Chapter 6

Chapter 6 PRINCIPLES OF EPIDEMIOLOGY

DR. James A. Ferguson

AND

DR. D. T. Cappucci,JR.

6.1 Objective:

To provide basic principles and concepts about the science of epidemiology

6.2 Introduction

Epidemiology has been defined as the study of the distribution and determinants of diseases and health in human and animal populations.

6.3 Definitions, Derivation, and Practice

A. Epidemiology means many different things to many different people. (Many examples will be given in lecture.)`

B. It’s derivation - Epi (on, upon), demos (the people), logy (study of)

C. It’s types

1. Descriptive - Describes health and disease patterns and trends
2. Analytical - Analyzes the described variables
3. Experimental - Exposes variables to experimental design of treatment versus controlled groups or manipulates variables by means of mathematical models in computer simulations.

D. It’s phases

1. Endemic/Enzootic
2. Epidemic/Epizootic
3. Pandemic

6.4 Evolution of Epidemiology

A. 1400 B. C. - Concept of isolation and segregation/Mosaic code/Biblical dietary laws
B. 400 B. C. - Environmental versus supernatural causes for death and disease
C. 1350 A. D. - Black death and plague
D. 15th - 19th Centuries A. D. - Theories for epidemics - contagion or miasma
E. 1830 - 1860 A. D. - Environment (Great Sanitary Awakening by Chadwick, Shattuck, Snow, and others)
F. 1880 - 1890 A. D. - Agent (Bacteriology, Immunology by Koch, Pasteur, and others)
G. 20th Century A. D. - Host (Medical Ecology by NIH, Rockefeller Research Foundation, Harvard School of Public Health and others)

6.5 The Biological Balance

A. Host - Age, sex, and other parameters
B. Agent - Physical, chemical, biological
C. Environment - Physical, chemical, biological, socio-economic, and cultural

6.6 Epidemiology of Infectious Diseases

A. Definitions - Carrier, infection, incubation period, incidence, prevalence, pathogen/pathogenic, virulence
B. Chain of Infection - Source, reservoir, transmission, host entry, and new hosts
C. Source versus reservoir (= or )
D. Transmission - Direct, indirect, droplet, vector, contact, airborne, fomite
E. Entry into Host - Ingestion, venereal, contact, inhalation, inoculation, transplacental, and other
F. Control - Pasteurization, isolation, sanitation, immunization, and other

6.7. Epidemiology of Noninfectious Diseases

A. Suicide, mental health problems
B. Spousal, child, and animal abuse
C. Accidents
D. Environmental issues of chemical pollution
E. Other

6.8 Global Epidemiology

6.9 Selected Epidemics/Epizootics

6.10 Epidemic/Epizootic Investigations

A. Verify diagnosis
B. Decide whether Epidemic/epizootic exists
C. Defined by person (animal), place and time
D. Collect and analyze data
E. Formulate and test hypothesis
F. Disseminate results to public health/animal health authorities
G. Follow up with appropriate regulatory procedures as may be deemed necessary

6.11 Epidemiological Studies

A. Retrospective
B. Prospective
C. Cross-sectional
D. Longitudinal
E. Experimental (including mathematical modeling)

References

Austin, D. F. and Werner, S. B., Epidemiology for the Health Sciences. A Primer on Epidemiological Concepts and their Uses. 2nd edition. Charles C. Thomas, Springfield, IL, 1982.

Benenson, A. S., ed., Control of Communicable Diseases in Man, 15th edition. American Pubic Health Association, Washington, D. C., 1990.

Bernier, R. H. and Mason, V. M., Episource: A Guide to Resources in Epidemiology. Epidemiology Monitor, Roswell, GA, 1991.

Martin, S. W., Meek, A. H. and Willeberg, P., Veterinary Epidemiology. Principles and Methods. Iowa State University Press, Ames, 1987.

Schwabe, C. W., Veterinary Medicine and Human Health, 3rd edition. Williams and Wilkins, Baltimore, MD, 1984.

Spencer, F. J., Principles of Epidemiology. photocopied material, distributed by Centers for Disease Control, Atlanta, GA, May, 1976.

XIII. Questions

1. Define epidemiology from the standpoint of human health and veterinary medicine.

2. Discuss the evolution of epidemiology.

3. Compare and contrast infectious and noninfectious disease epidemiology.

4. List the steps in conducting an epidemiologic/epizoologic investigation.

5. Describe the various kinds of epidemiological studies.

6. Define virulence, pathogenicity, incidence, prevalence, carrier, infection, and disease.