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보건학 개론 Introduction to Public Health
질병관리의 역학적원리
Epidemiological Principles of
Disease Control
2014
Sung-Il Cho
[[email protected]]
Graduate School of Public Health
Seoul National University
Contents
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Epidemiology: The science of epidemics
Epidemiology: Methods
Concepts of “disease control”
Infectious disease: characteristics
Infectious disease: principles of control
Chronic disease: characteristics
Chronic disease: principles of control
Conclusion
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Epidemiology
전염병?
감염병?
유행병?
• 전염병(communicable diseases)
– 감염병의 다른 말 (‘옮는’ 병) (diseases that transmit)
• 감염병(infectious diseases)
– 미생물(세균, 바이러스, 곰팡이등)이 일으키는 질병
(diseases caused by microbes)
• 유행병(epidemics)
– 통상적인 수준보다 뚜렷하게 많이 발생하는 질병
(occur beyond usual levels)
– 인플루엔자, 비만, 흡연, 자살 등도 유행병이 될 수 있다.
(include flu, obesity, smoking, suicide, … )
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Epidemiology
역학 (Epidemiology)
The Science of Epidemics
• Hippocrates’ writings: ”Of the epidemics”
• Epidemion (Greek)
= epi(upon)+demos(people)= illness among people
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Epidemiology
역학의 사전적 정의
Porta (2008): A Dictionary of Epidemiology
• 역학은 특정한 인구집단에서 건강관
련 상태나 사건의 발생과 분포를 연
구하는 학문으로서, 그러한 상태에
영향을 주는 결정요인을 탐구하고
그 지식을 건강문제 통제에 적용하
는 것을 포함한다.
• The study of the occurrence and distribution of
health-related states or events in specified
populations, including the study of the
determinants influencing such states, and the
application of this knowledge to control the
health problems.
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Epidemiology
건강관련 상태와 사건
Health-related States and Events
Event 1 Event 2
State 0
State 1
Event 3
State 2
State 3
• Measure of state occurrence: 유병률(prevalence)
– Hypertension, obesity, diabetes, disability, …
• Measure of event occurrence: 발생률 (incidence)
– Birth, death, injury, stroke, lung cancer, …
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Epidemiology
Key Measures of Occurrence:
Incidence, Prevalence, Mortality, Case fatality
• Incidence(발생률) =
Frequency of occurrence
per unit population per
unit time
• Prevalence(유병률) =
Proportion of a specific
state
• Mortality(사망률) =
Incidence of death
• Case fatality(치명률) =
Incidence of death from
a specific disease among
patients with the disease
High case fatality  high mortality
In a steady state:
Low case fatality  high prevalence
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Epidemiology
Epidemiological Methods
To Study Health-related States and Events
•
•
•
•
Measure occurrence
Describe distribution
Identify determinants (causes)
Guide application of the knowledge
to control health problems
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Disease Control
Examples of Health Problems
• Infectious diseases
• Chronic diseases
• What else?
– E.g. aging-associated functional decline
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Disease Control
WHO Family of
International Classifications
Interventions
procedures
Reasons for
encounter
IND
Nomenclature
of Diseases
Associated Products
ICD-10
International Statistical
Classification of Diseases
& Related Health
Problems
ICF
International
Classification of
Functioning, Disability
and Health
Main Classifications
Primary
care
adaptations
Speciality
adaptation
s
Adaptations
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Disease Control
ICD: An International Public Good
150 years of history
International
Standard
WHO Mortality
Database: 85 countries,
>3000 Country Years
Conversion tables
ICD 8, 9, 10
Internet Connection
On-line instructions
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Disease Control
ICF
Publications
1.
Main volume with glossary
- Full version 9999 cat.
- Short version 99 cat.
2.
Clinical Descriptions
& Assessment Guidelines
3.
Assessment Criteria
for Research
4. Other versions
-
Specialty adaptations
• Children and Youth
5.
Dedicated
Assessment Tools
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Disease Control
질병관리
(Disease control)
• Cure vs control (individual)
• Eradication vs control (population)
• Prevention vs control (e.g. CDC = Centers for
Disease Control and Prevention)
• Prevention: Actions aimed at eradicating,
eliminating, or minimizing the impact of
disease and disability (Porta: A dictionary of
epidemiology, 2008)
• Control: Ongoing operations or programs
aimed at reducing incidence and/or
prevalence, or eliminating such conditions
(Porta, 2008)
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Disease Control
Prevention & Control
• It may seem that prevention is to do
something before a disease occurs, and
control is to do something after a disease
occurs.
• However, the concepts of prevention and
control have respectively become so broad
that their ranges completely overlap
• Control = Ongoing operations and programs
for prevention
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Disease Control
Phases of Prevention
(Porta, 2008)
• 원천예방 (Primordial prevention): Minimize
hazards to health
• 1차예방 (Primary prevention): Reduce the
incidence of disease
• 2차예방 (Secondary prevention): Reduce the
prevalence of disease by shortening its duration
(early detection & treatment)
• 3차예방 (Tertiary prevention): Soften the impact of
long-term disease and disability (eliminate or
reduce impairment, disability, and handicap)
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Disease Control
Epidemiological Models
for Disease Process
• In order to implement control (ongoing
operations and programs for prevention),
we need to know the process of disease
causation and the progress.
