How many HIV infections cross the bisexual bridge? An estimate from the United States

Objective: Most heterosexual women with AIDS have been infected by male sex partners who acquired HIV via injecting drug use or sex with men. The contribution of bisexuality to heterosexual HIV however, has been poorly quantified. In this paper, we estimate the number of HIV infections that spread from the homosexual community to women who have sex with bisexual men. Methods: We developed an HIV transmission model and assigned values to the model's parameters using data from a probability survey of US cities with a high risk of HIV. Results: We estimated that there are about 400 HIV infections transmitted annually from HIV-infected bisexual men in high-risk cities to their female sex partners; two-thirds of these infections are transmitted to main female partners and one-third to casual partners. Uncertainties in the value of model parameters lead to variation in expected HIV infections mostly within the range 200 to 600, and for one parameter up to nearly 800. Conclusion: We conclude that transmission via bisexuality is a relatively minor component of the estimated 40 000 annual HIV infections in the USA.