2nd Year B.Sc Nursing Community Health Nursing – IEPIDEMIOLOGY By, M. Thiru Murugan UNIT-III: EPIDEMIOLOGY: Definition, concept, aims, scope, uses and terminology used in epidemiology Dynamics of disease transmission : epidemiological triad Morbidity and mortality : measurements Levels of prevention Methods of epidemiology: Descriptive Analytical: Epidemic investigation Experimental Epidemiology INTRODUCTION: Epidemiology is derived from Greek word “epidemic” EPI – up on, DEMOS – people; LOGOS – study. Epidemiology means the study of disease in human population. DEFINITION: “epidemiology is defined as the study of the distribution and determinants of health related states or events in specified populations and the application of this study to control the health problems”.  Concepts Basic to Epidemiology: Host, Agent, and Environment Model: Host: The host is a susceptible human or animal who harbors and nourishes a disease causing agent. Many physical, psychological, and lifestyle factors influence the host's susceptibility and response to an agent. Concepts Basic to Epidemiology: Agent: An agent is a factor that causes to a health problem or condition. Causative agents can be Biological, Physical, Psychological, Economical, Nutritional, Environmental etc.. Concepts Basic to Epidemiology: Environment: The environment refers to all the external factors surrounding the host that might influence vulnerability or resistance. The physical environment The psychosocial environment AIMS OF EPIDEMIOLOGY Aims: to describe the distribution and size of disease problems in human population. to identify the etiological factors. to provide the data essential to the planning, implementation and evaluation. SCOPE OF EPIDEMIOLOGY I. According To Disease Group: Infectious Disease Epidemiology Cardio Vascular Epidemiology Cancer Epidemiology II. According To Group Of Factors Nutritive Epidemiology Reproductive Epidemiology Environmental Epidemiology Clinical Epidemiology Molecular Epidemiology Genetic Epidemiology Computational Epidemiology USES OF EPIDEMIOLOGY Identify the causes of diseases. Helps to describe the health status of the population. Control the disease transmission. Planning, implementing and evaluating health programmes on evidence basis. TERMINOLOGIES USED IN EPIDEMIOLOGY INFECTION: The entry and development or multiplication of an infectious agent in the body of man or animal. ENDEMIC: The constant presence of a disease or infectious agent within a given geographical area or population group, without importation from outside. EPIDEMIC: an out break of disease in a community in excess of normal expectation and derived from a common or propagated source. SPORADIC: The cases occurs irregularly, haphazardly from time to time and generally infrequently. TERMINOLOGIES USED IN EPIDEMIOLOGY PANDEMIC: An epidemic which spreads from country to country or over the whole world. ZOONOSES: Diseases or infections which are natu

1. 2nd Year B.Sc Nursing
Community Health Nursing –
I
EPIDEMIOLOGY
By,
M. Thiru Murugan

2. UNIT-III: EPIDEMIOLOGY:
• Definition, concept, aims, scope, uses and
terminology used in epidemiology
• Dynamics of disease transmission : epidemiological
triad
• Morbidity and mortality : measurements
• Levels of prevention
• Methods of epidemiology:
• Descriptive
• Analytical: Epidemic investigation
• Experimental

3. Epidemiology
• INTRODUCTION: Epidemiology is derived from
Greek word “epidemic”
• EPI – up on, DEMOS – people; LOGOS – study.
Epidemiology means the study of disease in human
population.
• DEFINITION: “epidemiology is defined as the
study of the distribution and determinants of health
related states or events in specified populations and
the application of this study to control the health
problems”.

4. Concepts Basic to Epidemiology:
• Host, Agent, and Environment Model:
• Host: The host is a susceptible human or
animal who harbors and nourishes a
disease causing agent. Many physical,
psychological, and lifestyle factors
influence the host's susceptibility and
response to an agent.

5. Concepts Basic to Epidemiology:
• Agent: An agent is a factor that
causes to a health problem or
condition.
• Causative agents can be Biological,
Physical, Psychological, Economical,
Nutritional, Environmental etc..

6. Concepts Basic to Epidemiology:
• Environment: The environment refers to
all the external factors surrounding the
host that might influence vulnerability or
resistance.
• The physical environment
• The psychosocial environment

7. AIMS OF EPIDEMIOLOGY
• Aims:
• to describe the distribution and size of
disease problems in human
population.
• to identify the etiological factors.
• to provide the data essential to the
planning, implementation and
evaluation.

8. SCOPE OF EPIDEMIOLOGY
I. According To Disease Group:
• Infectious Disease Epidemiology
• Cardio Vascular Epidemiology
• Cancer Epidemiology
II. According To Group Of Factors
• Nutritive Epidemiology
• Reproductive Epidemiology
• Environmental Epidemiology
• Clinical Epidemiology
• Molecular Epidemiology
• Genetic Epidemiology
• Computational Epidemiology

9. USES OF EPIDEMIOLOGY
1. Identify the causes of diseases.
2. Helps to describe the health status of
the population.
3. Control the disease transmission.
4. Planning, implementing and
evaluating health programmes on
evidence basis.

