Discussion
HIV-1 infection, infections
HIV-1 INFECTION, INFECTIONS
We identified characteristics of likely sources of HIV-1 transmission in Zambia between 2014 and 2019. The aim of the study is to provide policy makers with data on where transmission is still occurring in a generalised epidemic in sub-Saharan Africa, despite delivery of a UTT intervention, and advise where prevention efforts should be focused.We identified men aged 25–39 years as the group most commonly transmitting HIV-1. They were the source of 43·3% of transmissions (Much prevention effort on HIV in sub-Saharan Africa has focused on intergenerational relationships, older men, and the “sugar daddy” phenomenon.11·1% and 7·0% of sources’ viral populations were dominated by variants with high-level and low-level resistance against first-line ART, respectively. A caveat is that the precise timing of ART initiation was not known, and therefore some resistance could have been acquired in sources following transmission to the recipient. Nevertheless, this level of drug resistance mirrors the high percentage of first-line ART resistance reported by other studies in the past few years.While a large majority of transmissions occurred between partners from the same community, 13·2% did not (A limitation of the This study has limitations. This work was conducted in the context of the HPTN 071 trial, which potentially limits the generalisability of results to other settings. However, the trial did have a control arm, and the only variable that we explored whose distribution showed a clear difference between arms was transmission from outside the community, which was higher in intervention arms. This is consistent with the intervention reducing transmission within-community, resulting in a larger fraction of infections being caused by introductions. Nevertheless, we acknowledge that the conditions of even the control communities might have differed from those in other locations where no trial was taking place, for example because the presence of trial staff in the community might have some effect on health-care seeking behaviour in the population.While between 13·0% and 35·2% of people living with HIV in the study communities were sampled, a proportion comparable to similar large studies in sub-Saharan Africa,HPTN 071-02 (PopART) Phylogenetics is the largest HIV phylogenetic study conducted to date, the first large transmission study to be based on an a priori power calculation, and the most comprehensive study of characteristics of sources of HIV-1 infection in sub-Saharan Africa. The study highlights that residual transmission was not limited to coming from small risk groups. However, men aged 25–39 years were, as a group, responsible for a large share of transmissions and should be prioritised in prevention efforts, even if linking them to care requires more effort.