February 13–16, 2017

Conference Dates and Location: 
February 23-26, 2015 | Seattle, Washington
Abstract Number: 

HIV Transmission in Male Serodiscordant Couples in Australia, Thailand and Brazil


Andrew E. Grulich1, Benjamin R. Bavinton1, Fengyi Jin1, Garrett Prestage1, Iryna B. Zablotska1, Beatriz Grinsztejn2, Nittaya Phanuphak3, Richard Moore4, Kersten K. Koelsch1
1 Kirby Institute, University of New South Wales, Sydney, NSW, Australia. 2 Instituto de Pesquisa Clínica Evandro Chagas, Rio de Janiero, Rio de Janiero, Brazil. 3 Thai Red Cross AIDS Research Centre, Bangkok, Thailand. 4 Northside Clinic, Melbourne, VIC, Australia.

Abstract Body: 

Background: Numerous prospective studies have demonstrated that HIV transmission is greatly reduced in heterosexual HIV serodiscordant couples when the HIV-positive partner (HPP) is receiving combination anti-retroviral therapy (cART) with undetectable viral load (UVL). Comparable data in homosexual male serodiscordant couples (HM-SDC) are extremely limited. We report a pre-specified interim analysis of the relationship between UVL and HIV transmission in the Opposites Attract observational cohort study of HM-SDC in Australia, Bangkok and Rio de Janeiro.

Methods: HM-SDC reporting regular anal intercourse with each other were recruited through clinical sites. Detailed information on sexual risk behaviours was collected at each visit from the HIV-negative partner (HNP). HNPs were tested at baseline and follow-up for HIV antibodies and STIs (sexually transmitted infections), and HPPs for HIV viral load and STIs. Incidence rates were calculated per couple-year of follow-up (CYFU) using person-year methods, and stratified by whether different forms of condomless anal intercourse (CLAI) were reported. UVL was defined as <200 copies/mL. One-sided confidence intervals (CI) were calculated using the exact Poisson method. Linked HIV transmission in couples was defined by phylogenetic analysis.

Results: By December 2014, 234 HM-SDC were enrolled: 135 from Australia, 52 from Bangkok and 47 from Rio de Janeiro. There were a total of 150.0 CYFU in 152 couples with at least one follow-up visit of whom 65 (42.8%) were in a non-monogamous relationship. At baseline, 84.2% of HPPs were on cART and in total 82.9% had UVL. STI prevalence was 11.2% in HPPs and 6.6% in HNPs. There were 90.8 CYFU in periods where CLAI was reported with a total of 5,905 acts of CLAI in 88 couples. There were no linked HIV transmissions. The upper limit of the 95% CI of the transmission rate was 4.06/100 CYFU for periods in which CLAI was reported, and 6.46/100 CYFU for periods in which receptive CLAI was reported.

Conclusions: There were no linked HIV transmissions in 150 CYFU in these HM-SDC, despite close to 6,000 acts of CLAI. The upper confidence limit of the transmission rate during follow-up in periods during which CLAI was occurring was 4.06/100 CYFU. These data add to emerging evidence that the rate of HIV transmission in HM-SDC is very low when the HIV-positive partner is on ART. Further follow-up of a larger sample size is required to accurately delineate any residual risk.

  Linked transmissions (n) Couple-years of follow up (CYFU) No. of CLAI acts Incidence rate per 100 CYFU
(95% CI)
Overall 0 149.96 5905 0 (0-2.46)
Any CLAI 0 90.83 5905 0 (0-4.06)
Insertive CLAI 0 77.87 3569 0 (0-4.74)
Receptive CLAI 0 57.08 2337 0 (0-6.46)
Any CLAI when VL <200 copies 0 88.59 5656 0 (0-4.16)
Any CLAI when VL >200 copies 0 2.00 237 0 (0-184)


Session Number: 
Session Title: 
Risk Factors for Transmission in MSM
Presenting Author: 
Grulich, Andrew
Presenter Institution: 
University of New South Wales