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EPIDEMIOLOGY
By :
dr. Siswanto, M.Sc.
INTRODUCTION OF
EPIDEMIOLOGY
Why does a disease develop in
some people and not in others ?
The disease and health problems
are not randomly distributed in a
population.
DEFINITION
 The study of the distribution and determinants of
health related states or events in specified
populations, and the application of this to the
control of health problems.
 The study of the distribution and change in
diseases.
 The study of the distribution and determinants of
disease in human population

“Study of disease and other health related phenomena in
group of persons. (Kramer MS, 1988)

A science concerned with describing the pattern of
disease occurrence in population and determining the
factors which influence disease prevalence and
distribution with the ultimate objective of providing the
basis of control and prevention
 The characterization of the distribution of
health-related state or events is one broad
aspect of epidemiology called descriptive
epidemiology.
 Epidemiology is also used to search for
causes and other factors that influence the
occurrence of health-related state or events.
The latter is called analytic epidemiology
 Descriptive epidemiology provides the What,
Who, When and Where.
WHAT is the health problem , disease or event and what are its
manifestations and characteristics ?
WHO is affected with reference to age ,sex, social
class, ethnic, occupation, heredity and personal habits ?
WHEN does it happen, in terms of days, months, seasons or
years ?
WHERE does the problem occur, in relation to place of residence,
geographical distribution and place of exposure ?

Analytic epidemiology attempts to provide the Why,
How and So What
HOW does the health problem, disease or event occur, and what is its
association with specific conditions, agents, vectors, sources of infection,
susceptible groups and other contributing factors ?
WHY does it occur, in terms of the reasons for its persistence or
occurrence ?
SO WHAT interventions have been implemented as a result of the
information gained and what was their effectiveness ? Have there been any
improvements in health status ?
What is hospital
epidemiology?
The fundamental roles of
hospital epidemiology are to:
 Identify problem
 Identify risks
 Understand risks
 Eliminate or minimize risks
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What questions
Can be answered by
Epidemiological Approach ?
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How many peoples influenced by the
disease? Since when the disease started,
and do the number of cases tend to
increase or decrease by time?
Do the disease burdened on a specific
group of Age, gender, place, occupation,
religion, economic status groups, marriage
status, education?
What is the probable cause or risk factor
that make the disease frequency?
Which of the cause / risk factors
manageble?
What are the effective solution to control
the disease ?
Case definition is a set of
standard criteria for deciding a
person has a particular disease
(health related condition) or not
A Case definition consists of
clinical criteria include :
(symptoms/subjective
complaints, signs/objective
physical finding and laboratory
test)
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For example : in an outbreak of bloody diarrhea
caused by infection with E coli O 157:H7,
investigators defined cases in the following three
classes :
Definite case : E coli O157:H7 isolated from a
stool culture with gastrointestinal symptoms
Probable case : Bloody diarrhea with
gastrointestinal symptoms
Possible case : Diarrhea and gastrointestinal
symptoms
What kind of epidemiological
technique needed in Community Diagnosis

