1. Basic Epidemiological concepts
Dr.Haitham Issa Al – Banna
Assistant professor
Hawler college of Medicine

2. EPIDEMIOLOGY
Greek: EPI - Upon DEMOS - People LOGOS - Study of, Body of Knowledge

3. History of Epidemiology

4. Hippocrates (460-377 B.C.) On Airs, Waters, and Places
Idea that disease might be associated with physical environment

5. Edward Jenner ( )
Pioneered clinical trials for vaccination to control spread of smallpox 
Jenner's work influenced many others, including Louis Pasteur who developed vaccines against rabies and other infectious diseases

6. Ignas Semmelweis (1840’s)
Pioneered handwashing to help prevent the spread of septic infections in mothers following birth 

7. John Snow (1813-1858) Father of epidemiology
Careful mapping of cholera cases in East London during cholera epidemic of 1854
Traced source to a single well on Broad Street that had been contaminated by sewage

9. Why is epidemiology the basic science of public health?
PUBLIC HEALTH WORKS BY:
• Defining a health problem
• Identifying risk factors associated with the problem
• Developing and testing community-level interventions to control or prevent the causes of the problem
• Implementing interventions to improve the health of the population; and
• Monitoring those interventions to assess their effectiveness

10. DEFINITIONS OF PUBLIC HEALTH
• The science and art of :
1) preventing disease
2) prolonging life and
3) promoting health and efficiency
through organized community effort.

11. Epidemiology asks or uses:
Person- Who?
Place- Where?
Time- When?
Helps us to understand: Why?

12. Definition of epidemiology
The study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control of health problems.

13. Introduction to Epidemiology Key words
Study
Distribution
Determinants
Health-related states
Populations
Application

14. Epidemiology key words: Study
Epidemiology is the basic science of public health.
It's a highly based on principles of statistics and research methodologies.

15. Epidemiology key words: Distribution
Epidemiologists study the distribution of frequencies and patterns of health events within groups in a population.
They use descriptive epidemiology, which characterizes health events in terms of time, place, and person.
Questions: who, where, when

16. Epidemiology key words: Determinants
Epidemiologists also attempt to search for causes or factors that are associated with increased risk or probability of disease.
What factors cause the problem or are associated with the problem
Questions: how and why

17. Epidemiology key words: Health-related states
Epidemiology is applied to the whole spectrum of health-related events:
chronic diseases,
environmental problems,
behavioral problems,
injuries,
infectious diseases.

18. Epidemiology key words: Populations
One of the most important distinguishing characteristics of epidemiology is that it deals with groups of people rather than with individual patients.

19. Epidemiology key words: Application.
Epidemiological data aids in developing and evaluating interventions to control and prevent health problems.

20. Clinician Epidemiologist
Patient’s Community
Diagnosis Predict trend
Therapy Control
Cure Prevention

21. Objectives of epidemiology (uses of epidemiology)
1- Assessment of the health situation
Collect basic data about diseases and health-related problems in the community
2- Study natural history and etiology of disease
Help understand risk factors and natural history of disease
3- Control and prevention
Provide recommendations for control and prevention of health problems in the population

22. 4- Planning health interventions
Provide data for developing health policy and sound planning
5- Evaluation of health interventions
Assess the impact of health programs and interventions

23. Kinds of Epidemiology
Descriptive
Analytic

24. The Basic Triad Of Descriptive Epidemiology
THE THREE ESSENTIAL CHARACTERISTICS OF DISEASE WE LOOK FOR IN DESCRIPTIVE EPIDEMIOLOGY:
TIME
PLACE
PERSON

25. Descriptive Epidemiology
Study of the occurrence and distribution of disease
Terms:
Time
Place
Person

26. Time Changing or stable? Seasonal variation.
Clustered (epidemic) or evenly distributed (endemic)?
Point source or propagated.

27. Time
Secular
Periodic
Seasonal
Epidemic

28. Secular Trend
The long-time trend of disease occurrence

29. Tetanus – by year, United States, 1955-2000
During 2000, a total of 35 cases of tetanus were reported. The percentage of cases among persons aged years
Has increased in the last decade. Note: A tetanus vaccine was first available in 1933.
Reported Cases

30. 4. Disease incubation period
Epidemic curve
A graph of the time distribution of epidemic cases.
An epid. Curve can suggest:
1- Time trend
A time relationship with exposure to a suspected source.
2- Pattern of spread:
A cyclical or seasonal pattern suggestive of a particular infection, and common source or propagated spread of the disease.
3. Magnitude
4. Disease incubation period

31. Periodic Trend
Temporal interruption of the general trend of secular variation

32. Whooping Cough - Four-monthly admissions, 1954-1973

33. Seasonal Trend

34. 4. Disease incubation period
Epidemic curve
A graph of the time distribution of epidemic cases.
An epid. Curve can suggest:
1- Time trend
A time relationship with exposure to a suspected source.
2- Pattern of spread:
A cyclical or seasonal pattern suggestive of a particular infection, and common source or propagated spread of the disease.
3. Magnitude
4. Disease incubation period

35. Epidemic
An increase in incidence above the expected in a defined geographic area within a defined time period

36. Endemic vs. Epidemic
No. of Cases of a Disease
Epidemic
Endemic
Time

37. Place Geographically restricted or widespread (pandemic)?
Relation to water or food supply.  
Multiple clusters or one?

