Because human populations are usually large and stable, and because some types of contacts do not appear to change with population density , many models of human disease transmission will not be significantly affected by the choice of the contact–density function. But when one is interested in modelling infection dynamics in populations of different sizes or periodically fluctuating densities, the shape of the assumed contact–density function may become highly important . It is therefore not surprising that studies on how transmission rates and contacts relate to density have mainly been conducted in wildlife [10,15–19]. The main approach in these studies has been to measure disease prevalence in a field or experimental setting in which densities are manipulated or vary naturally, followed by fitting models with different transmission–density functions to the data.