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2. EPIDEMIOLOGY

3. Overview of the session
• The students are introduced to the concepts
of Epidemiology and its application in Public
Health.

4. Objectives
• At the end of the session,
the students should be able
to define epidemiology and understand the
different study designs as applied to public
health.

5. EPIDEMIOLOGY
• Study the occurrence and distribution of
diseases as well as distribution of
determinants of health state or events in
specified population and the application of
this study to control health problems
• Field of science dealing with the relationship
of the various factors which determine the
frequencies and distribution of an infectious
process. A disease or a physiological state in
human community.

6. • Study of the behavior of disease in the
community rather than in individual
patients and includes the study of
reservoirs and sources of human disease.
• Studies the patterns of disease
occurrence in human populations and
the factors that influence this pattern.
The term obviously is related to epidemic
(derived form the Greek word” upon the
people” meaning leading the people)

7. EPIDEMIOLOGY
A science concerned with the various factors
and conditions which influence the
occurrence and distribution of health,
disease, defect, disability and death among
groups of individuals.
The present usage includes studies of all
conditions and circumstances important to
man’s health.
Examples:
Accidents, Suicides, Medical care and Diseases

8. Three Major Aims of Epidemiology:
1. Construct or complete the natural history of
disease so that adequate measures for
diagnosis and treatment, and prevention can
be formulated
2. To study immediate and special problems in
the field of health. The study could provide
the necessary data upon which program may
be based; to guide the program, assessing its
progress and pinpointing failures, etc.
3. To evaluate the effectiveness of therapy,
preventive measures and programmes.

9. Epidemic- an increase in the frequency
(incidence) of a disease above the usual
and expected rate, which is called the
endemic rate., thus epidemiology count
cases of a disease, and when they detect
the sign of epidemic, they ask who, when
and where questions.
? Who is getting the disease
? Where and when the disease is occurring
? From this information, they can often make
informed guesses as to why it is occurring.

10. Notifiable disease- surveillance made
by the government before many
people start dying.
The timely reporting of cases of
notifiable disease allows public
health authorities to detect an
emerging epidemic at an early stage.
A typical Epidemiologic Investigation-
Outbreak of hepatitis

11. • It is caused by virus that contaminates food or
water, it is important to identify the source of
outbreak so that wider exposure to the virus
can be prevented.
• What are the possible questions to asked?
• Who, where and when
• Who: interviewed and asked question on
what date did the first symptoms
appear?(knowing the hepatitis A virus has an
incubation period of 30 days, it is possible to
work back on the estimated date of exposure)

12. • The where question is the hardest: where
did the victim obtain their food and water
during the period and what sources did they
have in common?
• It may be that they had eaten at the same
restaurant. The epidemiologist would visit
the restaurant and might and investigate.
They may found out that the chef had
developed Hepatitis. And was hospitalized
and so solution of the problem is easy.

13. What is the Goal of epidemiology?
The ultimate goal is to use this
knowledge to control and prevent
the spread of disease.

14. John Snow
-father of modern epidemiology
• Study about cholera – Snow would
not have been formulated his
hypothesis without the data he
gathered

15. Two Main Areas of Investigation
1. Describes the distribution of health status in
terms of age, gender, race, geography, and time.
2. Patterns of disease distribution in terms of
causal factor
• In epidemiology of any disease or event, one
studies the factor which contribute to its
causation and behavior- AGENT, HOST,
ENVIRONMENT
• Epidemiology concept maintains that there can
be no single cause of disease

16. THE AGENT FACTORS OF DISEASE
Agent is any element, substance or
force whether living or non-living
thing; the presence or absence
can initiate or perpetuate a
disease process.

17. The Epidemiologic Lever
AGENTS HOST
ENVIRONMENT

18. Types of Agent
1. This could be living or non-living
things, physical or mechanical in nature
such as extremes of temperature, light
electricity.
2. They could be chemicals- endogenous
(within the body) or exogenous
(poison)

19. Characteristics of Agent of disease
1. Inherent characteristics- physical
feature, biological requirement,
chemical composition, resistance
2. Characteristic in relation to the
environment- refers to the
reservoir and source of infection
and modes of transmission.

