This document provides an overview of key epidemiological concepts. It defines epidemiology as the study of disease occurrence and distribution in populations. Descriptive epidemiology describes the characteristics of disease, such as who is affected and where and when diseases occur. Analytical epidemiology searches for the causes and determinants of disease. The epidemiological triad model of disease causation includes an agent, host, and environment. The document also outlines the uses of epidemiology in public health and describes the components of the epidemiological triad.

2. PRE-REQUISITE KNOWLEDGE
 Concepts : Epidemiology, incidence & prevalence

3. LESSON OUTCOMES
At the end of this session, the student should be able to:
 Explain the difference between descriptive and analytical epidemiology
 Describe use of epidemiology
 Discuss epidemiological triad

4.  Epidemiology is the study of occurrences and distribution of diseases in
a specific population. e.g. incidence of Tuberculosis in adults aged 30
and above in Butterworth community.
 This includes the study of the determinants influencing such states and
the application of this knowledge to control the health problems.
Epidemiology

5. CONCEPTS OF EPIDEMIOLOGY
Epidemiologists study the type of a disease occurrence within a specific
population as being;
 Endemic A disease outbreak is endemic when it is consistently present
but limited to a particular region.
 An Epidemic is a sudden and great increase in the occurrence of a disease
within a population. The disease affects a large number of people in a
community or population.

6. CONCEPTS OF EPIDEMIOLOGY
 A pandemic is a rapidly emerging widespread outbreak of a disease that
affects populations across the world.

7. WHAT IS TB IN SOUTH AFRICA?

9. DESCRIPTIVE EPIDEMIOLOGY
Descriptive epidemiology describes the occurrence of a disease and
other health characteristics in the population (distribution) in
relation to ;
 Person : “The Who”, such as the age, gender, social class/
occupation affected by the diseases e.g. HIV in females aged 16-30
years
 place : “The where”, such as residence, workplace, Hospital or the
region of the people affected by the disease
 Time : ‘the when” such as the season or year the disease occurred

10. QUESTIONS SO FAR??

11. ANALYTIC EPIDEMIOLOGY
 Analytic epidemiology is concerned with the search for causes and
other factors (Determinants) that influence the occurrence of a
diseases in a population.
 It focuses on why diseases occur in a population.

12. USES OF EPIDEMIOLOGY
Epidemiology is used for the following;
 To searches for causes of diseases in a population.
 To determine the effectiveness of therapeutic and preventive measures e.g. vaccines
 To study trends over time to make predictions for the future e.g. smocking and lung cancer
 For assessing the health of the community
 For individual decisions e.g. lifestyle modification

14. EPIDEMIOLOGICAL TRIAD
 The epidemiological triangle or triad is the traditional method of infectious disease causation.
It has three components namely;
 An external agent, a susceptible host and the environment that brings the agent and the
host together

15. EPIDEMIOLOGICAL TRIAD

16. EPIDEMIOLOGICAL TRIAD
 An agent refers to the organism that cause the infectious disease. Eg viruses,
fungi, bacteria etc,
 A Host refers to the person with the disease or infection.
Factors that influence the susceptibility of the host include age, occupation or
underlying conditions and co-morbidities and travel activities.

17. EPIDEMIOLOGICAL TRIAD
 Environment refers to extrinsic factors that affect the agent and the opportunity for
exposure .
Factors include overcrowding, poor sanitation, lack of water for handwashing

18. EXAMPLES
Agent Host Environment
HIV is a viral agent that
targets the immune
system
HIV can be transmitted
when bodily fluids such
as blood come in contact
with a mucous
membrane or damaged
tissue e.g. open wound
of a human being or
during unprotected
sexual intercourse
The spread of HIV is
greatly affected by
socioeconomic factors.
These may include
poverty.
Mycobacterium
tuberculosis
Humans Overcrowding, poor
ventilation

19. EXAMPLES
Agent Host Environment
Novel coronavirus
(SARS-CoV-2)
It can potentially
transmit from human-to-
human, mainly through
respiratory droplets from
an infected
individual via coughing
or sneezing
Being in Close contact
environment
High risk work
environment e.g. COVID
-19 wards

20. SCENARIO
You are a second year student placed at Caseville Clinic and you are allocated with a
first year student. The student overheard some of your colleagues discussing
analytical and descriptive epidemiology and she did not understand.
1. Explain the difference between descriptive and analytical epidemiology to the student
so that she can understand

21. SCENARIO
 2. Describe the uses of epidemiology
 3. Name the three components of epidemiological triad

22. SUMMARY
 Epidemiology
 Types: Descriptive and analytical epidemiology
 Uses of epidemiology
 Epidemiological triad

23. SELF STUDY
 Disease determinants, Distribution, and control
 Disease surveillance: uses, processes and evaluation

24. THANK YOU

25. REFERENCES
Clark, M. 2016. Vlok's Community Health. 6th edition. Cape Town: Juta.
Enhrich & Joubert. 2014. Epidemiology. A research manual for South Africa. 3rd edition.
Cape Town: Oxford University Press