Definition: Epidemiology is the study of the distribution and determinants of health-related states or events in populations, and the application of this study to control health problems. Methods: 1. Descriptive – Who, when, where (person, time, place) 2. Analytical – Why, how (causes, risk factors) 3. Experimental – Interventions (clinical trials, field trials) Aims: Identify the cause of disease Determine disease extent Study natural history Evaluate interventions Inform public policy Uses: Disease surveillance Health planning Risk factor identification Outcome evaluation Setting priorities Disease Transmission: 1. Direct – Person to person 2. Indirect – Through vectors, fomites, or airborne 3. Vertical – From mother to child Disease Cycle: Agent → Reservoir → Portal of Exit → Mode of Transmission → Portal of Entry → Host Spectrum of Disease: Exposure Subclinical stage Clinical disease Recovery, disability, or death Key Terms: Incidence: New cases in a time period Prevalence: All existing cases Endemic: Constant presence Epidemic: Sudden increase Pandemic: Global outbreak

1. EPIDEMIOLOGY
Prepared BY:Mehak nabi

2. • Epidemiology is the combination of the
three Greek words:
epi- among, on , upon
demos- people ,population , man
logy – study
So , epidemiology is the study of events
that occur among the people.

3. DEFINITIONS
• The study of frequency ,distribution ,and
determinants of diseases is known as
epidemiology.
OR
• Epidemiology is a philosophy , a strategy , a
methodology ,and a way of studying health
problem

4. It is the study of distribution and
determinants of health related
states or events in specified
population and the application of
this study to the prevention and
control of health problems

5. 1)Sanitary. Statistics epidemiology
2)Infectioys disease Epidemiology
3)Chronic disease epidemiology
4)Eco-Epidemiology
#concept of epidemiology

6. EPIDEMIC ( Epi- upon , demos –people)
Epidemic is an outbreak of disease in a
community in excess of normal expectation in
a given area over a particular period of time.
OR
An epidemic is a disease that affects a large
number of people within a community ,
population or region.
Some terms used in epidemiology

7. ENDEMIC ( En-in ,demos –people)
• The constant presence of disease within a
geographic area or the usual prevalence of a
given disease in a particular area.
OR
• A disease outbreak is endemic when it is
consistently present but limited to a particular
region.

8. PANDEMIC (Pan- all ,demos – people)
• An epidemic which spreads from country
to country or over the whole world.
OR
• A pandemic is a disease outbreak that
spreads across countries or continents.

9. • INCUBATION PERIOD : This is time interval between
the entry of the disease agent into the body and the
appearance of the first sign or symptom of the
disease.
• INCIDENCE : It is the number of newly diagnosed
cases of a disease occurring in a given population in
a specified time period.
• PREVALENCE : It is the total number of existing cases
of a disease in a population at a specific time.

10. • PATHOGENICITY : It is the quality or
state of being pathogenic , the potential
ability to produce disease.
• VECTOR : Usually an arthropod which
transfers an infectious agent from an
infected person to a healthy host.

11. • To describe natural history of disease
• Describe Distribution and relative importance
• Measure frequency
• To define risk groups
• To evaluate interventions
• To predict future trends and changes in disease
presentation
• Investigating health problem
• Estimate individual risk and chance towards disease
occurance
• Establishing community diagnosis
AIMS OF EPIDEMIOLOGY

12. According to International
Epidemiology Association ,
epidemiology has three main
aims:
1.To describe the distribution and
magnitude of health and disease
problem in human population.

13. 2.To identify etiological factors in
the pathogenesis of disease.
3 . To provide the data essential to
the planning , implementation
and evaluation of services for the
prevention , control and
treatment of disease.