38. Place
Where patient was exposed or
Where source became infected

40. Person
Age
Socio-economic status
Gender
Ethnicity/Race
Behavior

41. Analytic Epidemiology
Further studies to determine the validity of a hypothesis concerning the occurrence of disease.

42. The Basic Triad Of Analytic Epidemiology
THE THREE PHENOMENA ASSESSED IN ANALYTIC EPIDEMIOLOGY ARE:
HOST
Define host, agent?
AGENT
ENVIRONMENT

43. Agents Nutrients Poisons Allergens Radiation Physical trauma Microbes
Psychological experiences

44. Host Factors Genetic susceptiblity Immunologic state Age
Personal behavior

45. Environment Crowding Atmosphere
Modes of communication – phenomena in the environment that bring host and agent together, such as:
Vector
Vehicle
Reservoir

46. Other different important
definitions

47. Incidence
Measure of new cases of disease (or other events of interest) that develop in a population during a specified period of time
E.g. Annual incidence
Measure of the probability that unaffected persons will develop the disease
Used when examining an outbreak of a health problem

48. Prevalence Number of existing cases of disease or other condition
Proportion of individuals in a population with disease or condition at a specific point of time
Diabetes prevalence, smoking prevalence
Provides an idea of how severe a problem may be – measures overall extent
Useful for planning health services (facilities, staff)

50. Relationship Between Incidence and Prevalence
Prevalence varies directly with both incidence and duration.
If incidence is low, but duration is long (chronic), prevalence will be large in relation to incidence.
If prevalence is low because of short duration (due to recovery, migration or death), prevalence will be small in relation to incidence.

51. Morbidity – illnesses, symptoms, impairments
Mortality - deaths
Acute disease – diseases that strike and disappear quickly, within a month or so (chicken pox, colds)
Chronic disease – long term or lifelong diseases, incurable

52. Epidemiologic Measures

53. Tools
Count
العدد
Rate
المعدل
Proportion
التناسب
Ratio
النسبة

54. Count العدد

55. Why is a simple count not enough?
3 cases of cancer per year from a city of 1,000 people is very different than 3 cases per year from a city of 100,000 people

56. So, in epidemiology we must know:
the size of the population from which the affected individuals come, and
the time period the information was collected.

59. Example of proportion:

60. RATIO
A fraction in which the numerator is not part of the denominator.
e.g. Fetal death ratio: Fetal deaths/live births.
Fetal deaths are not included among live births, by definition.

61. Ratio & Proportion
Female
All
Female
Male
Ratio
Proportion

63. Maternal mortality ratio- Number of maternal deaths ascribed to childbirth. Reflects health care access
Number of deaths
assigned causes related to
child birth
maternal = x 100,000 live births
mortality ratio Number of live births

64. Rate Special form of proportion that includes a specification of time
Most commonly used in epidemiology because it most clearly expresses probability or risk of disease or other events in a defined population over a specified period of time
2 major types
Crude rates
Specific rates (age-specific, infant mortality)

65. Rate The basic formula for a rate is as follows:
Number of cases or events occurring
during a given time period
Rate =
Population at Risk during the same time period X

68. Epidemic investigation
Rule of six: Max. 6 words in a line and 6 lines/slide

69. Endemic vs. Epidemic
No. of Cases of a Disease
Epidemic
Endemic
Time

70. Outbreak Detection and Response
First
Case
Detection/
Reporting
Lab
Confirmation
Response
DAY
CASES
Opportunity
for control

71. Outbreak Detection and Response
First
Case
Detection/
Reporting
Confirmation
Investigation
Opportunity
for control
Response
DAY
CASES

72. objectives of an epidemic investigation
1- To define the magnitude of the epidemic in terms of time, place and person.
2- To determine the particular factors responsible for the occurrence of the epidemic.
3- To identify the cause, source(s) of infection, and modes of transmission to determine measures necessary to control the epidemic.
4-To make recommendations to prevent recurrence.
Rule of six: Max. 6 words in a line and 6 lines/slide

76. The elements of epidemic control include:
1. Controlling the source of the pathogen (if known) Remove or inactivate the pathogen
2. Interrupting the transmission Sterilize environmental source of spread and vector control
3. Controlling or modifying the host response to exposure, Immunize the susceptible; use prophylactic chemotherapy