ABSTRACT
This chapter addresses the concept of contact patterns in more depth. It describes methods to depict such patterns and provides some examples of the research methods, which used to investigate how people mix. The epidemiology of infectious diseases is not only about the properties of various pathogens and their hosts but also to a great extent and issue of contact patterns in the population. For sexually transmitted infections contacts between a case and a new partner may be far between, and these infections thus have to have a very long period of infectivity, often in the order of months or years. The probability of a contact outside the group during the infectious period must have been low. Sociologists often make use of graphs to describe the network of contacts in a group of people. For many infectious diseases, population density and subsequently contact density thus become important determinants of epidemiology.
