HIV-1 transmission among persons with acute HIV-1 infection in Malawi: demographic, behavioral and phylogenetic relationships.

Background: Understanding of sexual networks involving acute HIV-1 infections (AHI) may lead to prevention opportunities to mitigate high rates of onward transmission. We evaluated HIV-1 phylogenetic and behavioral characteristics among persons with AHI and their referred partners.

Methods: Between 2012 and 2014, 46 persons with AHI in Malawi participated in a combined behavioral and biomedical intervention. Participants referred sexual partners for HIV-1 testing by passive referral. Demographics and sexual behaviors were collected through interviews. We used maximum-likelihood phylogenetic analyses of HIV-1 pol sequences to assess genetic relationships.

Results: Among 45 AHI participants with HIV-1 sequences, none was phylogenetically-linked with another AHI index. Nineteen (42%) AHI participants referred a single partner who returned for testing. Most referred partners (n=17) were or became HIV-infected with 15 (88%) presenting with established infection. Fourteen index-partner pairs had sequences available; 13 (93%) pairs were phylogenetically-linked dyads. The AHI index was female in 7/13 (54%) dyads. Age-disparate relationships among dyads were common (≥5-year age difference in 67% of dyads), including 3/6 dyads involving a male AHI index and a younger woman. Index participants with a referred partner were more likely to report no casual partners and to be living with their current partner than participants not in observed dyads.

Conclusions: Passive partner referral successfully identified partners with genetically similar HIV-infection - the likely source of infection - but only 40% of index cases referred partners who presented for HIV-1 testing. Future work evaluating assisted partner notification may help reach susceptible partners or more people with untreated HIV-1 infection connected to acute transmission.