The PARTNER study

In the prospective observational PARTNER study serodiscordant
couples in 14 European countries in which the HIV positive
partner was on virally suppressive antiretroviral therapy and
who practised condomless sex were followed. The first part of
the study included both heterosexual and gay couples while
the second part (PARTNER2) only included gay couples. 972
serodiscordant couples were included in PARTNER2 of which
782 couples provided 1,593 couple years of follow up. Median
follow up time was 2.0 years per couple. A total of 76,088
times of condomless anal sex were reported. 15 new HIVinfections
were reported. None of these 15 infections were
linked to within-couple transmission. Zero within-couples
new HIV-infections occurred.

Ref; Rodger et al. Published online May 2, 2019 http://dx.

Comment: This study provides definite evidence that suppressive
therapy effectively prevents transmission of HIV and that
treatment as prevention works and that undetectable equals
untransmittable not only in heterosexual couples but also in
gay couples.