups due to
an anatomical and hormonal difference e.g. hemophilia and
BEP in male, gynecological and obstetric related problems in
female.
Race
Some race also suffers from particular diseases
e.g. Negros suffer from sickle cell anemia.

Genetic factors
Certain diseases are determined by genetic
factors, chromosomal abnormalities, blood
disorders etc.
Habits/nutrition
 Lifestyle such as dietary patterns, use of tobacco,
alcohol, narcotic drugs are the factors which cause
susceptibility to disease e.g. malnutrition, cancer, drug
abuse. There are also diseases associated with over eating
e.g. obesity. Habits like open field defecation favor
transmission of diarrheal diseases, worm infestation.
Lack of physical exercise predisposes to heart diseases.
Occupation
 The occupation of the host may predispose him/her to certain
occupational diseases like lead poisoning, accidents.

Immunity
 The reaction of human host to infection depends upon his/her
previous immunological status e.g. infection, immunization.
Individual having natural or acquired immunity are not easily
susceptible to diseases.
Socio-economic status
 Lower socio economic status are susceptible to bronchitis,
TB other communicable and infectious diseases. Higher
social classes have chronic and genetic diseases.

Educational status
 Diseases can be easily managed and controlled in the
educated family and difficult to manage in uneducated
family.
 Environment
 The disease agents are found in the environment e.g.
water, air, soil, insects, rodents.

 The environment has been divided into three components.

They are closely related to each other and with host factor.

 There are three components of environment. They are

physical, biological and psychosocial.
Physical environment
 It includes non living things and physical factor such
as water, air, soil, heat, light, radiation, noise,
housing, climate, geography etc. alteration in their
environment due to various areas leads to pollution as
water pollution, air pollution, noise pollution, soil
pollution which cause disease e.g. heavy flooding in
village causes water contamination that lead to the
epidemic of water borne diseases.
Biological environment
It includes all living things created in the
world, man lives around the living things
which include bacteria, virus, and other various
micro organisms which may cause disease and
maladjustment in the ecological system leading
to causative factors of disease.
Psychosocial environment
 Man has to live in society and should follow the accepted
patterns of particular society such as culture, values,
morals, customs, habits, attitudes, religion, and other
psycho societal factor.
 Any alteration in these factors may lead to conflicts and
tensions which may causes behavioral disorders. The habit
like smoking, alcoholism, drug abuse is problem to psycho
social disturbance.
Multi-factorial causation
 The concept of multi-factorial causation or multiple cause
theory explains that disease occur due to multiple factor. The
concept that disease is due to multiple factors is not a new
one.
 Pettenkofer of Munich (1819-1901) was an early proponent
of this concept.
 Although this concept was developed in 19th century, the
development of “germ-theory of disease” or “single cause
idea” in the late 19th century over-shadowed the multiple
cause theory.
 As a result of advances in public health, chemotherapy,
antibiotics and vector control, communicable diseases
began to decline – only to be replaced by new types of
diseases, the so-called “modern” diseases of civilization.
E.g., Lung cancer, coronary heart disease, chronic
bronchitis, mental illness, etc.
 These diseases could not be explained on the basis of the
germ theory of disease nor could they be prevented by the
traditional methods of isolation, immunization or
improvements in sanitation.
The realization began to dawn that the
“single cause idea” was an
oversimplification and that there are other
factors in the aetiology of diseases –
social, economic, cultural, genetic and
psychological which are equally
important.
 It is now known that diseases such as coronary heart disease
and cancer are due to multiple factors. For example, excess
of fat intake, smoking, lack of physical exercise and obesity
are all involved in the pathogenesis of coronary heart
disease. Most of these factors are linked to lifestyle and
human behavior.
 Medical men are looking “beyond the germ theory of
disease into the total life situation of the patient and the
community in search of multiple (or risk) factors of disease.
Behavior, lifestyle factors, environmental
causes, ecologic elements, physical factors, and
chronic diseases must also be taken into account.
The term agent is replaced by causative factors,
which implies the need to identify multiple
causes or aetiologic factors of disease, disability,
injury and death.
The purpose of knowing the multiple factors
of disease is to quantify and arrange them in
priority sequence (prioritization) for
modification or for making improvement to
prevent or control disease. The multifactorial
concept offers multiple approaches for the
prevention/control of disease.
Web of causation
 This model of disease causation was suggested by
MacMohan and Pugh in their book:
“Epidemiologic Principles and Methods”.
 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 interrelationship
with each other.
 The basic tenet(principle) of epidemiology is to study
the clusters of causes and combinations of effects
and how they relate to each other. It can be
visualized that the causal web provides a model which
shows a variety of possible interventions that could be
taken which might reduce the occurrence of disease.
 The web of causation does not imply that the disease
cannot be controlled unless all the multiple causes or
chains of causation or at least a number of them are
appropriately controlled or removed.