The Disease Frequency
measurement:
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Prevalence and Incidence rate
The trends of Prevalence &
Incidence
The distribution of prevalence or
incidence rate by age, sex,
occupation, socio-economic groups,
place, religions
Formulate Hypothesis about the risk
factors (use la londe model)
Test hypothesis
SCHEME FOR AN EPIDEMIOLOGICAL
STUDY CYCLE
DESCRIPTIVE
STUDIES
ANALYSIS OF RESULTS,
SUGGEST FURTHERDESCRIPTIVE AND NEW
HYPOTHESIS
MODEL BUILDING
FORMULATION
OF HYPOTHESIS
TEST HYPOTHESIS
ANALYTICAL STUDIES
EXPERIMENTAL STUDIES :
- X - SECTIONAL
- CASE-CONTROL STUDY
- CLINICAL TRIALS
- COHORT
- FIELD TRIALS
RESEARCH DESIGN IN EPIDEMIOLOGY
THE EPIDEMIOLOGY STUDY
OBSERVATIONAL STUDIES
(NO CONTROL OVER EXPOSURE)
EXPERIMENTAL STUDIES
(INFESTIGATOR DETERMINE)
WHO EXPOSED OR NOT EXPOSED
NO COMPARISON GROUP
COMPARISAN
GROUP
ANALYTIC
DESCRIPTIVE
CASE
SURVEILLANCE
REVIEW
SURVEY
CROS SEC
TIONAL
STUDY
CASE CON
TROL
STUDY
COHORT
STUDY
5 CRITERIA CAUSAL ASSOCIATION
1.TEMPORAL RELATIONSHIP --> means exposure to the
causal factor (risk factor) must precede development of
the disease (effect)
2. STRENGHT OF ASSOCIATION (RR> 4) --> Strength
refers to the size/magnitude of RR (not the p value or
degree of statistically significance which can be
increased by increasing the sample size).
3. CONSISTENCY (C) AND REPLICATION (R)
C--> means different studies resulted in the same
association
R--> means repetition of the same study resulted
in the same association.
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SPECIFICITY/DOSE-RESPONSE RELATIONSHIP
Measures the degree to which one particular exposure
produces one specific disease.
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COHERENCE WITH EXISTING KNOWLEDGE (BIOLOGICAL
PLAUSIBILITY)
Support for the causal of an association exist if a causal
interpretation is plausible in term of current knowledge about
the factor and the disease.
PRINCIPLES OF CAUSALITY
(SEVEN POINTS)
1.
2.
3.
4.
There should be evidence of a strong
association between the risk factor and the
disease ( Relative risk, odds ratio and
prevalence ratio)
There should be evidence that exposure to the
risk factor preceded the onset of disease
There should be a plausible biological
explanation
The association should be supported by other
investigations in different study setting
5. There should be evidence of reversibility of the
effect. ( That is, if the “cause” is removed the
“effect” should also disappear, or at least be less
likely)
6. There should be evidence of a dose response
effect.( That is, the greater the amount of
exposure to the risk factor, the greater the
chance of disease)
7. There should be no convincing alternative
explanation. ( For instance, the association
should not be explainable by confounding)
NATURAL HISTORY OF DISEASE
Natural history of disease refers to the progress of a
disease process in an individual over time, in the
absence of intervention.
The process begins with exposure to or accumulation of
factors capable of causing disease. Without medical
intervention, the process ends with recovery, disability,
or death
NATURAL HISTORY OF DISEASE
ONSET OF
SYMPTOMS
PATHOLOGIC
CHANGES
USUAL TIME
OF DIAGNOSIS
EXPOSURE
SPECTRUM OF DISEASE
STAGE OF
STAGE OF
STAGE OF
STAGE OF
SUSCEPTIBILITY SUBCLINICAL DISEASE CLINICAL DISEASE DISABILITY OR DEATH
WITHOUT MEDICAL INTERVENTION
•
•
•
RECOVERY
DISABILITY
DEATH
NATURAL HISTORY OF DISEASE
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For infectious disease, the exposure usually is
microorganism. For infectious disease the period
of subclinical is called the incubation period
For cancers, the critical factors may require both
cancer initiators, such as asbestos fibers or
components in tobacco smoke (for lung cancer)
and cancer promoters, such as estrogens (for
endometrial cancer). For chronic disease the
period of subclinical is called the latency period
DISEASES CAUSATIONS

MOSTLY MULTIFACTORIALS (> 1 factor)
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2 THEORY :
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EPIDEMIOLOGICAL TRIANGLE MODEL;
LA LONDE (Henry L Blum) MODEL.
EPIDEMIOLOGICAL TRIANGLE
MODEL
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The arising disease, is always a result of total
interaction of 3 factors:
 The Destructive power of AGENT OF DISEASE,
as an absolute factor that must be exist as the
cause.
 The Defensive Power of HUMAN HOST as the
target of agent of disease, and
 The Supporting Power of the ENVIRONMENT to
destructive power of agent of disease or to
protective power of human host
DETERMINANT OF HEALTH
EPIDEMIOLOGICAL TRIANGLE MODEL
Resistance of
Human host
against disease
Destructive power
of Agent of
diseases
Environment
AGENT OF DISEASES
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Physical agent: Temperature, dust, gas, light,
noise, radiation, etc
Chemical Agent : Acid, Base, metal, Organic
compound, food aditive, etc
Biological agent : Bactery, Insect, Allergen,
Animal’s bites, etc
Intrinsic agent : Gen, hereditary disorders;
Psychologial agent : Mental Stress;
DESTRUCTIVE POWER OF AGENT OF
DISEASE
DETERMINED BY :
 Quantity of agents;
 Duration of contact with agent of disease;
 Area of contact between agent of disease and
body of human host;
 Basic characteristic of agent of disease :
Corosive, Allergen, Toxic, Carcinogenic,
Mutagenic, Invasive, etc;
 Tissue resistance of human host against
agent of disease
HOST RESISTANCE
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Host resistance against destructive
power of agent of disease,
determined by :
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Genetic factors;
Mental & Spiritual stability
Nutritional status;
Physical fitness;
Immunity;
ENVIRONMENTAL FACTORS
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EFFECT AGAINST AGENT OF DISEASE :
 Increase /decrease number of agent of disease,
duration of contact, area of contact and destructive
power of agent of disease;
 ex High air temperature lower the body indurance
EFFECT AGAINST HUMAN RESISTANCE :
 Increase / decrease psicho-bio-physical indurance ;
 ex Food production determine the nutritional status
of population.
DETERMINANT OF HEALTH
LA LONDE MODEL
PSYCHOBIOLOGICAL
ENDURANCE
HEALTH
SERVICE
PROGRAMS
Health
problem
ENVIRONMENT
• Biological
• Social
LIFE STYLE
Three terms are used to describe an infectious
disease according to the various outcomes
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Infectivity refers to the proportion of exposed
persons who become infected.
Pathogenicity refers to the proportion of infected
persons who develop clinical disease
Virulence refers to the proportion of persons with
clinical who become severely or die
Chain of infection

