Populations and partnerships: insights from metapopulation and pair models into the epidemiology of gonorrhoea and other sexually transmitted infections.

BACKGROUND: Models of sexually transmitted infection (STI) transmission can offer insights as to why gonorrhoea and other STIs are disproportionately concentrated in epidemiologically distinct subpopulations.
METHODS: We highlight two different constructs for modelling STIs by drawing on previously published work on pair and metapopulation models, and reanalyzed partnership data from the National Survey of Sexual Attitudes and Lifestyles II (NATSAL II) in the UK.
RESULTS: Pair models account for intrapair reinfections and are necessary to illustrate the importance of partnership dynamics. The pair modelling framework suggests that a key determinant of transmission is the length of time or 'gap' between partnerships, and that partnerships of medium length can potentially be more efficient for gonococcal transmission than the shortest partnerships. As for the metapopulation framework, one key insight is that the epidemiology of gonorrhoea is possibly being driven by subpopulations with higher than average concentrations of individuals with high sexual risk activity. The reanalysis of data on sexual behaviour in the UK shows that well recognised population subgroups at higher risk of gonorrhoea do also have higher levels of risk behaviour, such as a higher average number of new partners per year, as well as a higher prevalence of concurrent partnerships and short gaps before partnerships.
RESULTS: The concentration of risk behaviour in key population subgroups may be leading to self-sustaining pockets of transmission for STIs. Combinations of partnership behaviours at the level of population subgroups should be a subject of future empirical research as well as modelling efforts.