The hosts that are infected became the second primary object. A host lives and works in some area, where hosts are members of some demographic group, which together determine what of n types of contacts they might have to spread an infectious disease. The hosts move about the area in which they live between locations at which they interact. In EpiFlex, an area contains some configured number of locations, and locations are containers for temporary groups of hosts. Since people travel between metro areas, the model supports linkages between areas to move people randomly drawn from a configurable set of demographic groups.