Diagnoses of sexually transmissible infections in HIV-serodiscordant male couples in Australia, Brazil and Thailand

Background In an era of biomedical prevention of HIV transmission, prevention of sexually transmissible infections (STIs) remains a priority for male HIV-serodiscordant couples. Three common STIs in populations of gay and bisexual men are chlamydia, gonorrhoea and syphilis. Methods We examined the incidence of these three infections in 343 male HIV-serodiscordant couples in Australia, Brazil and Thailand. The couples participated in a prospective, observational cohort study that included regular STI testing and behavioural surveys for HIV-negative partners (HNP). Results HIV-positive partners (HPP; IR=22.9/100person-years, 95% CI: 19.3-27.0) had a higher incidence rate of any STI (22.9/100person-years, 95% CI: 19.3-27.0) compared with HNP (14.9/100person-years, 95% CI: 12.1-18.3). It was more common for only the HPP (n =107/343, 7.1%) or only the HNP (n =60, 4.0%) to have an STI than for both to have an STI (n =29/343, 1.9%). Higher STI incidence was associated with vocational education (HNP: aHR=2.19, P =0.005), full-time employment (HPP: aHR=1.61, P =0.016), living in Brazil (HPP: aHR=1.85, P =0.017) or Thailand (HPP: aHR=1.98, P =0.008), having anal sex with other partners (HNP: aHR=2.42, P =0.003; HPP: aHR=2.87, P P =0.044). Lower STI incidence was associated with age >40 years (HNP: aHR=0.49, P =0.021; HPP: aHR=0.46, P =0.006), full-time employment (HNP: aHR=0.56, P =0.016) and >5years since first sex with the study partner (HNP: aHR=0.50, P =0.036). Conclusions There were differences in STI diagnoses within HIV-serodiscordant couples, particularly based on their agreements about sex outside the relationship. Interventions aimed at strengthening these agreements with commitments to STI testing could be effective in reducing the incidence of STIs.