Introduction to Epidemiology At the end of this session the participants will be able to: Discuss the historical evolution of epidemiology  Explain the usage of epidemiology List the core epidemiological functions  Explain types of epidemiological studies

1. INTRODUCTION TO
EPIDEMIOLOGY
By: Dr. Ismail Zubair M.D, MSc HPM

2. LEARNING OBJECTIVES
At the end of this session the participants will be able to:
 Discuss the historical evolution of epidemiology
 Explain the usage of epidemiology
 List the core epidemiological functions
 Explain types of epidemiological studies

3. EPIDEMIOLOGICAL PRINCIPLES
 Diseases (or other health events)
don’t occur at random
 Diseases (or other health events)
have causal and preventive factors
which can be identified

4. EPIDEMIOLOGY
Epi = upon
Demos = population
Logos = study of

5. HISTORY
From Hippocrate …
… To John Snow !
cholera 1854

6. Cholera 1854
investigation
CHOLERA MAP

7. JOHN SNOW PILLAR OF EPIDEMIOLOGY
 On 31 August 1854, after several other outbreaks had already occurred elsewhere in the city, a
major outbreak of cholera struck Soho. Dr. Snow later called it "the most terrible outbreak of
cholera which ever occurred in the kingdom."
 Over the next three days 127 people on or near Broad Street died
 In the next week, three quarters of the residents had fled the area
 By 10 September, 500 people had died and the mortality rate was 12.8 percent in some parts of
the city
 By the end of the outbreak 616 people died

8. JOHN SNOW AND CHOLERA
The miasmatic theory of disease held that diseases such as cholera,
Chlamydia or the Black Death were caused by a miasma (Greek
language: "pollution"), a noxious form of "bad air".

9. JOHN SNOW AND CHOLERA
 This concept has been supplanted by the germ theory of disease.
 also called the pathogenic theory of medicine, is a theory that proposes that
microorganisms are the cause of many diseases. Although highly controversial
when first proposed, it is now a cornerstone of modern medicine and clinical
microbiology, leading to such important innovations as antibiotics and hygienic
practices

10. JOHN SNOW AND CHOLERA
 In 19th century sanitory reforms was repalced by sanitory science depending
on germ theory
 Based on Epidemiology Science, Public health began to focus on preventive
measures
 By decline of the infectious disease and emmergence of the new set of
diseases related to lifestyle in the mid 20th, the profile of public health became
low...

11. DEFINITION OF EPIDEMIOLOGY
The study of the distribution and determinants of health related
states or events in specified human populations and its application to
the control of health problems
Last, 1988

12. KEY WORDS (I)
The study of the distribution and determinants of health related
states or events in specified human populations and its application to
the control of health problems.
Distribution  Time, place, person

13. KEY WORDS (II)
The study of the distribution and determinants of health
related states or events in specified human populations and its
application to the control of health problems.
Determinants  Cause, risk factors

14. KEY WORDS (III)
The study of the distribution and determinants of health related
states or events in specified human populations and its
application to the control of health problems.
Population Public health

15. KEY WORDS (IV)
The study of the distribution and determinants of health related
states or events in specified human populations and its
application to the control of health problems.
Application  Information for action

16. Epidemiology is?

17. USE OF EPIDEMIOLOGY
• Determine the magnitude and trends
• Identify the etiology or cause of disease
• Determine the mode of transmission
• Identify risk factors or susceptibility
• Determine the role of the environment
• Evaluate the impact of the control measures

18. CORE EPIDEMIOLOGIC FUNCTIONS
• Public health surveillance
• Outbreak investigations
• Data analysis
• Evaluation of disease control programs
• Communication
• Management and teamwork

19. BASIC EPIDEMIOLOGICAL APPROCH
 Observe
 Count cases (events)
 Describe
 Time, place, person
 Calculate rates,
 Compare rates
 Develop hypotheses
 Test hypotheses
 Implement actions (control, prevention)
Descriptive
Epidemiolog
y
Analytical
Epidemiology

20. DESCRIPTIVE VS. ANALYTIC
 Descriptive: Activities related to characterizing the patterns of
disease occurrence in terms of person, place or time. Hypothesis
Generating
 Analytic: Activities related to identifying possible causes for the
occurrence of disease. Hypothesis Testing

21. DESCRIPTIVE EPIDEMIOLOGY
STRENGTHS AND LIMITATIONS
 Inexpensive
 Time saving
 Describe disease patterns
 Formulate research questions
 Unable to test epidemiologic hypotheses

22. DISTRIBUTION
 How common is the disease?
 Who gets disease?
 Where does the disease occur?
 When does the disease occur?

23. DESCRIPTIVE EPIDEMIOLOGY -
PERSON
 Disease does not occur at random.
 Not all persons within a population are equally likely to develop a particular
disease.

24. DESCRIPTIVE EPIDEMIOLOGY -
PERSON
Variation of occurrence in relation to personal characteristics may reflect differences in level of:
 exposure to causal factors
 susceptibility to causal factors
 the need for some level of both susceptibility and exposure

25. DESCRIPTIVE EPIDEMIOLOGY -
PERSON
Personal characteristics that are commonly examined with respect to disease occurrence are:
 age
 race
 gender
 marital status
 education
 income
 occupation

26. DESCRIPTIVE EPIDEMIOLOGY -
PERSON
Reported cases of Tuberculosis by age in country X, in
1992

27. DISTRIBUTION
 How common is the disease?
 Who gets disease?
 Where does the disease occur?
 When does the disease occur?

28. DESCRIPTIVE EPIDEMIOLOGY -
PLACE
 Where are the disease rates highest?
 Where are the disease rates lowest?
 Does the disease rate vary by country, region, etc?

29. DISTRIBUTION
 How common is the disease?
 Who gets disease?
 Where does the disease occur?
 When does the disease occur?

30. DESCRIPTIVE EPIDEMIOLOGY - TIME
 When is the disease common?
 When is the disease rare?
 Is the frequency of the disease in the present different from
the frequency of the disease in the past?

31. DESCRIPTIVE EPIDEMIOLOGY - TIME
Reported cases of Tuberculosis by year in country X during the period
1980-1992

32. TYPES OF EPIDEMIOLOGICAL STUDIES

33. EPIDEMIOLOGY AND PREVENTION

34. Thank you