20. 3. Characteristic directly related to man
a. Infectivity- ability to gain access and adapt
to the human host to the extent of finding
of finding lodgement and multiplication
b. Pathogenicity- measures the ability of
agent when lodged in the body set up a
specific reaction
c. Virulence- refers to the severity of the
reaction produce and is usually measured in
terms of fatality.
d. Antigenicity- ability to stimulate the host
to produce antibody

21. Modes of Transmission
1. Direct transmission- immediate transfer of infectious
agent a receptive portal of entry
2. Indirect transmission
a. Vehicle borne- contaminated inanimate objects or
materials
b. Vector-borne- from other living organism (ex. Insects)
c. Mechanical vector
d. Biological vector
3. Airborne- dissemination of microbial aerosols to a
suitable portal of entry usually the respiratory tract
a. Droplet nuclei- usually small residues which result
from evaporation of fluid from droplets emitted by an
infected host
b. Dust

22. THE HOST FACTOR OF DISEASE
1. Age
2. Sex
3. Race
4. Habits, Customs and religions
5. Exposure to agent

23. Defense mechanism of the host
Humoral defense- these are cells in our
body like plasma cells and lymphocytes that
produce antibodies to neutralize harmful
effects of the infectious agents and body
fluids in our body that possess substance
that have antimicrobial properties
Cellular defense- there are cells in our
body like macrophages and neutrophils
involve in the process of phagocytocis

24. Immunity
This is the total property of an individual to
protect himself from an infectious agent
Two types of immunity
1. Non specific resistance- present at the
time of birth or has developed during
maturation
2. Specific resistance- acquired as a result
of prior exposure with a foreign
substance

25. Two folds of specific resistance
Active- what has been introduced to the individual
is the antigen and the body makes the antibody.
Naturally acquired active immunity- when we get
sick the infective agent will gain entry to the body,
act as stimulant for antibody formation because
the organism acts as antigen. The immunity is
lifelong (ex. Measles, chicken pox, hepatitis A)
Artificially acquired active immunity- when the
antigen has been deliberately introduce like
injecting vaccines, they act as antigen to stimulate
antibody formation. It makes use of vaccine which
is suspension of killed or living organism (ex.
MMR,OPV,BCG)

26. Passive- when what has been introduced to
the body is already antibodies that provide
immediate protection against microorganisms.
Naturally acquired passive immunity- exhibited
by the transfer of antibodies from mother’s
placenta to the fetus and transfer of antibodies
from breast milk to the baby.
Artificially acquired passive immunity- injection
of artificially prepared substance like immune
serum of gamma globulin. These two are
antibodies preparation (ex. Anti-tetanus
antibodies, diphtheria antitoxin)

27. THE ENVIRONMENTAL FACTORS OF DISEASE
Environment- sum total of an organism’s
external surrounding conditions and
influences that affect its life and development
• Physical Environment
• Climate- certain disease have seasonal
distribution
• Geography and location
• Biologic Environment- living environment of
man consist of plants, animals and fellow human
beings.
• Socio-economic environment

28. DISEASE CAUSATION
• The occurrence of disease follows biologic
laws which apply to both communicable and
non-communicable diseases.
• Disease results from imbalance between the
forces of the agent and host
• The nature and extent of imbalance depends
on the nature and characteristics of host and
agent
• The characteristics of two are influenced
considerably the condition of the
environment.

29. Incubation Period
• Time between exposure to infectious agent up to
the time of appearance of the earliest signs and
symptoms
1. Clinical incubation period- the time between
exposure to a pathogenic organism and the onset
of symptoms of a disease.
2. Biological Incubation Period- The time taken by
the parasite to complete its development in the
definite host (from the time of entry of the
infective larvae to the presence of microfilariae) is
called the Intrinsic incubation period (Biological
incubation).

30. ISOLATION AND QUARANTINE
ISOLATION
-As applied to patient, 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 effect of the direct or
indirect transmission of the infectious agent
from those infected to those who are
susceptible or who may spread the disease
agent.

31. Categories of Isolation
1. Strict isolation- this category is designed
to prevent transmission of highly
contagious or virulent infectious that
may spread by direct contact or droplet.
Includes:
• Private room, masks, gowns and gloves
for all persons entering the room
• Special ventilation requirements with a
room at negative pressure

32. 2. Contact isolation- for less highly
transmissible or serious infections, for
disease or conditions which are spread
primarily by close or direct contact.
Includes:
• Private room may share a room with the
same pathogen
• Mask for those who come close to the
patient
• Gloves are indicate for touching infectious
materials

33. 3. Respiratory isolation- to prevent
transmission of infectious diseases
over short distance through the air
Includes:
• Private room may share a room with the
same organisms of disease
• Mask for those who come close to the
patient
• Gloves and gowns are not indicated

34. 4. Tuberculosis isolation (AFB isolation)- for
patient with pulmonary tuberculosis who
have a positive sputum smear or chest x-rays
which strongly suggest active tuberculosis
Includes:
• Private room with special ventilation and the
door closed
• Mask only used only if patient is coughing
• Gowns are used to prevent gross
contamination of clothing
• Gloves are not indicated

