Agreements, Behaviour, and Change: Sex Outside the Relationship in Male HIV-negative Partners in HIV Serodiscordant Relationships in Australia, Brazil, and Thailand.

Male HIV serodiscordant couples have diverse relationship agreements regarding sex outside the relationship. We examined the relationship agreements as described by 343 male HIV-negative partners in HIV serodiscordant relationships in Australia, Brazil and Thailand participating in a multi-year cohort study. At baseline, 125 (34.1%) HIV-negative partners reported no agreement, 115 (33.5%) had a monogamous agreement, and 103 (37.9%) had an open agreement allowing sex outside the relationship. Relationship agreements were largely stable over time, with 76% of HIV-negative men reporting the same agreement across follow up, while changes were predominantly towards having an open agreement. Behaviour largely matched relationship agreements, and the predictors of breaking an agreement by having condomless anal intercourse (CLAI) with an outside partner were CLAI within the relationship (OR = 3.17, 95%CI: 1.64-6.14, p < 0.001) and PrEP use in the last three months (OR = 3.42, 95%CI: 1.48-7.92, p = 0.004). When considering HIV transmission risk for HIV-negative men in serodiscordant relationships, greater focus needs to be placed on sex that is occurring outside the relationship and the agreements that facilitate this.