Disease Diffusion and Epidemiology

Epidemiology is the study of how, where, and why diseases occur in populations, and geographers contribute a distinctive concern with the spatial spread, or diffusion, of disease. The most influential framework comes from the Swedish geographer Torsten Hägerstrand, whose work on spatial diffusion in the 1950s identified several distinct patterns by which phenomena, including diseases, spread across space and through populations.

Hägerstrand distinguished first between expansion diffusion and relocation diffusion. In expansion diffusion, something spreads outward from a source while remaining, and often intensifying, at the origin; the total number affected grows. In relocation diffusion, the phenomenon moves to new areas and leaves the original location behind, as when a disease travels wi