 This is not the case. Sometimes removal or elimination

of just only one link or chain may be sufficient to
control disease, provided that link is sufficiently
important in the pathogenetic process.
Iceberg Phenomenon
The pattern of disease encountered in a
hospital is quite different from that in a
community.
In the community a far larger proportion of
disease (e.g. diabetes, hypertension) is
hidden from the view of the general public
or physician.
A concept closely related to the spectrum of
disease is the concept of the iceberg
phenomenon of disease. According to this
concept, disease in a community may be
compared with an iceberg. The floating tip of
the iceberg represents what the physician sees in
the community, i.e., clinical cases.
The vast submerged portion of the iceberg
represents the hidden mass of disease, i.e.,
latent, in apparent, pre-symptomatic and
undiagnosed cases and carriers in the
community. The “waterline” represents the
demarcation between apparent and in apparent
disease.
 In some diseases (e.g., hypertension, diabetes, anaemia,
malnutrition, mental illness) the unknown morbidity (i.e., the
submerged portion of the iceberg) far exceeds the known
morbidity.
 The hidden part of the iceberg thus constitutes an important,
undiagnosed reservoir of infection or disease in the community,
and its detection and control is a challenge to modern techniques
in preventive medicine.
 One of the major deterrents in the study of chronic diseases of
unknown aetiology is the absence of methods to detect the
subclinical state – the bottom of the iceberg.
Diagnosed diseases:
 May include controlled and uncontrolled diseases.
 These are diseases which are easily and commonly
identified diseases.
 Diseases which are symptomatic.

Undiagnosed diseases:
 Unidentified cases of disease which are not treated due
to its unknown nature.
Wrongly diagnosed disease:
 An inaccurate assessment of a patient’s condition that
sometimes lead to wrong treatment.

Risk Factors for disease:

 People that fall under this category have a high chance of
acquiring a said disease.

Free of risk factors:

 These are people who have low chances of acquiring a
disease.
 People who are considered completely healthy.
 Example: Hypertension
 Diagnosed diseases: Hypertensive patients who are given
medical attention.
 Undiagnosed or wrongly diagnosed diseases: People who
are not aware that they are hypertensive; patients who are
said to be normotensive but are actually hypertensive.
 Risk factors for disease: People with old age;
overweight/obese people; people with unhealthy lifestyle.
 Free of risk factors: Young people with healthy lifestyle
 Epidemiological approach
Epidemiological approach may be defined as a way by
means of which health related status or events are
identified and studied for control of health problems.
 It is the application of the element of epidemiology to
solve any problem.
These elements include frequency, distribution, and
comparison. Epidemiological approach is based on two
major foundations;
Asking questions
Making comparison
Asking question
Epidemiology has been defined as “a means of
learning or asking questions and getting answers
that lead to further questions.”
Epidemiological studies are done to know the
incidence and prevalence of diseases in the
various subgroup of population by time, place
and person.
Epidemiologist asks variety of questions and makes

observations related to nature and extent

(magnitude) of the problem, geographical

distribution (where ?) time trends (when ?) and

personal characteristics of people who get the

disease (who?).
Through queries and observations, the investigator
tries to find out whether there is increase or
decrease in the incidence and prevalence of disease
over a time span, whether the disease occurs more
in women than in men or in a particular age group.
Further questions are asked pertaining to :
causative factors (why a particular problem or a
disease occurred?); preventive and therapeutic
measures which can be implemented to reduce
or get rid of problem; resources required and
difficulties that may be encountered.
Asking questions
 Related to health events
What is the event?
What is its magnitude?
Where did it happen?
When did it happen?
Who are affected?
Why did it happen?
How it will be overcome?
 Related to health action
What can be done to reduce this problem and its
consequences?
How can it be prevented in the future?
What action should be taken by community,
health services, and other sectors?
Where and for whom these activities be carried
out?
What resources are required?
How are the activities to be organized?
What difficulties may arise and how might
they be overcome?
Answer to the above questions may provide
some clues to disease etiology and help the
epidemiologists to guide planning and
evaluation.
Making comparisons

 The basic approach in epidemiology is to make

comparisons and draw inference (conclusion).

 This may be comparisons of two or more groups, one

group having the disease (or exposed to risk factors)
and other groups not having the disease or
comparison between individual.
By making comparison, the epidemiologist’s
tries to find out the crucial difference in the
host and environment factors between those
affected and not affected. In short
epidemiologist weigh, balance and contrasts
to make conclusion from such comparisons.
 In making comparisons both groups should be
similar so that like can be compared with like. For
fact to be comparable they must be accurate and they
must be gathered in an uniform way.