14. • It provides time trends and disease profiles in
the population.
• It helps in planning for the medical care
facilities and for the preventive services.
• It identifies the health problems prevailing in
the community.
• It is also used for research purposes.
USES OF EPIDEMIOLOGY

15. • Epidemiology helps in determining the risk
factors and causes
• It ia used to define the various disease
syndromes ,e.g. relationship of high bp to
stroke.
• Finding the cause effect relationship is the
central point of epidemiology.
• Epidemiology provides important tools and
information for the evaluation of health
measures or programs.
• Guide health interventions to reduce
burden of disease
• Helps in shaping public health policies

16. Epidemiological
triad

21. The course of most communicable diseases is marked by certain
stages starting from entry of infection to the stage of recovery.
The stages of disease cycle are given below:
• Incubation period : This is the time interval between the entry of
the disease agent in the body and manifestation of clinical signs
and symptoms of the disease.
• Prodormal period: This is a short period ranging from 1 to 4 days
and is marked by vague signs and symptoms . Clinical diagnosis is
not possible.
DISEASE CYCLE

22. • Fastigium stage : This period represents height of the disease . Signs
and symptoms are clear –cut. The patient is confined to bed and
clinical diagnosis is possible.
• Defervescence : In this stage patient begins to feel better because the
body defenses (immunity) begin to work or respond to the pathogen.
• Convalescence : In this stage , the patient’s recovery is established .
This condition improves fast but still it may continue to be infective in
others.

23. • Defection : In the stage , the patient recovers totally from the illness but
may continue to harbor the disease agent for varying period.

24. • The term spectrum of disease is a graphical representation of the
disease . The disease in the community which occur is identical to the
spectrum of light where the colors of rainbow vary from one end to
the other but difficult to determine where one color ends and the
other begins . Similarly , in disease the one stage ends and the other
begins but difficult to pinpoint , where the one stage ends and the
other begins on the spectrum of disease.
SPECTRUM OF DISEASE

25. • One end of the spectrum is subclinical or unapparent infections which are
not ordinarily identified and on the other end is the serious illness and in
between one stage progresses to the other and so on . In the middle it may
be mild to severe. This variation in the presentation of signs and symptoms
of disease is called as spectrum of disease. It may be affected by various
factors and generally represents the immunity and receptivity level of
individual to infection.

26. SUBCLINICAL
CASES
EXTREMELY
MILD
CASES
MILD
CASES
MODERATELY
SEVERE
CASES
SEVERE
CASES
DEATH
SPECTRUM OF DISEASE

27. RESPONSIBILITIES OF
COMMUNITY HEALTH NURSE IN
EPIDEMIOLOGY-
• Maintain surveillance of the occurrence of
modifiable disease.
• Coordinates with team member during disease
outbreak.
• Participate in case finding & collection of
laboratory specimens.
• Isolation of patient having communicable
disease.
• Provide nursing care

28. • Health education
• Health teaching about disinfection.
• Prevent further spread of disease.
• Follow up case & contact.
• Supervision.
• Organize health education campaign.
• Provide Referral services
• Coordination with other sectors of
communities

29. Communicable diseases are transmitted from the
reservior or source of infection to the susceptible
host
• Source or reservior
• Mode of transmission
• Susceptible host
DISEASE
TRANSMISSION

31. It means any person,animal,arthropod,Plant,soil
and substance where
• An infectious substance lives and multiples
• Infectious substance depends primarily on its
survival
• Reproduces in order to infect the host
-RESERVIOR
Reservior can be of two types
1. Homologous Reservoir
2. Heterologous Reservoir

32. TYPES :depending on habitat
1. Human Reservoir
2. Animal Reservoir
3. Non living thing Reservoir

33. HUMAN RESERVOIR
1) Cases
• Clinical cases
• Sub clinical cases
• Latent cases
2)Carriers
Types depending on time period when infectious agent
shedding take place
• Incubatory carrier
• Convalescent carrier
• Healthy carriers

34. Depending on duration of shedding
of infectious agent
• Temporary carriers
• Chronic carriers
Depending on portal of exit
• Urinary
• Intestinal
• Respiratory
• Others

35. • The route by which infectious agent is transmitted from reservoir
to another host is called mode of transmission or disease
transmission.
• The place where the infectious agent usually lives before infecting
a new host is known as reservoir.
• Mode of transmission can be classified into:
1. Direct transmission
2. Indirect transmission
-DISEASE
TRANSMISSION

36. DIRECT
TRANSMISSION
• In this infectious agent is directly transmitted to
a new host. This does not require the help of
intermediates like food , air, water or animals.
• Generally speaking the direct transmission can
occur from person to person through many
ways and transplacental i.e., from pregnant
mother to fetus.

