Infection is when an organism's body tissues are invaded by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi. It includes the multiplication of these pathogens and the response made by the host to both them, and the toxins they produce. The disease can be spread, directly or indirectly, from one person to another. Infectious diseases are sometimes called contagious disease when they are easily transmitted by contact with an infected person or their secretions, for example, common coughs, colds and flu. A contagious disease is just a type of infectious disease that is more easily transmittable.

Infectious diseases are most commonly transmitted from person to person through direct contact, such as droplets. However, infectious diseases can also easily be spread by indirect contact, such as airborne transmission, contaminated objects and surfaces, food, drinking water, contact with animals, and vector transmission such as insect bites.

The structure of a social network in an animal population significantly influences the transmission pathway and persistence of infectious diseases. For example, students on the same course or who are housemates of an infected person, are more likely to catch the disease. The aim of this experiment is to investigate how a disease might make its way through the social networks that have been created at university and how these have an effect on its dynamics and persistence.