 For e.g. the study and control groups should be

similar with regard to their age and sex composition,
and similar to other relevant variables.
Explain how nurse can use the epidemiological
approach to solve community health problem?

For example a community had been affected by

typhoid.

Related to health event

What is the problem?

 Typhoid
 What is its magnitude?
 About 50- 100 house are affected, so the magnitude is
large.

 Where did it happen?

 It happened in Ramkot VDC ward no 3

 When did it happen?

 It happened on the month of Ashar.
Who are affected?
 Children between the age of 10-15 years are affected.

Why did it happen?

 It happened because of contaminated water,
 Very low literacy rate
 Lack of knowledge about personal hygiene
 Lack of knowledge about food values and balanceddiet
 Lack of safe drinking water
 Poor environmental sanitation
 Delay diagnosis and treatment
 Related to health action or conclusion.

 What can be done to solve the problem?

 Early detection pattern should be done and could manage
fever in their own home or may also refer to the places if
necessary.
 What action can be done by the community?
 Community people should manage clean and safe drinking
water, as well as clean environment proper disposal of waste
products and they also can use different technical skills like
 How can it be prevented in future?
 It can be prevented by providing safe drinking water, by
making water purified by giving them health education
on water purification and also on proper disposal of
excreta.

 What are the resources for prevention of that disease?

 IEC materials, health personnel’s, organizational help and
money are the main resources for prevention of disease.
How are the activities to be organized?
 The activities are organized through the
coordination with the local leaders, health
organization and community people.
 What difficulties may arise?
In community different kind of difficulties
may arise. The laboratory facility is not
available for the investigation, lack of co-
operation, communication barriers and may be
due to their belief and different altitudes
 Dynamics of disease Transmission (Chain of
Infection)

Source or Reservoir Modes of transmission Susceptible host

Communicable diseases are transmitted from the
reservoir/source of infection to susceptible host.

Basically there are three links in the chain of

transmission, viz, the reservoir, modes of
transmission and the susceptible host.
 Sources or reservoir
• The starting point for the occurrence of a
communicable disease is the existence of a reservoir
or source of infection.
The source of infection is defined as “the person,
animal, object or substance from which an infectious
agent passes or is disseminated to the host (immediate
source).
The reservoir is “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.”
The reservoir and the source of infection are
not always synonymous. E.g. in hookworm
infestation, the reservoir is man but source of
infection is contaminated soil.
In tetanus, the reservoir and source are the
same, that is soil.
Reservoir may be heterogenous or
homogenous.
Infection transmitted from man to man is
homologous.
And if from animal or plants to man is
heterogenous.
TYPES OF RESERVOIRS

Reservoir

Human Animal Non-living

reservoir reservoir reservoir
 Human reservoir

Human reservoir

:Type
•Primary case •Convalescent
Cases •Index case •Healthy
Carriers
•Secondary cases •Incubatory

:According to spectrum of disease

•Clinical cases :Portal of exit
(mild/severe-typical/atypical) •Urinary
•Sub-clinical cases •Intestinal
•Latent infection cases •Respiratory
•others
1. Human reservoir

 By far the most important source or reservoir of

infection for humans is man himself.

 He may be a case or carrier.

A. Cases

A case is defined as “a person in the population or

study group identified as having the particular disease,

health disorder, or condition under investigation”

Types
• Clinical cases (mild/severe-typical/atypical)

• Sub-clinical cases

• Latent infection cases

a. Clinical cases:
The clinical cases may be mild or moderate, severe or
fatal depending up on the level of involvement. This
is clinically diagnosed disease with having sign and
symptoms.
Epidemiologically, mild cases may be more important
sources of infection than severe cases because they
are ambulant and spread the infection wherever they
go, whereas severe cases are usually confined to bed.
b. Sub-clinical cases:

Subclinical cases are variously referred to as

inapparent, covert, missed or abortive cases.

They are equally important as sources of infection.

The disease agent may multiply in the host but does

not manifest itself by signs and symptoms.

The disease agent is, eliminated and

contaminates the environment in the same way

as clinical cases.

The disease is not diagnosed clinically with

sign and symptoms but can be detected by

laboratory test. E.g. Hepatitis A and B

c. Latent infection:
The infectious agent lies in dormant form with in the
host without symptoms and often not presence in
blood, tissue or body secretion of host.
E.g., window period in HIV infection
Primary case
 First case of communicable disease introduced into the
population unit being studied.

