ABSTRACT
This chapter deals with a number of the definitions and concepts necessary for understanding literature on infectious disease epidemiology. Most infectious diseases have such a rapid course that 'prevalence' becomes a rather uninteresting measure. National statistics on infectious diseases usually give annual incidence per 100,000 inhabitants, with the population counted at mid-year. Legionnaires' disease and tetanus are examples of diseases that are infectious but not communicable. The role played by subclinical infections and carrier states in the spread of infectious diseases constitutes an important part of modern infectious disease epidemiology and is one of the phenomena where this branch of epidemiology most clearly displays its distinctive traits. Much of routine infectious disease epidemiology relies on reports of notifiable diseases. The epidemiology of such diseases differs very little from the epidemiology of other illnesses caused by inanimate agents in the environment, such as toxins or radiation.
