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HIV and other STIs spread via people's sexual connections across time and space. Transmission speed and trajectory through a population may be hastened or hindered by features of the underlying sexual network itself and the individuals who compose the network. Men who have sex with men (MSM) are disproportionately affected by STI.1 ,2 This disparity may be partly explained by three related concepts: (1) MSM networks are composed of individuals with higher behavioural risks (composition effects); (2) MSM network geometry predisposes MSM networks to higher levels of infection (network geometry) and (3) MSM demographic mixing patterns facilitate STI spread between groups (network topology). Here, we describe these three unique aspects of MSM networks and examine MSM sexual networks through a lens focused on two modern aspects of sexual partner recruitment—meeting partners during travel and through the internet and cellphone-based applications.
MSM may have worse network-level infection outcomes (ie, endemic prevalence, probability of epidemic takeoff) simply because MSM networks are composed of individuals with riskier individual-level risk factors. While numerous studies have described MSM sexual risk behaviour in isolation, the literature making direct comparisons of behaviour between MSM and exclusively heterosexual men is more limited. In two population-based surveys making this direct comparison, MSM had more recent sexual partners,2 ,3 more concurrent sexual partnerships2 and more condomless sex with two or more partners in the past year2 than heterosexual men.
MSM network geometry
Network transitivity relates to the proportion of closed triadic loops in a given network—in other words, how often are an individual's sex partners also sex partners with each other, thus forming a closed loop.4 This arrangement is impossible in exclusively …
Contributors All authors (IHS, KTB, TLG and SOA) contributed to the concepts presented. IHS wrote the first draft. All authors contributed to subsequent revisions.
Competing interests None declared.
Provenance and peer review Commissioned; externally peer reviewed.
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