10. TERMINOLOGIES USED IN
EPIDEMIOLOGY
• INFECTION: The entry and development or
multiplication of an infectious agent in the body of man
or animal.
• ENDEMIC: The constant presence of a disease or
infectious agent within a given geographical area or
population group, without importation from outside.
• EPIDEMIC: an out break of disease in a community in
excess of normal expectation and derived from a
common or propagated source.
• SPORADIC: The cases occurs irregularly, haphazardly
from time to time and generally infrequently.

11. TERMINOLOGIES USED IN EPIDEMIOLOGY
• PANDEMIC: An epidemic which spreads from country to
country or over the whole world.
• ZOONOSES: Diseases or infections which are naturally
transmitted between vertebrate animals and men.
• INCUBATION PERIOD: This is the time interval between
the entry of the disease agent into the body and the
appearance of first sign and symptom of the disease.
• CARRIER: A person who harbors the disease agent
without having any outward signs and symptoms.
• ISOLATION: A separation of a person with infectious
disease from contact with other human beings for the period
of communicability.

12. TERMINOLOGIES USED IN EPIDEMIOLOGY
• PATHOGENICITY: Ability to cause the disease.
• CONTAGIOUS: A disease that is transmitted through
contact.
• RESERVOIR: The habitat ( place for living) where an
infectious agent living, grows and multiplies.
• VIRULENCE: Measure the severity of disease.
• FOMITES: Inanimate articles other than food or water
contaminated by the infectious discharges.
• VECTOR: Usually an arthropod eg. Mosquito which
transfers an infectious agent from an infected person to
a healthy person.

13. Dynamics of disease transmission:
There are 3 link of disease transmission:
Source or
Reservoir
Mode of
transmission
Susceptible
Host

14. • I. SOURCE & RESERVOIR:
• SOURCE: The source defined as the “person, animal,
object or substance from which an infectious agent passes
or disseminated to the host”.
• RESERVOIR: A reservoir is defined as “any person,
animal, arthropod, plant, soil or substance in which an
infectious agent lives and multiplies , on which it depends
primarily for survival, and where it reproduces itself in
such manner that it can be transmitted to a susceptible
host”.
• Types of reservoir:
1. Human reservoir
2. Animal reservoir
3. Reservoir in non living things

15. • 1. HUMAN RESERVOIR:
• The most important source or reservoir of infection
for human is man himself.
• Human may be A) Case B) Carrier
• A) CASES: A case is defined as “ a person in the
population having the particular disease, health
disorder or condition under investigation”. The
presence of infection in host may be :-
i. Clinical
ii. Sub clinical
iii. Latent

16. i. Clinical illness: Clinical illness may be
mild or moderate, typical or atypical, severe
or fatal.
ii. Sub clinical cases: Sub clinical cases are
also known as in apparent, missed or
abortive cases. The disease agent may
multiply in the host but does not manifest
itself by signs and symptoms. Sub clinical
infection may be detected only by
laboratory tests.
iii. Latent infection: Infectious agent lies
dormant within the host without symptoms.

17. • B) CARRIERS: A carrier is defined as an infected
person or animal that harbors' a specific infectious agent
and serves as a potential source of infection for others.
• Classification of carriers:
TYPE:
i. Incubatory
ii. Convalescent
iii. Healthy
DURATION: i)Temporary ii)Chronic
PORTAL OF EXIT:
i. Urinary
ii. Intestinal
iii. Respiratory
iv. Others

18. A. TYPE:
i. Incubatory carriers: Carriers which
spread the infectious agent during the
incubation period of disease.
ii. Convalescent carriers: Carriers which
continue to spread disease during the period
of convalescence.
iii. Healthy carriers: They are victims of sub
clinical infection who have developed
carrier state without suffering from overt
disease.

19. • B. DURATION:
i. Temporary carriers: Carriers which spread infectious
agent for short period of time
ii. Chronic carriers: Carriers which spread infectious
agent for indefinite period
• C. PORTAL OF EXIT: Urinary, Intestinal, Respiratory,
Others –(skin eruptions, open wounds, blood)
• 2. ANIMAL RESERVOIR: The source of infection may
sometimes be animals and birds. The diseases and
infections which are transmissible to man from vertebrate
are called Zoonoses. E.g. :- Rabies, Yellow Fever,
Influenza
• 3. RESERVOIR IN NON LIVING THINGS: Soil and
inanimate matter can also act as reservoir of infection

20. • A. DIRECT
TRANSMISSION:
1. Direct contact
2. Droplet infection
3. Contact with soil
4. Inoculation into skin
5. Trans placental
• B. INDIRECT
TRANSMISSION:
1. Vehicle borne
2. Vector borne
3. Air borne
4. Fomite borne
5. Unclean hands/fingers
II. MODE OF TRANSMISSION

21. A. DIRECT TRANSMISSION
1. Direct contact: Infection may be transmitted
by direct contact from skin to skin, mucosa to
mucosa, or mucosa to skin.
2. Droplet infection: This is direct projection of
spray of droplets of saliva and nasopharyngeal
secretions during coughing, sneezing, talking
or spitting. The droplet spread is usually
limited to a distance of 30-60 cm between
source and host.