Index case
 Person that comes to attention of public health authorities

Secondary case
 Person who acquires the disease from an exposure to the
primary case
Suspect case – An individual (or a group)
who has all of the signs and symptoms of a
disease or condition, yet has not been
diagnosed as having the disease or had the
cause of the symptoms connected to the
suspected pathogen.
 B. Carriers

 It is “an infected person or animal that harbors a

specific infectious agent in the absence of discernible
(visible) clinical disease and serves as a potential
source of infection to others.
 It occurs either due to inadequate treatment or
immune response, the disease agent is not completely
eliminated, leading to a carrier state.
In some disease, either due to inadequate
treatment or immune response, the disease
agent is not eliminated, leading to carrier
state.
Three elements have to occur to form a carrier state:
1. The presence of the disease agent in the body.
2. The absence of recognizable symptoms and signs
of disease.
3. The shedding of disease agent in the discharge or
excretions.
 Classification of carriers
A. According to type
 Healthy carrier: is a person or other organism that has
become infected with a pathogen, but who display no signs or
symptoms. (very dangerous). E. g. diphtheria,

 Incubatory carrier: a person who shed the microorganism

during the incubation period (especially last days of the
incubation period) e.g. mumps, measles and diphtheria.
Convalescent carrier: a person who is clinically
recovered from an infectious disease but still capable
of transmitting the infectious agent to others. E.g.
typhoid, dysentery and whooping cough. (3 weeks to
3 months)
B. According to the port of exit
 Carriers may also be classified according to the portal of
exit of the infectious agent.
 Thus we have urinary carriers, intestinal carriers,
respiratory carriers, nasal carriers, etc.
 Skin eruptions, open wound and blood are also portals
of exit.
 Respiratory carrier: e.g. meningococcus
 Fecal (intestinal) carrier: e.g. typhoid, dysentery, cholera
 Blood carrier: e.g. hepatitis B and AIDS
 Urinary or sexual carrier: e.g. gonococcus, AIDS
 Animal reservoir
The source of infection may sometimes be animals
and birds.
These, like the human sources of infection, may be
cases or carriers.
Zoonosis is an infection that is transmissible under
natural conditions from vertebrate animals to man.
There are over 100 zoonotic diseases which may be
conveyed to man from animals and birds.
E.g. rabies, plague, bovine tuberculosis.
Reservoir in non living things
Soil and inanimate matter can also act as reservoir of
infection.
For example, soil may harbor agents that causes
tetanus, anthrax.
Mode of transmission
Modes of disease transmission

 Communicable disease may be transmitted from

the reservoir or source of infection to a susceptible
individual in many different ways, depending upon
the infectious agent, portal of entry and local
ecological condition.
 Modes of transmission of infectious diseases can
be classified as below ：
1. Direct transmission
 Direct contact
 Droplet infection
 Contact with soil
 Inoculation into skin or mucosa
 Transplacental

2. Indirect transmission
 Vehicle borne
◦ Water

◦ Food/milk
Vector borne
◦ Mechanical
◦ Biological
Air borne
◦ Droplet nuclei
◦ Dust
Fomites borne
Unclean hand and finger
 I. Direct transmission
1. Direct contact
 Direct transmission is the immediate transfer
of the infectious agent from the reservoir to a
new host with no intervening agents.
Infection may be transmitted by direct contact
from skin to skin, mucosa to mucosa or mucosa
to skin of the same or another person e.g.
during touching, kissing, sexual intercourse or
continue direct close contact. E.g. STD, AIDS,
leprosy, scabies, and eye infection.
2. Droplet infection
 This is direct projection of a spray of droplets of saliva
and nasopharyngeal secretion during coughing,
sneezing, speaking, spitting, talking in the surroundings
atmosphere.
 The expelled droplets may stick directly into
conjunctiva, or respiratory mucosa or skin. The droplet
spread is usually limited to a distance of 30-60 cm
between the source and the host.
 Droplet contain millions of bacteria, viruses
which are source of infection (common cold,
diphtheria, pertusis, TB etc.), eruptive fever
(measles).

 The favorable condition is close proximity,

overcrowding and lack of ventilation.
3. Contact with soil
 Disease transmitted by direct exposure of susceptible
tissue to the disease agent in soil e.g. hookworm, T.T.
etc.

4. Inoculation into skin

 Disease agent may be inoculated directly into the skin
or mucosa e.g. rabies virus by dog bites, hepatitis B and
AIDS through contaminated needle etc.
5.Transplacental (vertical) transmission
Disease transmitted through placenta from mother to
fetus is vertical transmission. E.g TORCH
(toxoplasmosis, rubella, cytomegalovirus, herpes
virus) AIDS, hepatitis B, syphilis etc.
II. Indirect transmission
 This is a transmission of infection by indirect means.
Indirect transmission occurs when the infectious agent is
transmitted by an agent either a vehicle or vector.

