1. Chapter 1
The History and Scope of Epidemiology

2. Learning Objectives
• Define the term epidemiology
• Define the components of epidemiology
(determinants, distribution, morbidity, and mortality)
• Name and describe characteristics of the epidemiologic
approach
• Discuss the importance of Hippocrates’ hypothesis and
how it differed from the common beliefs of the time
• Discuss Graunt’s contributions to biostatistics and how
they affected modern epidemiology
• Explain what is meant by the term natural
experiments, and give at least one example

3. Epidemiology Defined
• Epidemiology derives from "epidemic," a
term which provides an immediate clue to
its subject matter. Epidemiology originates
from the Greek words, epi (upon) + demos
(people) + logy (study of).

4. Definition of Epidemiology
• Epidemiology is concerned with the
distribution and determinants of health and
diseases, morbidity, injuries, disability, and
mortality in populations.
• Epidemiologic studies are applied to the
control of health problems in populations.

5. Key Aspects of This Definition
• Determinants
• Distribution
• Population
• Health phenomena
• Morbidity and mortality

6. Determinants
• Factors or events that are capable of
bringing about a change in health.

7. Examples of Determinants
– Biologic agents--bacteria
– Chemical agents--carcinogens
– Less specific factors--
stress, drinking, sedentary lifestyle, or high-fat
diet

8. The Search for Determinants
• Anthrax outbreak
• Outbreak of Fear--Ebola virus in Kikwit,
Zaire
• Fear on Seventh Ave.--Legionnaires’
disease in New York City
• Red Spots on Airline Flight Attendants--
dye from life vests
• Bioterrorism-Associated Anthrax Cases

9. Distribution
• Frequency of disease occurrence may
vary from one population group to another.

10. Disease Distribution Examples
• Hypertension more common among young
black men than among young white men.
• Coronary heart disease occurrence differs
between Hispanics and non-Hispanics.

11. Population
• Epidemiology examines disease
occurrence among population
groups, not individuals.
• Epidemiology is often referred to as
population medicine.
• The epidemiologic description indicates
variation by age
groups, time, geographic location, and
other variables.

12. Health Phenomena
• Epidemiology investigates many
different kinds of health outcomes:
– Infectious diseases
– Chronic diseases
– Disability, injury, limitation of activity
– Mortality
– Active life expectancy
– Mental illness, suicide, drug addiction

13. Morbidity and Mortality
• Morbidity--designates illness.
• Mortality--refers to deaths that occur in a
population or other group.
• Note that most measures of morbidity and
mortality are defined for specific types of
morbidity or causes of death.

14. Aims and Levels
• To describe the health status of
populations.
• To explain the etiology of disease.
• To predict the occurrence of disease.
• To control the occurrence of disease.

15. Foundations of Epidemiology
• Interdisciplinary
• Methods and procedures—quantification
• Use of special vocabulary
• Epidemic frequency of disease

16. Epidemiology Is Interdisciplinary
• Epidemiology is an interdisciplinary field
that draws from biostatistics and the social
and behavioral sciences, as well as from
the medically related fields of toxicology,
pathology, virology, genetics,
microbiology, and clinical medicine.

17. Quantification
• Quantification is a central activity of
epidemiology.
• Epidemiologic measures often require
counting the number of cases of disease.
• Disease distributions are examined
according to demographic variables such
as age, sex, and race.

18. Epidemic
• ―The occurrence in a community or region
of cases of an illness (or an outbreak)
clearly in excess of expectancy…‖
• Relative to usual frequency of the disease.

19. Infectious Disease Epidemics
• A single case of a long absent
communicable disease.
• First invasion of a communicable
disease.
• Two cases of such a disease associated
in time and place are sufficient evidence
of transmission to be considered an
epidemic.

20. Concept of Epidemic and Non-
Infectious Diseases
• Some examples that use the concept of an
epidemic are:
– Love Canal
– Brown lung disease
– Asbestosis among shipyard workers
– Diseases associated with lifestyle

21. Pandemic
• ― . . . an epidemic on a worldwide scale;
during a pandemic, large numbers of
persons may be affected and a disease
may cross international borders.‖ An
example is a flu pandemic.

22. Ascertainment of Epidemics
• Surveillance
• Epidemic threshold

23. Surveillance
• The systematic collection of data
pertaining to the occurrence of specific
diseases.
• Analysis and interpretation of these data.
• Dissemination of disease-related
information.

24. Epidemic Threshold
• The minimum number of cases (or deaths)
that would support the conclusion than an
epidemic was underway.

25. Historical Antecedents
• Environment and disease
• The Black Death
• Use of mortality counts
• Smallpox vaccination
• Use of natural experiments
• Identification of specific agents of disease
• The 1918 influenza pandemic

26. The Environment
• Hippocrates wrote On Airs, Waters, and
Places in 400 BC.
• He suggested that disease might be
associated with the physical environment.
• This represented a movement away from
supernatural explanations of disease
causation.

27. Use of Natural Experiments
• John Snow was an English physician and
anesthesiologist.
• He investigated a cholera outbreak that
occurred during the mid-19th century in
Broad Street, Golden Square, London.

28. Snow’s Contributions
• Linked the cholera epidemic to
contaminated water supplies.
• Used a spot map of cases and tabulation
of fatal attacks and deaths.

29. Snow’s Natural Experiment
• Two different water companies supplied
water from the Thames River to houses
in the same area.
• The Lambeth Company moved its
source of water to a less polluted
portion of the river.
• Snow noted that during the next cholera
outbreak those served by the Lambeth
Company had fewer cases of cholera.

30. Natural Experiment
• Definition: The epidemiologist does not
manipulate a risk factor but rather
observes the changes in an outcome as
the result of a naturally occurring
situation.

31. Contemporary Natural
Experiments
• Currently, natural experiments may be
the result of legislation, policy changes
or environmental interventions.

32. Examples of Contemporary
Natural Experiments
• Seat Belt Law--Did seat belt use reduce
fatalities from motor vehicle accidents?
• Tobacco Tax--Did the increase in cigarette
price decrease the sale of cigarettes?
• Helmet Law--Did requiring the use of
helmets by motorcyclists reduce the
number of head injuries sustained?

33. Recent Applications of
Epidemiology
• Framingham Heart Study (since 1948)
investigates coronary heart disease risk
factors.
• Smoking and lung cancer; e.g., Doll and
Peto’s study of British doctors’ smoking.
• AIDS, chemical spills, breast cancer
screening, secondhand smoke.

34. Additional Applications of
Epidemiology
• Infectious diseases
– Avian influenza
• Environmental health
• Chronic diseases
• Lifestyle and health promotion
• Psychiatric and social epidemiology
• Molecular and genetic epidemiology