This document provides an introduction to epidemiology, including its historical development, key concepts, uses, and importance. It explores epidemiology as the study of disease distribution and determinants in populations for the purpose of disease control. The epidemiological triad of agent-host-environment is discussed as a model for explaining infectious disease transmission. The goals of epidemiology are identified as identifying disease causes and developing prevention and treatment strategies. Its importance in healthcare includes disease surveillance, screening programs, and informing public health policy and planning.

1. Introduction to Epidemiology
Unit :1
Presenter :Rukshana Ali
Department of Population Health

2. Unit Learning outcomes
At the end of the session students will be able to :
1. Analyse the historical achievements in epidemiology.
2. Explore the term epidemiology.
3. Apply the principle of epidemiological triad (agent-
host-environment) in epidemiology.
4. Determine the goals, objective and purposes of
epidemiology.
5. Explore uses and application of epidemiology in
nursing.
6. Determine the importance of epidemiology in health
care.

3. Introduction
• Many people do not know what epidemiology
is or how it contributes to the health of society.
• This fact is somewhat paradoxical given that
epidemiology pervades our lives.
• Epidemiology directly affects the daily lives of
the people.
• It affects the way that individuals make
personal decisions about their lives.
• This impacts how government , public health
department and medical organizations make
policies that affect how we live.

4. Introduction con’t
• The field of epidemiology has expanded
extremely in size , scope , and influence since
modern era,
• The number of epidemiologist have grown.
• Epidemiology training has increased in schools of
public health and medicine and nursing.
• Epidemiology is used to investigate important
public health topics.
• Many subspecialties have been established that
are define either by disease , exposure or
population being studied.

5. Historical development of
Epidemiology
• John Graunt- summarized the pattern of
mortality in 17th – century London.
• James Lind – used an experimental study to
discover the cause and prevention of scurvy.
• William Farr –developed sophisticated system
for codifying medical conditions.
• John Snow-who demonstrated that
contaminated drinking water was mode of
cholera transmission in 19th centaury.

6. Historical development of
Epidemiology con’t
• Streptomycin in Tuberculosis Trials
Committee- conducted first modern
controlled clinical trials in the 1940s.
• Framingham study -1947 has become one of
the most influential studies of heart disease.
• Doll and Hill- conducted case control studies
on smoking and lung cancer in 1950s.

7. Explore the term Epidemiology
• Epidemiology is the study of the distribution
and determinants of health-related states or
events in specified populations, and the
application of this study to the control of health
problems(Aschengrau, & Seage III,2020).
• Is the study of the distribution and
determinants of health and disease in human
populations(WHO,2017).

8. Explore the term Epidemiology
• Population –heart of all activities as
epidemiologists are concerned with disease
occurrence in group rather than individual.
• Disease frequency–how often disease arises in a
population.
• Disease distribution –who is getting the disease,
where it is occuring,and how it is changing
overtime.
• Disease determinants –factors that bring about
change in a person’s health.
• Disease control-through research

9. Goals, Objectives and Purposes of
Epidemiology
Objective
1. To identify the etiology or cause of disease.
2. To determine the extent of disease in a
population.
3. Identify the patterns and trends in disease
occurrence.
4. To study the progression of disease.
5. To evaluate preventive and therapeutic
measures for a disease or condition.

10. Goals, Objectives and purpose of
Epidemiology
Goal of epidemiology
The principal goal of epidemiology is to
identify etiological factors of disease to
encourage the most effective prevention
activities and develop treatment.

11. Goals, Objectives and Purposes of
Epidemiology
Purpose of epidemiology
When a disease occurs in a population,
epidemiologists help us to understand where
the disease is coming from, and who it is most
likely to impact.
The information gathered can then be used to
control the spread of the disease and prevent
future outbreaks.

12. Principle of epidemiological triad
• A number of models of disease
causation(relationship) have been proposed.
• Among the 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.

13. Principle of epidemiological triad
con’t
• Agent, host, and environmental factors
interrelate in a variety of complex ways to
produce disease.
• Different diseases require different balances and
interactions of these three components.
Development of appropriate, practical, and
effective public health measures to control or
prevent disease usually requires assessment of
all three components and their interactions.

14. Principle of epidemiological triad
con’t
• 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.
• The epidemiologic triad is a model for explaining
the organism causing the disease and the
conditions that allow it to reproduce and spread.