 For indirect transmission, the infectious agent must be

capable of surviving outside the human host and must
have properties to survive and maintain its pathogenesis
virulence till it finds a new host.
The disease causing micro-organism is
transmitted through various mechanisms as
traditional 5 F’s e.g. flies, fingers, fomites,
food and fluid. Indirect transmission occurs in
various ways:
1. Vehicle borne
 Transmission of infectious agent through the agency of water,
food including (raw vegetables, fruits, milk and milk
products), blood, serum, plasma or other biological products
such as tissue and organs.

 Water and food are the most frequent vehicle of transmission.

Disease transmitted by water and food are mainly the disease
of gastrointestinal tract e.g. acute diarrhea, typhoid
fever ,cholera ,polio, hepatitis A, food poisoning, intestinal
parasite etc.
Disease transmitted by blood include hepatitis
B, AIDS, syphilis etc.
Water borne disease: diarrhea, typhoid,
cholera, polio, dysentery and worm infestation
Food: food poisoning, typhoid, dysentery,
cholera.
2. Vector borne
 In epidemiology vector is defined as an arthropod or any living
carrier like flies, mosquito, rodents, etc that transport an
infectious agent to a susceptible individual (host). Transmission
by vector may be mechanical and biological.

I. Mechanical transmission
 The infectious agent mechanically transported by crawling or
flying anthropod through soiling of its feet or by passage of
organism through its gastro intestinal tract and passively
excreted. There is no development or multiplication of the
infectious agent on or within the vector.
II. Biological transmission
 The infectious agent undergoes replication or development or
both in the vector and requires an incubation period before
vector can transmit. They are of three types:
 Propagative (agent merely multiplies in vector but no change
in form) e.g. plague bacilli in rat.
 Cyclo development (agent only develops but does not multiply
in vector ) e.g. microfilaria in mosquito.
 Cyclo propagative (agent changes in form and number) e.g.
malaria parasites in mosquito.
3. Air borne

I. Droplet nuclei

Droplet nuclei are minute particles concerned in the

spread of air borne infection. This is direct projection

of a spray of droplets of saliva and nasopharyngeal

secretion, talking in the surrounding atmosphere.

 They are tiny particles. They represent the dried
residue of droplets. The diseases transmitted by
droplet spread include respiratory infection
(common cold, diphtheria, pertusis, TB, measles).
The potential for droplet spread is increases in
conditions of close proximity, overcrowding and
lack of ventilation.
II. Dust
 Dust some of the larger droplets which are expelled during
talking, coughing, or sneezing settle down by weight on the
floor, carpet, furniture, clothes, bedding linen and other objects
in the immediate environment and become part of dust.

 A variety of infectious disease caused by this is TB, pneumonia,

streptococcal infection, staphylococcal infection and mostly
common in hospital acquired infection.
4. Fomites borne
 Fomites are inorganic articles or substances other than water and
food contaminated by the infectious agent from a patient and
capable of harboring and transferring the infectious agent to a
healthy person.
 E.g. toys, handkerchief, pencil, pen, dolls, books, drinking
glasses, computer, linen, door’s handle etc. fomites plays an
important role in indirect transmission.
 Disease transmitted by fomites includes diphtheria, typhoid,
bacillary dysentery, hepatitis A, eye and skin infection etc.
5. Unclean hand and fingers
 Hands are the most common medium by which pathogenic
agents are transferred to food from the skin, nose, bowel as
well as from other foods.

 The transmission take place both directly (hand and mouth)

and indirectly e.g. staphylococcal and streptococcal
infection, typhoid fever, hepatitis A and E and intestinal
parasite, unclean hand and fingers mean lack of personal
hygiene.
 (III): Susceptible host

 Host means a human or an animal that provides adequate living

conditions for any given infectious agent. For an infectious
agent to enter, there must be port of entry. There are many ports
of entry as respiratory, alimentary, genitourinary, skin etc.
 After entering into host, the organisms must reach the
appropriate tissue or site of infection in the body of the host,
where it finds optimum condition for its multiplication and the
survival.
Then the agent finds a way to exit from the body in
order to reach a new host. When there is no port of
exit,, the infection continues the body which leads
to many complications including death. After
leaving the human body, the organism must survive
in the external environment for sufficient period till
a new host is found.
 An infectious agent seeks a susceptible host
aiming “successful parasitism”.
 Four stages are required for successful parasitism:
1. Portal of entry
2. Site of election inside the body
3. Portal of exit
4. Survival in external environment
Level of disease prevention and
modes of intervention
Successful prevention depend upon a
knowledge of causation, dynamics of
transmission, identification of risk factors and
risk groups, availability of prophylactic or early
detection and treatment measures, an
organization for applying these measures.
 Epidemiology by identifying modifiable causes of
disease, can play a central role in prevention.

 Disease prevention includes measures not only to

prevent the occurrence of disease, such as risk factor
reduction, but also to detention its progress and
reduce its consequences once established.
It has been defined in term of four
level

Primordial prevention
Primary prevention
Secondary prevention
Tertiary prevention
 Primordial prevention
Primordial prevention, a new concept, is receiving

special attention in the prevention of chronic diseases.