35. 5. Enteric Precautions- for infectious
transmitted by direct or indirect
contact with feces purulent material or
drainage from an infected body site
Includes:
• Private room if the patient hygiene is
poor
• Gowns should be used if soiling is likely
• Gloves are to be used for touching
contaminated materials

36. 6. Drainage/secretion Precautions- to
prevent infections transmitted by
direct or indirect contact with purulent
material or drainage from an infected
body site.
Includes:
• Gowns should be used if soiling is likely
• Gloves are to be used for touching
contaminated materials

37. 7. Blood/body fluid Precautions- to prevent
infections that are transmitted by direct
or indirect contact with infected blood or
body fluids.
Includes:
• Private room if the patient hygiene is poor
• Gloves are to be used for touching blood
or body fluids
• Gowns should be used if soiling of
clothing with blood and body fluids is
likely

38. QUARANTINE
- restriction of the activities of a well
persons or animals who have been
exposed to a case of communicable
diseases during its period of
communicability to prevent disease
transmission during incubation of
infection should occur.

39. Categories of Quarantine
1. Absolute or Complete Quarantine
Limitation of movement of those exposed
to a communicable disease for a period
of time not longer than the longest usual
incubation period of that disease.
1. Modified Quarantine
Selective, partial limitation of freedom of
movements of contacts

40. THE DIFFERENT EPIDEMIOLOGIC
STUDIES
1. Descriptive Study
It is the description of various
epidemiological features of a
particular event.

41. 2. Analytical
• Ecological- this is also called
Correlational study. The unit of
observation is population or groups of
people rather than individual
• Cross-sectional- this measures the
prevalence of disease at a certain
point in time, and relates it with the
basis population characteristic being
surveyed such as age, sex, ethnicity,
socio-economic, etc.

42. • Case-Control- this attempt to show the
influence of a risk factor in the causation of
disease. The procedure starts with the
selection of people with a particular disease,
and the selection of people without the
disease.
• Cohort- this approach is suitable in
determining the influence of a particular risk
factor in the causation of an event, such as a
particular disease. It begins with the
identification of a group exposed to a risk
factor and a comparable group not exposed.

43. II. EXPERIMENTAL STUDY
1. Randomized Control Trial
It is an epidemiological experimental study of a new
preventative or therapeutic regimen. For this
reason, it is commonly referred to as prophylactic
trial, when testing the effectiveness of a drug to
prevent a disease, it is referred to as prophylactic
trail. Subject in a population are randomly allocated
to groups, usually called treatment and control
groups, and the results are assessed by comparing
the outcome in the two or more groups.

44. 2. Field trials
It involves people who are disease –free but presumed
to be a risk. Since the subjects are disease- free and
the purpose is to prevent the occurrence of diseases
that may occur with relatively low frequency, field
trials are often huge undertakings involving major
logistics and financial considerations.
3. Community trials
In this form of experiment the treatment groups are the
communities rather than individuals. This is
particularly appropriate for diseases that have their
origins in their social conditions, which in turns can
most easily be influenced by intervention directed at
group behavior as well as at individuals.

45. THE NATURAL HISTORY OF COMMUNICABLE DISEASE
AND THE LEVELS OF DISEASE PREVENTION
• The natural history of diseases comprises
the body of knowledge about the agent,
host and environmental factors relating to
the disease process. It includes the initial
forces/factors which initiated the process in
the environment or elsewhere through the
resulting changes which took place in man,
until continuing equilibrium is reached, or
defect, disability, or death ensues.

46. Phases
1. Pre-pathogenesis
- This is the phase before man is involved. Through
the interaction of the agent, the host and
environmental factors, the agent finally reaches
man.
- It maybe said that everyone is in the period of pre-
pathogenesis of many diseases because agents are
present in the environment where man lives
2. Pathogenesis
- This phases includes the successful invasion and
establishment of the agent in the hos

47. • After a period of incubation,
whereby the agent multiplies and
develops, or get absorbed and fix in
the tissue, sufficient tissue or
physiologic changes may have taken
place to produce detectable
evidence of the disease process in
man.

48. The Process of Infection
There are six requirements for the successful invasion
of the host by an infectious agent.
1. Condition in the environment must be favorable to
the agent or the agent must be able to adapt in
the environment
2. Suitable reservoirs must be present
3. A susceptible host must be present
4. Satisfactory portal of entry into the host
5. Accessible portal of exit from the host
6. Appropriate means of dissemination and
transmission to a new host