This document provides an introduction to epidemiology. It defines epidemiology as the study of health-related events in populations, including how frequently diseases occur and in what patterns. The document outlines the main components of epidemiology, including descriptive epidemiology which measures disease frequency and distribution, and analytic epidemiology which aims to identify determinants and causes. It also discusses the scope, types, purposes and methods of epidemiology.

1. Introduction to
Epidemiology
By:
Hebatalla Mohamed Aly
Lecturer of industrial and occupational medicine

2. Lecture outline
• What is epidemiology
• Scope of epidemiology
• Components of epidemiology
• Types of epidemiology

3. What is epidemiology
• The word epidemiology comes from the
Greek words epi, meaning on or upon,
demos, meaning people, and logos,
meaning the study of.
• Epidemiology: is often described as the
basic science of public health.

4. What is epidemiology (cont.)
• Epidemiology is the study of the frequency,
distribution and determinants of health-
related states or events (including disease)
among specified population, and the
application of this study to the control of
diseases and other health problems.
• It is the bridge between biomedical, social and
behavioral sciences

5. What is epidemiology (cont.)
•
•Systemic collection, analysis and interpretation of data
•Includes surveillance, observations, hypothesis testing,
analytic research and experiments.
Study
•Number of times an event occur
•Number of affected/study populationFrequency
•Pattern: according to time, place and person.Distribution
•Not only causes of disease but also all factors that influence
the occurrence of disease and other health-related eventsDeterminants
•Anything that affects the health and well-being of a populationHealth related states
•Those with identifiable characteristics (community).Specified population
•Applying the knowledge gained by the studies to community-
based practice.
Application

6. What is epidemiology (cont.)
Generally epidemiology
answers 6 major questions:
how many, who, where, when,
why and how???

7. What is epidemiology (cont.)
• Frequency: answers the question of how
many?  epidemiology is a quantitative
science
• Distributions: answers the questions of who,
where and when?  epidemiology describes
health events
• Determinants: answers the questions of why
and how?  epidemiology analyzes health
events

8. What is epidemiology (cont.)
• Health related events: epidemiology not only
study diseases but any health related event
epidemiology is a broader science
• Population: epidemiology diagnose and treat
communities/populations not only patients as
clinical science epidemiology is a basic science
of public health
• Application: epidemiology have direct and
practical applications for prevention of diseases
and promotion of health epidemiology is an
applied science

9. Scope of epidemiology
• Epidemiology was originally focused exclusively
on epidemics of communicable diseases
• It was subsequently expanded to address 
endemic communicable diseases and non-
communicable infectious diseases.
• By the middle of the 20th Century, it was applied
to  chronic diseases, injuries, birth defects,
maternal-child health, occupational health, and
environmental health.
• Then epidemiologists began to look at behaviors
related to health and well-being, such as 
amount of exercise and seat belt use.

10. Types of epidemiology
• Epidemiology is classified into 2 broad
categories:
Descriptive
. Concerned with frequency
and distribution
. Answers how many, who
when and where
Analytic
. Concerned with
determinants
. Answers how and why

11. Purpose of epidemiology
1. To investigate nature / extent of health-
related phenomena in the community /
identify priorities
2. To study natural history and prognosis of
health-related problems
3. To identify causes and risk factors
4. To recommend / assist in application of /
evaluate best interventions (preventive and
therapeutic measures)
5. To provide foundation for public policy

12. Descriptive epidemiology
• Disease frequency: The core part of
epidemiology is to measure the frequency of
diseases, disability or death in a specified
population.
Ratio: is a comparison
between 2 numbers the
numerator may or mayn’t be
included in the denominator
Proportion: is a comparison
between 2 numbers but the
numerator is included in the
denominator
Rate: occurrence of an
event over time (proportion
with added dimension)

13. Descriptive epidemiology (cont.)
• Rates include:
• Assuming pop. Stable, incidence and duration
unchanged prevalence = incidence x duration
The no. of new cases of a
disease that occur during a
specified period of time in
a population at risk for
developing the disease.
Incidence
The no. of affected persons
present in the population at
a specific time divided by
the number of persons in
the population at that time:
Prevalence

14. Descriptive epidemiology (cont.)
• N.B. prevalence may be increased by:
Longer duration of disease
Prolongation of life without cure
Increase of new cases (i.e incidence)
In migration of cases
Out migration of healthy people
In migration of susceptible people
Improved diagnostic facilities

15. Descriptive epidemiology (cont.)
• Disease distribution:
Time
Place
Person

16. Time
• Changing or stable
• Disease trend over time (fluctuation)
Long term fluctuation (secular)
Periodic fluctuation (seasonal, cyclic)
Short term fluctuation (epidemic, outbreak)

17. Time
• Clustered (epidemic) or evenly distributed (endemic)
 Endemic - The habitual presence (or usual
occurrence) of a disease within a given geographic
area
 Epidemic - The occurrence of an infectious disease
clearly in excess of normal expectancy, and
generated from a common or propagated source
 Pandemic - A worldwide epidemic affecting an
exceptionally high proportion of the global
population

18. Place
• Geographically restricted or widespread
(outbreak, epidemic, pandemic)? Off-shore
(tsunami…)
• Climate effects (temperature, humidity,
combined effects..)
• Urban / sub-urban / rural
• Relation to environmental exposure (water,
food supply, etc)
• Multiple clusters or one

19. Person
• Age
• Gender
• Socio-economic status (education, occupation,
income)
• Marital status
• Ethnicity/race/genetic profile
• Behavior / habits

20. Analytic epidemiology
• Disease determinants: the questions how and
why are answered by the epidemiological
triad
Agent
environmentHost

21. Agent
• Biological agents
 Bacteria
 Viruses
 Fungi
 Parasites
• Physical agents
 Heat and cold
 Radiation
 Pressure,…
• Chemical agents
 Endogenous
 Exogenous
 Dust
 Toxic gases,..
• Mechanical agents
 Falling
 Slipping
 Hitting

22. Host
• Genetic susceptibility
• Immunologic status
• Personal characteristics (age, gender, social
class)
• Personal behavior and lifestyle
• Personal hygiene

23. Environment
• Living conditions (housing, crowding, water
supply, refuse, sewage, etc)
• Atmosphere / climate
• Mode of communication: (phenomena in the
environment that brings host and agent
together)
• Air quality