Prevention of the emergency or the development of

risk factors in population or countries in which they

have not yet appeared.

It consist of action and measures that inhibit the

emergence of risk factor.

Efforts are directed towards discouraging
people from adopting harmful lifestyle/habits
through individual and mass education.
 Primordial prevention begins in childhood when
health risk behavior begins. For examples:
 National programme and policies on:
◦ Food and nutrition
◦ Comprehensive policies for discourage smoking,
alcohol and drugs
◦ To promote regular physical activity
◦ Making major changes in lifestyle
 Primary prevention
 An action taken prior to the onset of disease, which
removes the possibility that the disease will ever occur.

 Intervention is done in the pre-pathologic state; to stop

something from ever happening.

 Primary prevention strategies emphasize general health

promotion, risk factor reduction, and other health
protective measures.
 These strategies include health education and health
promotion programs designed to foster healthier
lifestyles and environmental health programs designed
to improve environmental quality.

 It includes the concept of positive health, that

encourages the achievement and maintenance of an
“acceptable level of health that will enable every
individual to lead a socially and economically
productive life
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
Population (mass) strategy:
Directed at the whole population irrespective of
individual risk levels.

The population approach is directed towards

socioeconomic, behavioral and lifestyle changes.
High-risk strategy:
The high-risk strategy aims to bring preventive care
to individuals at special risk.

This requires detection of individuals at high risk

by the optimum use of clinical methods.
 Examples:
 Health promotion
 Health education. health education to improve healthy
habits and health consciousness in the community.
 Environmental modification: healthful physical
environment(housing, water supply, excreta disposal),
good working condition
 Risk assessments for specific disease
 Life style change and Behavior changes
Nutritional intervention: improvement of the
nutritional standards of the community. Food
distribution and nutritional improvements of
vulnerable groups.
Family planning services and marriage
counseling
Genetic screening
 Specific protection.
 Immunization

 Use of specific nutrients(vitamin A for children, iron

and folic acid for pregnant)
 Chemoprophylaxis(tetracycline for cholera, dapsone
for leprosy, chloroquine for malaria)
 Protection against occupational hazards
 Protection against accident(use of helmets, seatbelts)
 Control of environment
SECONDARY PREVENTION
 Secondary prevention focuses on individuals who experience
health problems or illness and who are at risk of developing
complication or worsening conditions.
 Action which halts the progress of a disease at its incipient
stage and prevents complications.
 Activities are directed at early detection of disease and
prompt intervention and health management, thereby
reducing severity and enabling the client to return to normal.
 Secondary prevention aims to reduce the more
serious consequences of disease through early
diagnosis and treatment. And to reduce the
prevalence of diseases.

 Its purpose is to cure disease, slow its progression,

or prevention of complications and disabilities on
individuals or communities
 Examples:
Screening surveys and procedures of any type
Encouraging regular medical and dental
checkups
Teaching self examination for breast and
testicular cancer
Assessing the growth an development of
children
 Nursing assessment and care provided in home,
hospital or other agency to prevent complications (e.g.,
maintaining skin integrity; turning; positioning; and
exercising clients; ensuring adequate rest; food and
fluid intake; promoting fecal and urinary elimination;
administering medical therapies such as medications)
 Case finding measure
 Adequate treatment to arrest disease process and
prevent further complication.
 TERTIARY PREVENTION
 Tertiary prevention aimed at reducing the progress or
complications of established disease and is an important
aspect of therapeutic and rehabilitation medicine.

 It consists of the measures intended to reduce impairments

and disabilities, minimize suffering caused by poor health
and promote patients’ adjustment to incurable conditions.
Its focus is to help rehabilitate individuals and
restore them to an optimum level of
functioning within the constraints of the
disability.
It involves minimizing the effects of long-term
disease or disability by interventions direct at
preventing complications and deteriorations.
Tertiary Prevention strategies are both
therapeutic and rehabilitative measures once
disease is firmly established.
Examples:
Teaching a client who has disabilities to identify
and prevent complications.
Referring a client with a spinal cord injury to a
rehabilitation center to receive training that will
maximize use of remaining abilities.
Teaching a client to use crutches
Undergone speech therapy

Attend self management education for

diabetes

Physical therapy after CVA.

Reconstruction surgery in leprosy

Establishing school for blind.

 Modes of intervention
Intervention can be defined as any attempt to
intervene(interfere) or interrupt the usual sequence in the
development of disease in man.

