In December, 2011, Science recognised the findings of the HPTN 052 study as the scientific breakthrough of the year. This study showed a 96% reduction in sexual transmission of HIV in serodifferent couples (one partner HIV positive, the other HIV negative) when the HIV-positive partner was successfully treated with antiretroviral therapy (ART). However, the HPTN 052 study included only a small number of men who have sex with men (MSM), for whom HIV acquisition often includes anal exposure, an efficient route of HIV transmission. Furthermore, the couples in the HPTN 052 study were counselled to use condoms, so the observed benefits of ART also reflected the contribution of safer sexual behaviours. Accordingly, other investigators have subsequently studied HIV transmission in couples who specifically chose not to use condoms
