The effect of antiretroviral therapy on secondary transmission of HIV among men who have sex with men

Background. Antiretroviral therapy (ART) reduces human immunodeficiency virus (HIV) RNA load and the probability of transmitting HIV to an HIV-uninfected partner. However, the potential reduction in secondary transmission associated with ART may be offset by the longer duration of infectiousness. Methods. To estimate the effects of ART on the secondary transmission of HIV among men who have sex with men, we used a previously published state-transition model of HIV disease to simulate the clinical and virologic course of HIV infection among 2 cohorts of men who have sex with men: (1) a cohort of individuals who were not receiving ART and (2) a cohort of individuals treated with US guideline-concordant ART. The model tracked the number of acts of unprotected insertive anal intercourse, transmission risk per act as determined by HIV RNA level, and the number of secondary cases generated in each cohort. Results. The estimated mean number of secondary transmissions from an HIV-infected individual after 10, 20, and 30 years of infection were 1.9, 2.5, and 2.5, respectively, in the untreated cohort, compared with 1.4, 1.8, and 2.3, respectively, in the treated cohort. The total number of transmissions for the treated cohort began to exceed the total number of transmissions for the untreated cohort 33 years after infection; over the entire course of infection, treatment with ART led to a 23% increase in secondary infections. All estimates of the impact of ART on secondary transmission were sensitive to changes in risk behaviors. Conclusions. These results suggest that ART must be accompanied by effective HIV-related risk reduction interventions. Programs that target prevention to decrease further HIV transmission are crucial to epidemic control.