22. A. DIRECT TRANSMISSION
3. Contact with soil: The disease agent may be
acquired by direct exposure to the disease
agent in the soil. E.g. hook worm, tetanus,
mycosis
4. Inoculation into skin: Disease agent may be
inoculated directly into the skin or mucosa.
E.g. rabies virus by dog bite, Hepatitis B by
contaminated needles
5. Tranplacental transmission: Disease agents
can be transmitted transplacentally. E.g. AIDS

23. B. INDIRECT TRANSMISSION
1. VEHICLE BORNE: Vehicle borne transmission implies
transmission of the infectious agent through the agency of
water, food, raw vegetables, fruits, milk, blood etc.
2. VECTOR BORNE: Classification of vector borne
disease:-
 Invertebrate- E.g. arthropods( flies, mosquitoes, cockroach,
ticks, mites, bugs)
 Vertebrate- E.g. mice, rodents.
3. AIR BORNE : Droplet nuclei & Dust
4. FOMITE BORNE: Fomites are inanimate articles or
substances other than water or food contaminated by
infectious agents. E.g. soiled clothes, syringes, instruments
etc.
5. UNCLEAN HANDS: Lack of personal hygiene favour
person- person transmission of infection.

24. 3. SUSCEPTIBLE HOST
• SUCCESSFUL PARASITISM: 4 stages are there in
successful parasitism
1. PORTAL OF ENTRY: Infectious agent enter the host.
E.g. Respiratory tract, Alimentary tract, Genito urinary
tract, Skin.
2. SITE OF ELECTION: In the body the disease agent
finds appropriate tissue for multiplication and survival.
3. PORTAL OF EXIT: The disease agent finds a way out
of the body.
4. SURVIVAL OUTSIDE: After leaving the human body
the organism must survive in the external environment
for sufficient period till a new host is found

25. Epidemiological Triad

26. Agent
• Biological: (micro-organisms)
• Physical: (temperature, radiation, trauma, others)
• Chemical: (acids, alkalis, poisons, tobacco,
medications / drugs, others)
• Environmental: (nutrients in diet, allergens, others)
• Nutritional: (under- or over-nutrition)
• Psychological: experiences

27. Host
• Genetic
• Immunologic state
• Personal behavior: (life-style
factors): diet, tobacco use, exercise,
etc
• Personal characteristics: Age,
gender, socio-economic status, etc.

28. Environment
Environmental factors are extrinsic factors which
affect the agent and the opportunity for exposure.
These include:
–Physical factors: e.g. geology, climate
(temperature, humidity, rain, etc)
–Biological factors: e.g. insects that transmit an
agent
–Socioeconomic factors: e.g. crowding, sanitation,
and the availability of health services
Phenomena which bring the host and agent
together: vector, vehicle, reservoir, etc

29. Mortality and Morbidity
• Mortality rate or death rate: is a measure of
the number of deaths (in general, or due to a
specific cause) in a particular population. Ex:
Maternal mortality rate, Infant mortality rate,
Child mortality rate.
• Morbidity: Morbidity comes from the
word morbid, which means "or of relating to
disease," like the number of cases of any
disease in an areas.

31. Mortality indicators
• Crude Death rate = No. of death occurred in
an year/ Estimated mid - year population х
1000
• Life expectancy: At birth is “the average
number of years that will be lived by those
born alive into a population if the current age
specific mortality rates persist”
• IMR= No: of death under 1yr / No. of live
birth during that yearх1000

32. Mortality indicators
• NEONATALMORTALITY RATE =
No of death under 28 days of age occurred during a
yr х 1000 . no of live birth during that year.
• MATERNALMORTALITY RATE:
MMR = No of female death from pregnancy, child
birth, or Puerperal causes in an year х1000 no of live
birth in same area during that year.

