Conventional deterministic models of infection spread through populations aggregate individuals into compartments and study the dynamics of the resulting simplified system (Anderson and May 1991, Hethcote and Van Ark 1992). In this paper we explore whether knowledge of contact networks at an individual level can add to our epidemiological understanding in the particular setting of STDs. In the case of STDs the limited number and well defined nature of sexual contacts between people allows the description of the networks along which an STD can spread (Klovdahl et al. 1992, 1994). To this end a simple model describing the sexual behaviour of individuals is developed which generates sexual partner networks. The spread of a sexually transmitted disease (STD) through the population is simulated, and the characteristics of the network are related to the resultant spread of the STD. The model constructed contains many assumptions about the mechanisms controlling the sexual partnership formation behaviour, which are varied to generate a large range of possible networks. A central aim of this work is the development of the model as a tool to assist in the analysis of behavioural data. From simulations the parameters which are most influential in STD epidemiology can be identified. Samples can be taken from this network in a way which mirrors methods of sampling used in behavioural research.

The model

Individuals within the population, which can be varied in size, are treated as discrete entities with particular characteristics related to their sexual behaviour. Currently these include: sex; desired number of sexual partners per unit of time; desired duration of sexual partnerships; and a preference function for choosing sexual partners on the basis of their desired number of partners.