37. More specifically direct transmission is
classified into five:
• DIRECT CONTACT
• DROPLET INFECTION
• CONTACT WITH SOIL
• INOCULATION INTO SKIN OR MUCOSA
• TRANSPLACENTAL

38. • DIRECT CONTACT :The susceptible host gets the
infection directly from source of infection through
direct contact like skin to skin , mucosa to mucosa ,
mucosa to skin.
e.g. , STD’s ,AIDS
• DROPLET INFECTION : Transmission of infection
takes place through direct spray of droplets of saliva
and secretions while coughing sneezing , speaking or
spitting.
e.g,Tuberculosis , common cold

39. • CONTACT WITH SOIL :The disease agent is directly
acquired from the soil by the susceptible tissue of the host
when it comes in contact with it.
e.g, tetanus, mycosis.
• INOCULATION INTO SKIN OR MUCOSA :in this the
disease agent may be inoculated directly into the skin or
mucosa .
e.g, rabies
• TRANSPLACENTAL OR VERTICAL : This refers to the
transmission of an infectious agent from a pregnant mother to
her fetus through the placenta.

40. INDIRECT
TRANSMISSIO
N
• Infectious agents are transmitted to new hosts through
intermediates such as air , water , food etc. Five ‘Fs’ are playing are
playing an important role – they are: FLIES, FINGERS ,
FOMITES ,FOOD and FLUID.
• Indirect transmission includes:
a)Vehicle borne
b)Vector borne
c) Air borne
d) Fomite borne
e) Unclean hands and fingers

41. VEHICLE BORNE : This involves transmission of the
agent through water , food ,blood , serum and
biological products.
VECTOR BORNE : Vector is defined as an arthropod
, or any living carrier that transports an infectious
agent to a susceptible individual via biting, scratching
, body fluids

42. Vectorn borne transmission consists in
connection to vector and spread
1)Mechanical vector borne
2)Mechanical vector borne

43.  AIR BORNE : This involves transmission of infected agent through air .it
includes –droplet nuclei and dust
• Droplet nuclei are the particles concerned in the spread of airborne
infection . These tiny particles are formed from dried remains of droplet .
They may be formed by evaporation of droplets coughed or sneezed ,
generated decisively by atomizing devices .
• Dust are larger particles discharged while talking , coughing and sneezing
settle out on carpets , furniture , clothes , bedding etc. During dusting ,
sweeping , bed making the agents become part of air.

44.  FOMITE BORNE : fomites are defined as inanimate articles or
substance ( other than water or food) , contaminated by the
infectious discharges from a patient and capable of harboring and
transferring agents to a healthy person.e.g, soiled
clothes ,towel,pen,pencil
 FINGERS AND HANDS: Fingers and hands are the very common
agents for transmitting infections . Hands and fingers act as media
of transfer of disease producing agents to food.i.e, poor sanitation,
hygiene and lack of cleanliness

45. An individual who does not have sufficient immunity
against a particular infectious agent to prevent contracting
an infection when exposed to an infectious agent is
termed as susceptible host. A susceptible host must be
exposed to an infectious agent or infected source in a way
that can enable the acquisition of an infection
_
-SUSCEPTIBLE
HOST

46. Susceptibility of the host determines the transmission of
disease agents. String of events that occur in the host
include:
Portal of entry: There are various ways through which
the agent can enter the host like respiratory tract,
alimentary canal, genitourinary tract, skin, etc. Some
organisms may have quite a few ways of entry.
Site selection: After entering into a host, the organism
looks for suitable site or tissue for development and
survival.

47. Portal of exit: The agent must find a way out
of the body and reach a new host. If there is no way
out, the infection becomes dead end infection.
Survival of organism: The disease causing
agent survive in the external environment till it
finds a new host.

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