MSM networks

STIsim provides two networks for modeling sexual contact between men. Both extend StructuredSexual, inheriting risk groups, concurrency, and partnership classification, but differ in how partners are matched.

Class	Matching strategy	When to use
sti.AgeMatchedMSM	Sort eligible males by age and pair sequentially	Lightweight; partners always have similar ages
sti.AgeApproxMSM	Reuses StructuredSexual age-difference preferences to match split groups of eligible males	More flexible age mixing

Participation

Both networks expose an msm_share parameter (default ss.bernoulli(p=0.015)) which sets the fraction of males that participate in MSM partnerships. Participation is assigned at sexual debut and is fixed for the lifetime of the agent.

msm = sti.AgeMatchedMSM(msm_share=ss.bernoulli(p=0.05))  # 5% of males

Combining with the heterosexual network

MSM networks are typically added alongside the default StructuredSexual network so that bisexual men contribute to transmission in both:

sim = sti.Sim(
    diseases='hiv',
    networks=[sti.StructuredSexual(), sti.AgeMatchedMSM()],
)

Each network maintains its own edges and partnership classification. Disease modules see contacts from all networks each timestep.

API

• sti.AgeMatchedMSM — exact-age matching; cheap and deterministic given inputs.
• sti.AgeApproxMSM — distribution-based matching; reuses age preference machinery from StructuredSexual.