This document discusses the epidemiology triad and basic epidemiology. It begins with learning outcomes which are to describe the epidemiology triad, interpret the relationship between host, agent and environment, and discuss intervention concepts related to these. It then provides definitions and models of the triad and relationships between components. Specifically, it models how disease spreads under different conditions of agent strength, host susceptibility and environmental/enforcement influences. It also models intervention strategies related to the environment like housing standards and to the host like immunization and behavior modification. Overall, the document presents foundational epidemiological concepts through defining the triad components and modeling their interactions and interventions.

1. Institut
Latihan
Kementerian
Kesihatan
Malaysia
(ILKKM)
Prog
:
Diploma
in
Medical
And
Health
Science
(DPMH)
Year
1
Sem
I
MHBE 2013
BASIC EPIDEMIOLOGY ;
Epidemiology Triad
(2 Hour)

2. Learning outcome (LO) ;
1. Describe epidemiology triad.
2. Interpret the relationship between host ,
agent and environment.
3. Discuss concept of intervention related
to host , agent and environment.
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3. 1. Definition of term.
2. Model of triad.
3. Model of Relationship
between triad and prevention.
4. Model of intervention in triad.
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Content outline :

4. History epidemiology;
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John Snow (15 March 1813 – 16
June 1858) was an English
physician and a leader in the
development
of anaesthesia and
medical hygiene. He is
considered one of the founders
of modern epidemiology, in
part because of his work in
tracing the source of a cholera
outbreak in Soho, London, in
1854.
Cholera Minimata
is a neurological disease
caused by
severe mercury
poisoning. Signs and
symptoms
include ataxia, numbne
ss in the hands and
feet, general muscle
weakness, loss of
peripheral vision, and
damage
to hearing and speech.
Minamata disease
was first discovered
in Minamata city
in Kumamoto
prefecture, Japan,
in 1956

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It was caused by the release
of methylmercury in the
industrial wastewater from the Chisso
Corporation’s chemical factory, which
continued from 1932 to 1968.
thighly toxic chemical bioaccumulated and bio
magnified in shellfish and fish in Minamata
Bay and the Shiranui Sea, which, when
eaten by the local population, resulted in
mercury poisoning. While cat, dog, pig, and
human deaths continued for 36 years.
Cont’…History epidemiology;

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Simplest of these is the epidemiologic triad or triangle, the
traditional model for infectious disease.
The triad consists of an external AGENT, a susceptible HOST, and
an ENVIRONMENT that brings the host and agent together.
In this model, disease results from the interaction between the agent and
the susceptible host in an environment that supports transmission of the
agent from a source to that host
Source ; https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section8.html
Definition of term;

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Model of epid.triad;
Triad

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Cont’..Model of epid.triad;
1. AGENT;
Originally referred to an infectious 1. microorganism
or pathogen: a virus, bacterium, parasite, or other
microbe, 2. physical (eg; electrical, radiation, noises etc) ,
3. chemical (eg; L-tryptophan contaminant responsible for
eosinophilia-myalgia syndrome).
Generally, the agent must be present for disease to occur
(pahtogenicity) ; however, presence of that agent alone is not always
sufficient to cause disease.

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Cont’..Model of epid.triad;
2. HOST;
Host refers to the HUMAN who can get the
disease, also called intrinsic factor.
Opportunities for exposure are often influenced FACTORS by ;
1. behaviors such as sexual practices
2. hygiene
3. age and sex
Susceptibility and response to an agent are influenced by factors such as genetic
composition, nutritional and immunologic status, anatomic structure, presence of
disease or medications, and psychological makeup.

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Cont’..Model of epid.triad;
3. ENIVIROMENT;
Environment refers to extrinsic factors that
affect the agent and the opportunity for
exposure.
Environmental factors include ;
1. Physical factors such as geology and
climate
2. Biologic factors such as insects that
transmit the agent
3. Socioeconomic factors such as
crowding, sanitation
4. Availability of health services.

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Discuss;
where? who? why? what? how?

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Model of RELATIONSHIP ;
Stability Vs Instability

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Model of RELATIONSHIP ;
1. AGENT become infectious.
- Agent become strongest.
- Host poor immunity and sick.
- Without environment
influences.
Outcome = Disease Spread

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Model of
RELATIONSHIP ;
2. AGENT become infectious.
- Agent become strong.
- Host poor immunity and sick.
- Within environment
influences.
Outcome = Disease Spread

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Model of
RELATIONSHIP ;
3. AGENT become infectious.
- Agent not strong.
- Host highly susceptible.
- Without environment
influences.
Outcome = Disease Spread

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Model of
RELATIONSHIP ;
4. AGENT become infectious.
- Agent not strong.
- Host high susceptible.
- Within environment/
enforcement poor
influences.
Outcome = Disease Spread

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Model of
RELATIONSHIP ;
5. Stability triad.
- Agent/vectors controlled.
- Host good life style, and immunize.
- Within environment/
enforcement .
Outcome = Disease
Controlled

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Model of intervention;

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Strategies related to ENVIRONMENT include attention to
general environmental factor such as;
i. Standards of housing
ii. Nutrition
iii. Working condition
iv. Water supplies
v. Sewage disposal
vi. Control of environmental pollution
vii. Enforcement
Example ;
Prevention of transmission of food-borne infection are by hygienic
food production.
Model of
intervention;

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Strategies related to HUMAN(HOST) ;
1. include enhancement of general or specific resistance to
disease, i.e by improved nutrient or immunization.
2. Modification of personnel behaviour i.e by encouraging
people to adapt healthier lifestyles by not smoking,
avoiding obesity and exercising regularly ,etc.
3. Use of screening to detect predisposing conditions or the
early stage of disease, when action can be taken to
prevent its onset or control its progress, i.e blood
pressure to prevent hypertension or mammography for
breast cancer detection.
Model of
intervention;

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Discuss ;
Source ; https://www.thestar.com.my/lifestyle/living/2019/06/27/control-aedes-reduce-dengue

22. Student reading/ priority references :
Book / Journal / Article
No References
1. Gordis Leon (2013) Epidemiology, 5th edition,Elsevier
Suander,USA.
2. William C. Cockerham (2016) Medical sociology 13th edition,
Routledge,USA
3. Schneider.M.J(2014),Introduction to public health (4th
Edition),Jones & Bartlett Learning,USA
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Internet/ e book/ online
No References
1. http://www.moh.gov.my/
2. https://www.who.int/
3. https://books.google.com.my/books?id=AXZz6JIV9ikC&pri
ntsec=frontcover#v=onepage&q&f=false
4. https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section9.
html

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24. Recommendation for student Independent Learning (IL) ;
Activities Source
1. Search and download https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section8.h
tml
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC260
0290/
2. Reading related topic As above and,
https://www.thestar.com.my/lifestyle/living/2019/06/27/contr
ol-aedes-reduce-dengue
3. Make short note related topic As above and,
https://www.thestar.com.my/lifestyle/living/2019/06/27/contr
ol-aedes-reduce-dengue
4. Discus and answer
Exercise 1.8
https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section8.h
tml
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