1. 1st GNM Community H Nsg - Unit 4 Epidemiology.pptx

Community Health Nursing I
Epidemiology
By,
Thiru murugan

UNIT-IV: Principles of Epidemiology and Epidemiological
methods:
a) Definition and aims of epidemiology, communicable and
non-communicable diseases.
b) Basic tools of measurement in epidemiology
c) Uses of epidemiology
d) Disease cycle
e) Spectrum of disease
f) Levels of prevention of disease.
g) Disease transmission – direct and indirect.
h) Immunizing agents, immunization and national
immunization schedule.
i) Control of infectious diseases.
j) Disinfection

• 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
diseases or health problems”.

Terminologies used in epidemiology:
• Infection: the entry and multiplication of an
infectious agent in the body of man or animal.
• Endemic: the constant presence of a disease in
particular area or population. Ex- malaria, dengue,
chikungunya.
• Epidemic: an out break of disease from one area
to other area in a community. Ex - cholera, polio,
small pox
• Sporadic: refers to a disease that occurs
infrequently and irregularly. Ex - Tetanus, rabies,
and plague.

• Pandemic: a disease which spreads from country to
country or over the whole world. Ex - swine flu, HIV,
COVID – 19.
• Zoonosis: diseases or infections transmitted from animals
to men. Ex - rabies.
• Incubation period: this is the time interval between the
entry of the disease agent into the body and the
appearance of first sign & symptom of the disease.
• Carrier: a person who harbors or carry the disease
agent with or without having any outward signs and
symptoms.
• Isolation: a separation of a person with infectious
disease (communicable disease) from contact with other
human beings to avoid spread of disease.

• Quarantine: a quarantine is a restriction on the
movement of people, animals and goods which is
intended to prevent the spread of disease
• 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.

Aims
• To describe the distribution and size of disease problems in
human
• To identify the etiological factors.
• To provide the data (information) essential to the
preparation) implementation (providing) & evaluation
(checking the outcome).
Communicable and non-communicable diseases:
 Communicable diseases are diseases that spread from
person to person. Ex - polio, typhoid, chickenpox, TB,AIDS
 Non-communicable disease (NCD) are disease that is not
spread from one person to another. Ex - most heart diseases,
most cancers, diabetes, chronic kidney disease, hyper
tension.

Basic tools of measurement in epidemiology:
• Mortality rate or death rate: is a measure of the number
of deaths in a particular population. Ex: Maternal mortality
• Morbidity: number of disease in an areas.

Mortality indicators
• Crude Death rate:
Number of death occurred in an year
Estimated mid - year population X 1000
• IMR (Infant Mortality rate):
Number of death under 1yr
Number of live birth during that year X 1000
• Neonatal mortality rate (NMR):
Number of death under 28 days of age occurred during a year
1000 Number of live birth during that year
• Maternal mortality rate (MMR):
Number of female death from pregnancy, child birth, or
puerperal causes in an year X 1000 Number of live birth in same
area during that year.

• Proportional mortality rate:
Number of deaths from the specific disease in year
total death from all causes in that year X 100
• Case fatality rate:
Total Number of death due to a particular disease
total Number of cases with same disease X 100
• Disease specific mortality:
• Number of Death occurs due to specific diseases.
• Life expectancy:
• The average number of years a person can live in a
favorable conditions”

Morbidity indicators
• Incidence Rate:
Number of new case of specific disease during given time period
Population at risk during that period X1000.
• Prevalence: proportion of a particular population found to
be affected by a medical condition (typically a disease or a
risk factor such as smoking or seatbelt use) at a specific
time.
• i) Point prevalence is the proportion of a population that
has the characteristic at a specific point in time.
• ii) Period prevalence is the proportion of a population that
has the characteristic at any point during a given time
period. “Past 12 months” is a commonly used period.

• 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.
• Disease cycle: This cycle includes phases of
growth, change of structure, multiplication /
reproduction, spread of pathogen & infection of a
new host.

The
pathogen
The host
The exit
Transmission
The
environment
The
entry
The
susceptible
person or
animal

• The transmission cycle has different elements:
 The pathogen: the organism causing the infection
 The host: the infected person or animal ‘carrying’ the
pathogen
 The exit: the method the pathogen uses to leave the body
of the host
 Transmission: how the pathogen is transferred from host
to susceptible person or animal
 The environment: the environment in which transmission
of the pathogen takes place
 The entry: the method the pathogen uses to enter the
body of the susceptible person or animal
 The susceptible person: the potential future host who is
receptive to the pathogen

Spectrum of Disease
• The spectrum of disease refers to the range of
manifestations & severities of illness
associated with a diseases, illnesses, or injury.
• The progress of a disease process in an
individual over time, in the absence of
intervention.
• The process begins with exposure to factors
capable of causing disease.
• Without medical intervention, the process
ends with disability, or death

• Infectivity refers to the exposed persons who
become infected.
• Pathogenicity: ability to cause the disease.
• Virulence persons with clinical disease who
become severely ill or die.
• Because of the clinical spectrum, cases of
illness diagnosed by clinicians in the community
often represent only the “tip of the iceberg.”
• Many additional cases may be too early to
diagnose or may remain asymptomatic.