15. Epidemiologic triad

16. Agent
• Agent is the cause of the disease.
• Generally, the agent must be present for
disease to occur.
• However, presence of that agent alone is not
always sufficient to cause disease.
• The agent is the microorganism that actually
causes the disease in question.
• An agent could be some form of bacteria,
virus, fungus, or parasite.
• Agent is the ‘’WHAT ‘’of the disease

17. Host
• The agent infects the host, which is the
organism that carries the disease.
• A host doesn’t necessarily get sick.
• Hosts can act as carriers for an agent without
displaying any outward symptoms of the
disease.
• Hosts get sick or carry an agent because some
part of their physiology is hospitable or
attractive to the agent.
• Host is the “Who” of the disease

18. Environment
• The environment is the favorable surroundings
and conditions external to the host that cause or
allow the disease to be transmitted.
• The environment includes any factors that affect
the spread of the disease but are not directly a
part of the agent or the host.
• For example, the temperature in a given location
might affect an agent’s ability to thrive, as might
the quality of drinking water or the accessibility
of adequate medical facilities.
• Environment is the “where” of the disease.

19. Uses of epidemiology con’t
5. To identify syndromes by describing the
distribution and association of clinical
phenomena in the population.
6. To complete the clinical picture of chronic
diseases and describe their natural history.
7. To search for causes of health and disease by
computing the experience of groups.

20. Uses of epidemiology
1. To study the history of the health of
populations, the rise and fall of disease and
changes in their character.
2. To diagnose the health of the community and
the condition of people , incidence,
prevalence, disability and mortality.
3. To study the working of health services with
view of improvement.
4. The estimate from the group experience what
are the individual risks on average of disease,
chances of avoiding them.

21. Importance of epidemiology in health
care.
• To set policy and plan programs, public health
officials must assess the health of the population
they serve.
• Determine whether health services are available,
accessible, effective and efficient.
• Epidemiology provides data for directing public
health action.
• The information is used when planning how to
control and prevent disease in the community.

22. Importance of Epidemiology in Health
Care
Use of epidemiology in disease prevention
Primary prevention
• The effective preventative measures specific to
the stage of disease progression is also natural
history of disease.
• Primary prevention relies on epidemiological
information to indicate behaviors that are
protective , or those that will not contribute to
an increase in disease.

23. Importance of Epidemiology in Health
Care con’t
• Two types of activities constitute primary
prevention.
• First those actions that are general in nature and
designed to foster healthful lifestyles and a safe
environment (health promotion).
• Secondly actions aimed at reducing the risk of
specific diseases (specific protection)immunization.
• Epidemiological research help public health experts
to understand practices that are likely to reduce or
increase disease rates.

24. Importance of Epidemiology in Health
Care con’t
Secondary Prevention
• Occurs after pathogenesis .
• Measures are designed to detect disease at its
earliest stage.
• Namely screening and physical examinations
aim at early diagnosis.
• Epidemiological data and clinical trials
determine effective treatments and are crucial
in disease identification.

25. Importance of Epidemiology in Health
Care con’t
Tertiary Prevention
• Focuses on limitations of disability and
rehabilitation of those with irreversible
disease such as HIV.
• Epidemiological studies examine the risk
factors affecting function and suggest optimal
strategies in the care of patients with chronic
advanced disease.

26. Importance of Epidemiology in Health
Care con’t
• Helps in establishing multiple causes of disease
and help in effective prevention.
• Epidemiology aims to describe the course of
disease according to person , place and time.
• Helps in screening as this identifies risk factors and
diseases in their earlier stages, reduce those risk
factors.
• This reflects interruption in disease development in
upstream prevention for the community nurse.
• Monitoring for changes in disease
frequency(surveillance)is essential for PH
programs.

27. Importance of Epidemiology in Health
Care con’t
• Focus on the populations health care patterns.
• The accessibility and affordability of the
service.
• The barrier that may contribute to excess
morbidity in target population.
• The epidemiological study results should be
used by nurses in practice .
• It should be incorporated into prevention
programs.
• It can be used in policy making decisions.

28. Reference
Aschengrau, A., & Seage III, G. R. (2020).
Essentials of Epidemiology in Public Health
(4th ed). Burlington, USA: Jones & Bartlett
Learning.
Nies, M.A. & McEwen,M. (2019). Community/
Public Health Nursing: Promoting the
Health of Populations. (7th ed.). St Louis,
Missouri USA: Saunders Elsevier.

29. Tutorial group 1
Analyse the historical development of
epidemiology by following:
• John Graunt
• John Snow
• Richard Doll
• James Lind
• William Farr

30. Tutorial group 2
• Apply the principle of epidemiological triad
(agent-host-environment) in epidemiology
using communicable disease dengue fever.

31. Tutorial group 3
• Explore how you as a community nurse will
apply epidemiology and its uses in your
community during a outbreak of dengue fever.

32. Tutorial group 4
• Determine importance of epidemiology to you
as a community nurse.

33. Test bank
1. Analyse the historical achievements in
epidemiology.
2. Explore the term epidemiology.
3. Apply the principle of epidemiological triad
(agent-host-environment) in epidemiology.
4. Determine a goals, objective and purposes of
epidemiology.
5. Explore three uses and three application of
epidemiology in nursing.
6. Determine three importance of epidemiology in
health care.