[Networks: epidemiology of transmissible diseases from a systemic perspective]

The direct or indirect physical contact between human beings as a basic condition for the transmission of infectious diseases stimulated epidemiologists to put forth great efforts to understanding and describing the process of human contacts. It is through these contacts that disease spreads over populations and emerges, at the systemic level, in the form of epidemics. During the 20th century, many researchers dedicated themselves to revealing the population patterns that favor or not the emergence of epidemics and their temporal and spatial dynamics. The first insights came from population models adapted from the physical sciences, in which non-structured populations are considered. Later on it became clear that a more detailed description of social structures was required to correctly describe epidemic dynamics, and concepts such as social group, social network and social cohesion became important terms in the quantitative study of epidemics. The approximation between epidemiology and the social sciences turns obvious as their concepts are interacting more and more. To give a brief overview of this trajectory is the purpose of this article.