Prevention strategies for sexually transmitted infections: importance of sexual network structure and epidemic phase.

This article explores the relationship between sexual network structure and epidemic phase in sexually transmitted disease epidemiology, and discusses how this may be used to inform prevention strategies at the population level. There are relatively few empirical studies of sexual networks, and even fewer that track the evolution of networks over time. Most studies focus on networks in the context of disease transmission and will miss the network structure in the wider population. Results from disease-related studies in the early epidemic phase show densely connected networks with multiple short loops. In later hyperendemic phases, networks appear more loosely connected with a dominance of long branching structures. The latter structure has also been described from non-diseased populations. These structures evolve over time, both of the epidemic curve and as a cohort ages and undergoes demographic change. Population strategies for prevention should vary depending on network structure and epidemic phase. In early and late epidemic phases, interventions focusing on high-risk populations--that is, dense areas of a sexual network--will have a large population effect. In contrast, for established endemic diseases a smaller change (of behaviour or interruption of transmission through screening) in a larger proportion of the population could have the largest population impact. Further empirical work on the way network structures relate to epidemic phase, and how this changes with age and social development will help to inform intervention strategies at the population level.