Levels of prevention of disease:
• Definition of prevention: The avoidance of those factors
that could lead to disease.
• Level of prevention:
1. Primordial prevention
2. Primary prevention
3. Secondary prevention
4. Tertiary prevention
1. Primordial prevention:
• Definition: It is the prevention of risk factors in
populations, in which they have not yet appeared .
• Interventions: The main intervention in this prevention is
through individual & mass health education.

• 2. Primary prevention: defined as action taken prior to
the onset of disease, which removes the possibility that
a disease will ever occur. It includes
• Population (mass) Strategy: It is directed at the whole
population.
• High- risk Strategy: It aims to bring preventive care to
individuals at special risk.
• 3. Secondary prevention: The action which halts the
progress of a disease at its incipient stage and prevents
complications.
• Interventions: Individual and mass case-finding
measures. Screening surveys, Selective examination

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

Dynamics of disease transmission: There are 3 link of
disease transmission:
• 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 , that it can be
transmitted to a susceptible host”.

• Reservoir:
• Types of reservoir:
1. Human reservoir
2. Animal reservoir
3. Reservoir in non living things
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”

• Cases may be:
i. Clinical cases
ii. Sub clinical cases
iii. Latent cases
• Clinical cases: Clinical illness may be mild or moderate,
typical or atypical, severe or fatal.
• 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.
• Latent infection: Infectious agent lies dormant within the
host without symptoms.

• B)Carriers: It 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:
A. According to Type:
i)Incubatory, ii)Convalescent, iii)Healthy
B. According to Duration:
i)Temporary & ii)Chronic
C. Portal of exit:
i)Urinary, ii)Intestinal, iii)Respiratory, iv)Others

A.According to 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 (recovery).
(iii) Healthy carriers: They are victims of sub
clinical infection who have developed carrier
state without suffering from disease.

B. According to 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

2. Mode of transmission:
A. Direct transmission:
1. Direct contact
2. Droplet infection
3. Contact with soil
4. Inoculation into skin or mucosa
5. Trans placental
B. Indirect transmission:
1. Vehicle borne
2. Vector borne
3. Air borne
4. Fomite borne
5. Unclean hands and fingers

• A. Direct transmission:
• Direct contact: Infection may be transmitted by direct
contact from skin to skin
• Droplet infection: This is direct projection of spray of
droplets of saliva and nasopharyngeal secretions during
coughing, sneezing, talking or spitting.
• 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
• 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
• Transplacental transmission: Disease agents can be
transmitted transplacentally. E.g. AIDS

• B. Indirect transmission:
• Vehicle borne: transmission of the infectious agent
through the water, food, raw vegetables, fruits, milk,
blood
• Vector borne: through flies, mosquitoes, cockroach,
ticks, mites, bugs, mice & rodents.
• Air borne: Droplet nuclei & Dust
• Fomite borne: Fomites are inanimate articles
contaminated by infectious agents. E.g. soiled
clothes, syringes, instruments etc.
• Unclean hands: Lack of personal hygiene causes
person- person transmission of infection.

• 3. Susceptible host:
• It includes 4 stages:
• Portal of entry: infectious agent enter the host. E.g.
Respiratory tract, alimentary tract, genito urinary
tract, skin.
• Site of election: in the body the disease agent finds
appropriate tissue for multiplication and survival.
• Portal of exit: the disease agent finds a way out of
the body.
• Survival outside: after leaving the human body the
organism must survive in the external environment
for sufficient period till a new host is found

Epidemiological Triad: The epidemiological triad is a
traditional model that explains how infectious diseases
are caused and transmitted. It's made up of three parts:

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

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

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

• Immunizing agent:
• Definitions: any substance or organism that provokes an
immune response (produces immunity) when introduced
into the body.

• Vaccination: it is a method of giving antigen to stimulate
the immune response through active immunization.
• A vaccine is an immuno-biological substance designed to
produce specific protection against a given disease.
• A vaccine is “antigenic” but not “pathogenic”.
Types of vaccines:
1. Live vaccines
2. Attenuated live vaccines
3. Inactivated (killed vaccines)
4. Toxoids
5. Polysaccharide and polypeptide (cellular fraction)
vaccines
6. Surface antigen (recombinant) vaccines.

• Immunoglobulin's:
• There are 5 major classes: IgM, IgA, IgG, IgE,
IgD
• Two types of immunoglobulin preparations:
Normal human immunoglobulin
Specific (hyper-immune) human
immunoglobulin
• Antisera or antitoxins: These are materials
prepared in animals or non human sources
such as horses.