33. Mortality indicators
• Disease specific mortality: No of Death
occurs due to specific diseases.
• PROPOTIONAL MORTALITY RATE =
No of deaths from the specific disease in year
/Total death from all causes in that year x 100
• CASE FATALITY RATE = total no of death
due to a particular disease / total no of cases
with same disease x100

34. Morbidity indicators -Incidence
• Incidence Rate = No of new case of specific
disease during given time period/ Population at risk
during that period х1000.
• Prevalence = The term disease prevalence refers
specifically to all current cases( old and new)
existing at a given point of time , or over a period of
time in a given population.
• i) Point prevalence ii) Period prevalence

35. LEVELS OF PREVENTION
• Definition of prevention: The management of
those factors that could lead to disease so as to
prevent the occurrence of the disease.
• Level of prevention:
Primordial prevention
Primary prevention
Secondary prevention
Tertiary prevention

36. PRIMORDIAL PREVENTION
• Definition: It is the prevention of
emergence of risk factors in populations,
in which they have not yet appeared .
• INTERVENTIONS: The main
intervention in primordial prevention is
through individual and mass health
education.

37. PRIMARY PREVENTION
DEFINITION: Primary prevention can be
defined as action taken prior to the onset of
disease, which removes the possibility that a
disease will ever occur. It includes
i)Population (mass) Strategy: It is directed at
the whole population.
ii)High- risk Strategy: It aims to bring
preventive care to individuals at special risk.

38. PRIMARY PREVENTION
(INTERVENTIONS)
i)General Health promotion:
1.Health education
2.Environmental
modifications
3.Nutritional interventions
4.Lifestyle and behavioral
changes.
5.Healthful environment
6.Good working condition
7.Marriage Counseling
8.Periodic Selective
examination of risk
population.
ii)Specific protection:
1.Use of Specific
immunization
2.Chemoprophylaxis
3.Use of specific nutrients
4.Protection against accidents
5.Protection against
occupational hazards.
6.Avoidance of allergens.
7.Protection from air
pollution.

39. SECONDARY PREVENTION
Definition: The action which halts the progress of a
disease at its incipient stage and prevents
complications.
Objectives: Complete cure and prevent the
progression of disease process. To prevent the
spreads of disease by curing all the known cases. To
prevent the complications. To shorten the period of
disability.
Interventions: Individual and mass case-finding
measures. Screening surveys, Selective examination

40. • Tertiary prevention:
• Definition: Reduce or limit impairments and disabilities,
minimize suffering
• MODES OF INTERVENTION:
• i)Disability limitation:
• Prevent Disease Impairment, Disability & Handicap
• ii)Rehabilitation:
1. Medical rehabilitation: (restoration Bodily Function).
2. Vocational rehabilitation:( restoration of the capacity to
earn a livelihood)
3. Social rehabilitation: (restoration of family and social
relationship).
4. Psychological rehabilitation: (Restoration of personal
dignity and confidence)

41. Methods of epidemiology

42. Observational Studies
• DEF: Allow nature to take its cause; the
investigator measures but does not
intervene.
• Descriptive epidemiology: It is
concerned with observing the distribution
of disease in human population and
identifying the characteristics with which
the disease seems to be associated.

43. STEPS IN DESCRIPTIVE STUDIES
1) Defining the population to be studied
2) Defining the disease under study
3) Describing the disease by
a) Time
b) Place
c) Person
4) Measurement of disease
5) Comparing with known indices
6) Formulation of an etiological hypothesis

44. Uses of descriptive epidemiology
• It provides data regarding the magnitude of the
disease load and types of disease problems in
terms of morbidity and mortality rates and ratios.
• It provides clue to disease etiology and help in the
formulation of an etiological hypothesis.
• It provides background data for planning,
organizing and evaluating preventive service.
• Contribute to research by describing variations in
disease occurrence by time, place and person.

45. • Analytical epidemiology:
• Def: Second major type of epidemiology. Focus on
individual within population. Analysis relationship
between health status and other factors.
• TYPES:
A. Case control study
B. Cohort study
• A. CASE CONTROL STUDY
• Also known as Retrospective or trohoc study.
• Case ( with disease) and Control (no disease)
selected for study.

47. B. COHORT STUDY
• Also Known as Prospective, longitudinal.
• Incidence and forward-looking study
Distinguishing features:
• Group of peoples are selected on the basis of
exposed to factors or not exposed
• Follow up will be done to find development of
disease.
• The cohorts are identified prior to the
appearance of the disease

49. Experimental or interventional studies
• Involve an active attempt to change a disease
determinant(e.g an exposure or a behaviour)
or the progress of a disaese (through
treatment)
• The studies are based on a group which has
had the experience compared with control
group which has not had the experience.

50. Experimental or interventional
studies
1.Randomized Controlled Trial
2.Quasi-Experimental Designs
3.Field and community trial

51. Randomized Controlled Trial ("RCT"),
(or) "Randomized Clinical Trial"
• The mainstay of experimental medical studies,
normally used in testing new drugs and
treatments.
• Randomly allocated to receive the
experimental treatment.
• The experimental and control groups are then
followed for a set time, and relevant
measurements are taken to indicate the results
(or 'outcomes') in each group.

52. Field and community trial
•General population selected
from community for study.