Five modes of intervention:

1. Health promotion

2. Specific protection

3. Early diagnosis and treatment

4. Disability limitation

5. Rehabilitation
Health promotion:
Health promotion is the process of enhancing health
and reducing risk of ill health through the
overlapping spheres health education, health
protection and disease prevention.
It is not directed against any particular disease, but
is intended to strengthen the host through a variety
of approaches.
The well known interventions are:
A. Health education
B. Environmental modifications
C. Nutritional interventions
D. Lifestyle and behavioral changes
A. Health education
One of the most cost effective interventions.
A large number of diseases could be prevented with
little or no medical intervention if people were
adequately informed about them and if they were
encouraged to take necessary precautions in time.
B. Environmental modifications
A comprehensive approach to health
promotion requires environmental
modifications, such as provision of safe water;
installation of sanitary latrines; control of
insects and rodents; improvement of housing,
etc.
The history of medicine has shown that
many infectious diseases have been
successfully controlled in western countries
through environmental modifications, even
prior to the development of specific vaccines
or chemotherapeutic drugs.
C. Nutritional Interventions
These comprise food distribution and
nutrition improvement of vulnerable groups;
child feeding programmes; food fortification;
nutrition education, etc.
D. Lifestyle and behavioral changes
The action of prevention in this case, is one
of individual and community responsibility
for health, the physician and in fact each
health worker acting as an educator than a
therapist.
Health education is a basic element of all
health activity.
It is of paramount importance in changing
the views, behavior and habits of people.
Specific protection:
 The following are some of the currently available
interventions aimed at specific protection: immunization;
use of specific nutrients; chemoprophylaxis; protection
against occupational hazards; protection against accidents;
protection from carcinogens; avoidance of allergens; control
of specific hazards in the general environment; control of
consumer product quality and safety of foods, drugs,
cosmetics, etc.
Early diagnosis and treatment:
In order to prevent overt disease or disablement, the
criteria of diagnosis should, if possible, be based on
early biochemical, and functional changes that
precede the occurrence of manifest signs and
symptoms.
The earlier a disease is diagnosed and treated the
better it is from the point of view of prognosis and
preventing the occurrence of further cases or any
long-term disability.

.
Disability limitation:
 The objective of this intervention is to prevent or halt the
transition of the disease process from impairment to
handicap.

 While impairment which is the earliest stage has a large

medical component, disability and handicap which are later
stages have large social and environmental components in
terms of dependence and social cost.
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.

 It includes all measures aimed at reducing the impact or

disabling and handicapping conditions and at enabling the
disabled and handicapped to achieve social integration.
Medical rehabilitation – restoration of function.
Vocational rehabilitation – restoration of the
capacity to earn a livelihood.
Social rehabilitation – restoration of family and
social relationships.
Psychological rehabilitation – restoration of
personal dignity and confidence.
Examples of rehabilitation: establishing schools for
the blind, provision of aids for the crippled,
reconstructive surgery in leprosy, muscle exercises
in neurological disorder.
 Disease prevention and control
Infectious disease control and prevention is the breaking
the chain of infection.
Disease control involves all the measures designed to
prevent or reduce as much as possible the incidence,
prevalence and consequences of disease.
This includes community participation, political support
and inter-sectoral coordination. Control measures should
not be delayed.
 The following are the main method of infectious
disease control and prevention.

A. Controlling the reservoirs (early diagnosis,

notification, isolation, treatment and
quarantine).
B. Interruption of transmission
C. Protecting the susceptible host
 A. CONTROLLING THE RESERVOIR

The most desirable control measure would be

to eliminate the reservoir or source, if that
could be possible.
The general measures of reservoir control
comprises:-
Early diagnosis, notification, isolation,
treatment, quarantine, surveillance and
disinfection - all directed to reduce the
quantity of the agent available for
dissemination.
 1. Early diagnosis

1st step in the control of communicable disease is the

rapid identification.

This is a very much important activity for disease

control. Frequently laboratory procedures may be
required to confirm the diagnosis.
Early diagnosis is needed for:
(a) the treatment of patients
(b) for epidemiological investigations, e.g., to
trace the source of infection
(c) to study the time, place and person distribution
(d) for the institution of prevention and control
measures.
 2. Notification

Once an infectious disease has been detected or

even suspected, it should be notified to the local
health authority whose responsibility is to control
measures including the provision of medical care to
patients.

Notification is an important source of

epidemiological information.
 It enables early detection of disease outbreaks,
which permits immediate action to be taken by
the health authority to control there spread.

