ABSTRACT
This chapter discusses some general ideas about epidemiology and a few reasons are given why students should read a book specifically about the epidemiology of infectious diseases. Most of present non-infectious disease epidemiology concerns itself with environmental and behavioural risk factors for disease. Investigations are often big and lengthy and their results may enter into public health programmes that often take years to implement. Most aspects of infectious disease epidemiology are similar to those of non-infectious disease epidemiology. The terminology, the concepts and the analysis are basically the same. Most non-infectious disease epidemiology the division between the risk factors for disease and the cases themselves is unambiguous. Smoking is a risk factor, and a patient with lung cancer is a case. Radiation is a risk factor, and a patient with leukaemia is a case. For many of the infectious diseases, someone who is a case will at the same time be a risk factor for disease in other people.
