Lesson 1: Introduction to Epidemiology

This is an online version of a printed textbook. It is not intended to be an online course.

Refer to the book or to the electronic PDF version (511 pages) for printable versions of text, figures, and tables.


Recently, a news story described an inner-city neighborhood’s concern about the rise in the number of children with asthma. Another story reported the revised recommendations for who should receive influenza vaccine this year. A third story discussed the extensive disease-monitoring strategies being implemented in a city recently affected by a massive hurricane. A fourth story described a finding published in a leading medical journal of an association in workers exposed to a particular chemical and an increased risk of cancer. Each of these news stories included interviews with public health officials or researchers who called themselves epidemiologists. Well, who are these epidemiologists, and what do they do? What is epidemiology? This lesson is intended to answer those questions by describing what epidemiology is, how it has evolved and how it is used today, and what some of the key methods and concepts are. The focus is on epidemiology in public health practice, that is, the kind of epidemiology that is done at health departments.


After studying this lesson and answering the questions in the exercises, you will be able to:

  • Define epidemiology
  • Summarize the historical evolution of epidemiology
  • Name some of the key uses of epidemiology
  • Identify the core epidemiology functions
  • Describe primary applications of epidemiology in public health practice
  • Specify the elements of a case definition and state the effect of changing the value of any of the elements
  • List the key features and uses of descriptive epidemiology
  • List the key features and uses of analytic epidemiology
  • List the three components of the epidemiologic triad
  • Describe the different modes of transmission of communicable disease in a population

Major Sections

Lesson 1 Overview