  The simplest epidemiologic model composed by mutually exclusive compartments
SIR (susceptible-infected-susceptible) is presented to describe a reality. From
health concerns to situations related with marketing, informatics or even
sociology, several are the fields that are using this epidemiological model as
a first approach to better understand a situation. In this paper, the basic
transmission model is analyzed, as well as simple tools that allows us to
extract a great deal of information about possible solutions. A set of
applications - traditional and new ones - is described to show the importance
of this model.
