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Modeling versatility in sexual repertoire and HIV incidence among Peruvian gay men

The virology of HIV creates a strong transmission differential between insertive and receptive roles in all forms of sexual contact, with transmission being much more likely from an insertive HIV+ partner to a receptive HIV- partner than vice versa. This suggests that among populations of men who have sex with men (MSM), the degree of individual sexual role segregation should be an important determinant of HIV prevalence. However, this phenomenon has received little mathematical exploration, despite the fact that ethnographic research has long shown a segregation of sexual roles among MSMs in Latin American that now appears to be weakening. I present a simple deterministic model for HIV spread among MSMs that incorporates role segregation. I then use data from a survey of MSMs in Peru to explore the effect of reduced role segregation on HIV prevalence. Implications for public health interventions are discussed, as well as future refinements to the model. The latter include Bayesian melding to tune the model in the face of information about both inputs and outputs, as well as stochastic microsimulation to better incorporate heterogeneity and dependence among actor's behaviors.