Transmission of disease occur when the agent
leaves its reservoir or host through a portal of
exit, and is conveyed by some mode of
transmission, and enters through an appropriate
portal of entry to susceptible host. The process is
called the chain of infection.
RESERVOIR
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The reservoir of an agent is the habitat in which
an infectious agent normally lives, grows and
multiplies.
Reservoir include human, animal and the
environment
Two type of human reservoir

Carrier is person without apparent disease who is
capable of transmitting the agent to others.
Asymptomatic carriers , who never show
symptom during the time they are infected.
Incubatory or convalescent carriers who are
capable of transmission before or after they are
clinical ill
Two type of human resevoir

Chronic carriers is one who continues to harbor
an agent for extended time (months or years).
Exp : Hepatitis B, typhoid fever)
Symptomatic persons are usually less likely to
transmit infection widely because their symptom
increase their likelihood of being diagnosed and
treated.
Portal of exit
The path by which an agent leaves the source
host. The portal of exit usually corresponds to the
site at which the agent is localized.
Examp : tubercle bacilli and influenza virus exit
the respiratory tract, cholera vibrios in feces.
Modes of transmission
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Direct
Direct contact (kissing, sexual intercourse)
Droplet spread ( refers to spray with relative
large. Sneezing, coughing even talking)
Indirect ( an agent is carried from a reservoir to
a susceptible host by suspended air particle,
vector and vehicle)
Airborne (The nuclei less than 5 μ/micron)
Vehicleborne
Vectorborne : Mechanical, Biologic
Portal of entry
An agent enters a susceptible host through a
portal of entry.
NEW PARADIGM:
CONCEPT OF HEALTH
ILLNESSES AND
DISEASE
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HEALTH

Health is a state of individual or community’s:
physical, mental, spiritual, dan social wellbeing and
not merely a condition of free from illness and injury,
so that every individual can achieve his/her social
and economic productivity (Health Law No 23 th
1992).
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Physical, mental, spiritual dan social component of
health are inter-related one to each other, and create a
health conditions of individuals or community.
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The Integration of the 4 components of health, create
an interval scale of health states or levels of health
ranges from low health level to a perfect health level.
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COMPONENTS OF HEALTH
AND THE LEVEL OF HEALTH
PERFECT STRUCTURE AND FUNCTIONS
STRUCTURAL & FUNCTIONAL DEFECTS
PHYSICAL
MENTAL
SOCIAL
Perfect
Health
Worst
SPIRITUAL
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Consequences
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Since the doctor’s main jobs are analysing
whether her/his patients are healthy or not,
meaning that they must conclude the existing
conditions of the patient’s body & mind
structure and/or function deviate from
normality.
To be a skillfull doctors, the Medical Students
must:
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Have a good knowledge and skills in examining the
structure and functions of normal and abnormal
individuals (physically, mentally and socially);
Have a good knowledge and skills to stop the
changing process of body structures and functions
and then make it back to normal.
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WHAT THE DOCTOR’S CANDIDATE
MUST LEARN
1.
2.
The normal body and mind structure and functions
(anatomy, histology, physiology, biochemistry)
Non-normal structure and functions (microbiology,
parasitology, clinical pathology, anatomy pathology)
3.
4.
5.
Laboratory and clinical skills to practice medical
profession (Clinical Pre internship or Clerkship)
Management skills and knowledge of medical care
services (Public Health)
Intelectual skills and knowledge (Methodology, Science
Projects)
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ILLNESS VS DISEASES
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ILLNESS
One’s perception on
the signs of the
deviations /
abnormality of biopsycho-socials
structure or/and
functions of their
own or other’s
Ex. Headache,
Fever, pain, etc
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DISEASE
One’s expectations
upon causal factor/s
that stimulate the
structural and
functional deviation
of bio-psycho-social
on their own or others
Ex. HIV, Malaria, etc
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The Facts about Disease
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Every disorder/diseases must be caused by at least one
internal or external factors (mostly multifactors);
The degree of the disorders, depend on the destructive
power of the causal factors, and the protective power of
the individuals body and mentality.
There is always time lag (incubation period) between
the exposure time of factors, and the development of
sign or symptoms of diseases;
The prevention of diseases, is actually a process
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to stop the worse development of diseases, as early
as possible;
to normalize the structural and functional deviation
to achieve the highest social and economic
productivity.
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USES
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Population or community health assesment.
To do this, we must find answers to many questions :
What are the actual and potential health problems in the
community ?, Where are they ?, Who is at risk ?, Which
problems are declining over time ?, Which ones are
increasing or have the potential to increase ?, How do
these patterns relate to the level and distribution of
services available ?.
Individual decisions. People may not realize that they
use epidemiologic information in their daily decisions.
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Completing the clinical picture.
When studying a disease outbreak, epidemiologists
depend on clinical physicians and laboratory scientists
for the proper diagnosis of individual patients. But
epidemiologist also contribute to physicians,
understanding of the clinical picture and natural history
of disease.
Search for causes.
Much of epidemiologic research is devoted to a search
for causes, factors which influence one,s risk of disease.
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Health Status
For example : Prevalence, Incidence
Evaluation of intervention.
To assess the effectiveness of preventive and
therapeutic treatments.
To assess the impact of health-care services
To predict future health care needs
GOOD LUCK !
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