Epidemiology is defined as the study of health and disease in populations. It examines the patterns and causes of disease distribution. Key terms include epidemic, which is a disease rate above normal; endemic, a usual disease rate; and pandemic, a global epidemic. Epidemiology is used to study disease history, assess community health needs, estimate individual disease risk, identify disease causes, and guide prevention efforts. Prevention includes primary prevention to stop disease onset, secondary prevention to halt early disease progression, and tertiary prevention to reduce disability from established disease.

1. INTRODUCTION TO
EPIDEMIOLOGY
Nouf M. Alkusayer © 2015
1

2. Objectives
• Define Epidemiology
– Origin of the term “Epidemiology”
• Difference between: Epidemic, Endemic,
Pandemic
• Uses of Epidemiology
• Levels of prevention
1

3. “Epidemiology is primarily concerned with
identifying the important factors or variables that
influence a health outcome of interest.”1
Definition 1

4. “Epidemiology is 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 .”2
Definition 2

5. Distribution:
Terminology
Frequency or occurrence over space
and time
Disease : Absence of health
Population : Total number of people in a specific
area or having a similar characteristic

6. “Epidemiology is the study of health and disease
in a population.” 3
-The population dimension is a distinctive
characteristic of epidemiology, why?
- We tend to think of medicine dealing with health and disease
in individuals rather than population,
- Health & diseases of a population is less prominent in the
minds of most people.
Definition 3
A more general definition :

7. The basic premise of
epidemiology is…
• Disease does not occur at
random, but rather in patterns
that reflect the operation of
underlying factors.

8. Origin
Epidemiology  “epidemic”, derived
from the Greek:
Epi = on
Demos = population
Logos = discourse / study

9. What is the difference?
• epi (among) + demos = epidemic
• en (in) + demos = endemic
• pan (all) + demos = pandemic

10. What is the difference?
• Epidemic: Occurrence of disease in excess of
the expected rate. Epidemiology is the “study
of epidemics”.
• Endemic: The usual, expected rate of disease
over time.
• Pandemic: A worldwide epidemic. Epidemics
that affect several countries or continents.

11. Example of Epidemic

12. Uses of Epidemiology7
1) To study the history of disease
 Useful for studying future ‘projections’ and predictions of trends
 Useful for planning health services and public health
2) Community diagnosis
 Studying the presence, nature, and distribution of health and
disease among population. As well as the dimensions of these in
incidence, prevalence and mortality (will come back to those terms)
3) To study and assess the available health services
 Forming comparative studies between populations based on
1) The determination of needs and resources of a
population
2) Analysis of the available services
3) Finally, evaluation of the available services

13. Uses of Epidemiology7
4) To estimate the individual's chances and risks of disease.
 The estimation is based on the common experience
 The risk of individual’s risk affects risk of populations/groups
5) Completing the clinical picture
 Identification of all types of cases in proportion and their
diagnostic processes
 Cause-effect relationships are determined
 E.g. smoking frequently cause higher risk for lung cancer
6) Identify syndromes
 Establishing criteria to define syndromes
 E.g. Down syndrome, sudden death in infants, etc.

14. Uses of Epidemiology7
7) To determine the causes of health and disease
 Finding the causes can be through studying the differences of
health/disease rates between different groups
 Determination of disease sources or causes allows us to control,
prevent, eliminate disease, injury, disability, or death rates.

15. Levels of prevention3
Primary
Secondary
Tertiary

16. Levels of prevention3
Primary
The prevention of disease from occurring.
E.g. needle exchange programs to prevent the spread
of HIV, vaccination programs, smoking prevention
programs, etc.

17. Levels of prevention3
Secondary
The prevention of progression of early-staged disease
(i.e. people who carry the agent but are not symptomatic yet)
E.g. Treating asymptomatic HIV-infected patients with
antiretroviral agents to delay the onset of AIDS. Screening tests
such as for cervical cancer via Pap smears.

18. Levels of prevention3
Tertiary
The prevention of disability from
advanced/complex/long-lasting diseases and the
rehabilitation of the individual to functional capacity.
E.g. Cardiac or stroke rehabilitation programs

19. Example of the 3 levels of prevention