• Epidemiological research provides the
models for disease process.
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Infectious Disease
Epidemiological Model for
Infectious Disease
숙주
병원체
질병
환경
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Infectious Disease
R Determines The Size of Epidemic
Cases
High R
Low R
R = Reproduction number(감염재생산수). Total number of cases
produced by one patient
Epidemic occurs when R >1, and ends when susceptible individuals
are depleted by death or immunity
R = scpd = (susceptible proportion)*(contact rate)
*(transmission probability)*(duration of infectivity)
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Infectious Disease
General Principles
of Infectious
Disease Control
cp
Susceptible
감수성자
1/d
Infective
감염자
Resistant
회복, 면역자
Principles:
Cases
1) Vaccination (s)
2) Prevent infection
(cp)
3) Rapid recovery (d)
patient
pool
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Infectious Disease
Control Based on The Epidemiologic
Model: Reducing the interaction
A
B
C
• A: Vaccination(s)
• Preventing infection(c, p)
– B: Stop transmission
• patients: quarantine, isolation
• susceptibles: hygiene, protection
D
E
– C: Early detection
• Surveillance & reporting
• Lab test, diagnostic confirmation
• D: Rapid recovery(d)
– Early and effect treatment
• E: Environmental control(c, p)
– Disinfection
– Biological vector control
– Physical vehicle control
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Infectious Disease
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Infectious Disease
원칙
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Chronic Disease
Top 10 Causes of Death (2010)
1. Cancer
2. Stroke
3. Heart disease
4. Suicide
5. Diabetes
6. Pneumonia
7. Low respiratory disease
8. Liver disease
9. Traffic injury
10. Hypertensive disease
How many belong to chronic disease?
What are the causes?
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Chronic Disease
Chronic Disease Process:
Multiple Causes in Multiple Steps
causes
State 0
normal
causes
State 1
obesity
State 2
hypertension
causes
...
State n
stoke
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Chronic Disease
WHO (2005)
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Chronic Disease
Quiz: With the advance of therapeutic
methods, which of the following is
expected?
1.
2.
3.
4.
Decrease in incidence
Decrease in mortality
Decrease in prevalence
Increase in prevalence
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Chronic Disease
Quiz: With the advance of therapeutic
methods, which of the following is
expected?
1.
2.
3.
4.
Decrease in incidence (prevention methods)
Decrease in mortality (therapy 1)
Decrease in prevalence (therapy 2)
Increase in prevalence (therapy 2 < therapy 1)
Prevention (Prevalence ↓)
Normal
Disease
Death
Therapy 1 (Prevalence ↑)
Therapy 2 (Prevalence ↓)
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Chronic Disease
Reducing Prevalence: Cure or Kill?
Treatment often increases prevalence
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Chronic Disease
Chronic Disease
Key Relationships
• P  PO = ID
• Prevalence approximately equals to the incidence
rate (I)  duration of the disease (D).
• PO = prevalence odds = p/(1-p)
Non-diseased
1-p
I
Diseased
1/D
Cured/Dead
p
In a steady state where p is constant, input = output.
During a fixed time, (1-p)  I = p  (1/D), i.e. p/(1-p) = PO = ID
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Chronic Disease
Chronic Disease
Characteristics and Strategies
Non-diseased
I
1-p
Diseased
1/D
Death
p
Cure?
•
•
Difficult to cure
– While cure is under research, other strategies are necessary.
– Control focuses on delaying death (reducing mortality).
– Delaying death may increase prevalence.
Long duration
– There may be time for early detection and treatment (screening).
– Control is more effective by reducing prevalence.
– Reduction of prevalence should be achieved by lowering the
incidence.
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Chronic Disease
Chronic Disease
Stopping/Slowing The Process
1-p
Non-diseased
p
I
Diseased
Pre-clinical
Clinical
Death
Tertiary
prevention
Primary prevention
Prevent disease
occurrence
1/D
Secondary prevention
Early detection &
early treatment
Treatment to
reduce disability
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Chronic Disease
Stage
Control Strategies
Risk Factors
Exposure
Disease
Prevention
Health
Promotion
1’
2’
Target
Population
All
Effect
Lower risk
Disability
3’
Risk
Factors
Limited
Ds
Advanced
Ds
Lower
incidence
Slower
progress
Lower
disability
Modified from APHA(2010)
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Chronic Disease
10 Tips
To Prevent
Cancer
(KNCC)
33
Chronic Disease
34
Chronic Disease
9 Tips To Prevent Cardiovascular Diseases
(Ministry of Health & Welfare)
35
Chronic Disease
36
Conclusions
• Epidemiology is the study of
health-related states and
events
– Occurrence, Distribution,
Determinants, Application
• Disease control is achieved
by the application of
knowledge about
determinants
• Disease control strategy can
be more effective by the use
of epidemiologic models of
disease occurrence
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