• epidemiology
• sexually transmitted diseases

The recent past has brought an increased appreciation of the temporal dimension in sexually transmitted disease (STD) epidemiology and prevention science. At the individual level there is greater focus on the temporal ordering of people's sexual partnerships. Concepts like sexual trajectories, concurrency, and the gap between partnerships now attract attention as risk factors for the acquisition and transmission of STDs.^1–3 At the population level, the evolution of STD epidemics by predictable phases, characterised by changing patterns in the distribution and transmission of STD pathogens within and between subpopulations, has been a focus of recent work.^4–7 Temporal concepts in STD epidemiology have also been markedly enriched through the impact of mathematical modelling.⁸

There are important links between the temporal dimensions of individual behaviours and epidemic dynamics. The prevalence of particular sexual behaviour trajectory types, concurrent partnerships, and short gaps between partnerships within a population are increasingly considered important determinants of population prevalence and incidence of STDs, and of their rate of spread. Finally, the recent movement in epidemiology in general, towards a focus on social determinants of health conditions and on the historical evolution of those social determinants is also observable in the STD field, and contributes to increased appreciation of evolutionary frameworks.⁹ Temporal changes at both the individual and population levels will be influenced greatly by alterations in the social, demographic, cultural, and political context. For example, changes in societal parameters such as the political economy and the sociolegal system are important influences on individual patterns of sexual partnership formation and dissolution, and will also affect the nature of sexual networks within the population. In addition, these societal factors will influence other determinants of STD spread such as the availability, accessibility, and utilisation of appropriate health care, and availability and utilisation of …