 Example: measles outbreak can be controlled if

only single case can be notified properly in time.
Notification of infectious diseases is often made
by the attending physician or the head of the
family, but any one, including the lay people
(e.g., religious, political and administrative
leaders, teachers and others) can report, even on
suspicion. In all cases, the diagnosis is verified
by the local health authority.
 3. Isolation
 Isolation is oldest communicable disease control measure.
 It is defined as "separation for the period of
communicability of infected persons or animals from
others in such places and under such conditions, as to
prevent or limit the direct or indirect transmission of the
infectious agent from those infected to those who are
susceptible, or who may spread the agent to others“
The purpose of isolation is to protect the
community by preventing transfer of
infection from the reservoir to the possible
susceptible hosts.
 4.Treatment
Many communicable disease have been controlled
by effective drugs. The objective of treatment is to
kill the infections agent when it is still in the
reservoir.
Treatment reduces the communicability of disease,
short the duration of illness and prevent
development of secondary cases.
In some disease e.g. syphilis, TB, and
leprosy early diagnosis and treatment is of
primarily importance in interrupting
transmission. Treatment is also extended to
carriers.
 Cont…
Treatment can take the form of individual treatment or
mass treatment.
In the latter category, all the people in the community
are administrated the drugs whether they have the
disease or not (e.g. trachoma)
 5. Quarantine
 Quarantine has been defined as the limitation of freedom of
movement of such well persons or domestic animals exposed
to communicable disease for a period of time not longer than
usual incubation period of the disease in such manner as to
prevent effective contact with those not so exposed.
 The purpose of quarantine is to prevent effective contact
with those people not so exposed.
 Quarantine measures are also "applied by a health
authority to a ship, an aircraft, a train, road vehicle, other
means of transport or container, to prevent the spread of
disease, reservoirs of disease or vectors of disease".
 Quarantine may comprise absolute quarantine, modified
quarantine, e.g., a selective partial limitation of freedom
of movement, such as exclusion of children from school
which has been defined as the separation for special
consideration.
 B. INTERRUPTION OF
TRANSMISSION
A major aspect of communicable disease control
relates to "breaking the chain of transmission" or
interruption of transmission.
This mean changing some components of man's
environment to prevent the infective agent from a
patient or carrier from entering the body of
susceptible person.
 For example, water can be a medium for the transmission of

many diseases such as typhoid, dysentery, hepatitis A, cholera.

Water treatment will eliminate these diseases.

 Food born disease is particularly prevalent in areas having low

standards of sanitation. Clean practices such as hand washing,

adequate cooking, prompt refrigeration of prepared foods and

withdrawal of contaminated foods will prevent most food-

borne illnesses .
When the disease is vector-borne, control measures
should be directed primarily at the vector and its
breeding places. Vector control also includes
destruction of stray dogs, control of cattle, pets and
other animals to minimize spread of infection
among them, and from them to man.
Maintain clean environment
Reduce pollution
 C. PROTECTING THE SUSCEPTIBLE
HOST
 The third link in the chain of transmission is the susceptible
host or people at risk. The susceptible host can be protected by
following methods:

i. Active immunization

ii. Passive immunization

iii. Combined passive and active immunization

iv. Chemoprophylaxis

v. Non-specific measures
i. Active immunization:
One of effective way of controlling the spread of
infection is to strengthen the host defenses. It is one of
the most powerful and cost-effective weapons of
modern medicine.
There are some infectious diseases whose control is
solely based on active immunization. Active
immunization produce antibodies for specific disease
prevention e.g.:- BCG, DPT, Polio, Measles, Hepatitis
etc.
 Vaccination against these diseases is given as a routine

immunization during infancy and early childhood with

periodic boosters to maintain adequate levels of

immunity.

 There are immunizations against certain diseases

which are offered to high risk groups or restricted to

definite geographic areas where the disease is endemic

or a public health problem (e.g JE)

Immunization is a mass means of protecting
the greatest number of people. By reducing the
number of susceptibles in the community, it
augments "herd immunity" making the
infection more difficult to spread.
 Immunization has to be planned according to
the needs of the situation.
 ii. Passive immunization:

It is the transfer of antibodies to induce protection

against disease. Passive immunization is a short-term
useful only when exposure to infection has just
occurred. E. g.:- Rabies vaccination, tetanus toxoid,
Anti-snake venom etc.
 iii. Combined passive and active
immunization:
In some particular disease, the combined method is
effective e. g, hepatitis B.
Hepatitis B vaccination + Hepatitis B
immunoglobulin ( in case of Hep. B exposure)
 iv. Chemoprophylaxis:

Administration of drugs before or after

exposure in certain factors or disease agent but
sign and symptoms of disease has not been
developed.
E.g. Plague : Tetracycline for contacts of
plague
Bacterial conjunctivitis: Erythromycin
 v. Non-specific measures:

Most of the non-specific measures to interrupt

pathways of transmission are in general applicability.

Improvement in the quality of life (better housing,

water supply, sanitation, nutrition education) fall in
to this category.
 Non- specific measures will also include
‘legislative measures’ such as pollution in control.

 Another important non-specific measure is

community involvement in disease surveillance,
disease control and other public health activities.
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