• Immunization: A process by which a person becomes protected
against a disease through vaccination. This term is often used
interchangeably with vaccination or inoculation.
• Immunization for various diseases:
1. Measles
2. Rubella
3. Cholera
4. Pneumo & Meningococcal disease
5. Influenza
6. Diphtheria
7. Mumps
8. Tetanus
9. Hepatitis A
10. Pertussis
11. Tuberculosis
12. Hepatitis B
13. Typhoid fever
14. Hepatitis E
15. Poliomyelitis
16. Tick-borne encephalitis
17. Haemophilus influenza - b
18. Rabies
19. Varicella
20. Human papilloma-virus
21. Rotavirus gastroenteritis
22. Yellow fever
23. Japanese encephalitis
24. Malaria
25. Dengue fever

Control of infectious diseases:
• Control of infectious diseases is
reducing the transmission of disease
agent a low level that it ceases to be a
public health problem.
It includes:
I. Controlling the reservoir
II. Interruption of transmission
III. The susceptible host

Control of infectious diseases includes:
I. Controlling the reservoir:
1. Early diagnosis:
• Early diagnosis Needed for-
Treatment of patient
Epidemiological investigation
To study the time, place and person distribution.
For the institution of prevention and control measures.
2. Notification:
Once a infectious disease has been detected or
suspected is should be notified to local health
authority.

3. Epidemiological investigations:
• The outbreak investigation helps to identify:
The source of infection
Factors influencing the Spread. Include - Geographical
situations, climatic condition, social and behavioral
patterns, The character of the agent , reservoir, the
vector, vehicles & susceptible host population.
4. Isolation:
Separation of infected persons or animals from others to
prevent or limit the direct or indirect transmission of the
infectious agent from infected to susceptible.
The duration of isolation depends on communicable of
disease

5. Treatment:
To kill the infectious agent when it is still in the
reservoir before it is spread to others.
Reduce the communicability of disease.
Cut short the duration of illness
Prevent development of secondary cases
6. Quarantine:
the limitation of freedom of movement of such
well person or domestic animal exposed to
communicable disease for a period of time

II. Interruption of transmission:
Interruption of transmission Means changing some
components of man’s environment to prevent the
infective agent from a patient or carrier to susceptible
person.
E.g. simple chlorination to complex water treatment
will prevent water borne disease.
Vector control.
Personal hygiene.
III. The susceptible host:
 Immunization - providing vaccination
 Chemoprophylaxis - providing drugs to prevent the
disease

 Non specific measures:
• Mainly interrupt pathways of transmission.
• Improvements on the Quality of Life (e.g. better
housing, water supply, nutrition, education)
• Formulation of legislative measures and integrated
program.
SURVEILLANCE:
the continuous scrutiny of all aspects of
occurrence and spread of disease for effective
control.” The ultimate objective of surveillance is
“PREVENTION”.

Disinfection:
Disinfection related to control of microbial growth.
The control of microbial growth can be achieved by 2
ways
1. Killing or destroying of micro organism
2. Inhibiting the growth of micro organism
Terminologies:
• Cleaning: removing all visible duct, soils & other
foreign materials. Cleaning is necessary to reduce
the number of micro organism on environment.
• Disinfection: killing or destroying most infectious
agents.

• Sterilization: destroys all microorganisms
(include spores) on the surface of an article
or in a fluid to prevent disease transmission.
• Disinfectant: disinfectant is a substance
that inactivate or destroy microorganisms.
• Antiseptic: An antiseptic is a substance that
stops or slows down the growth of
microorganisms
• Bactericide: Agent that kills bacteria.

Methods of disinfection:
1. Natural method
2. Physical method
3. Chemical method
4. Miscellaneous
1. Natural Methods: Nature try to help in
controlling the pathogenic organism and these are
limited to domestic use.
a) Sunlight: sunlight kills many types of micro
organisms including their spores. UV rays have
effect of microbes. Linen, bedding and furniture can
be disinfected with sunlight

b) Air: Air evaporates moisture or dries the objects.
Absence of moisture causes destruction of most
micro organisms.
c) Cold: cold prevent multiplication of ordinary
bacteria and low temperature also delay the growth
of microbes. (Ex - Domestic fridge)
2. Physical methods:
i) Heat: it is most common & effective method.
Heat destroy the micro organisms.
• Heat methods may includes: dry heat ( burning,
flaming & hot air) and moist heat (boiling &
autoclave)

ii) Radiation: gamma rays, X ray used for
disinfection
3. Chemical methods: there are so many chemicals
in various forms used for disinfection.
• Commonly used chemicals are alcohol, aldehydes,
halogens, hydrogen peroxide, phenol &
ammonium.
4. Miscellaneous: some agents inhibit the growth of
organisms, some reduce the number of organisms &
some used to kill .
• Acetic acid, alkalies, dyes, filtrations, sound
vibrations & gases

1. 1st GNM Community H Nsg - Unit 4 Epidemiology.pptx

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1. 1st GNM Community H Nsg - Unit 4 Epidemiology.pptx