Current research gaps: a global systematic review of HIV and sexually transmissible infections among transgender populations.

Transgender populations are heavily burdened by HIV and other sexually transmissible infections (STIs). However, data on co-infection with HIV and STIs among transgender people are limited. A systematic review was conducted of peer-reviewed articles and conference abstracts between January 2010 and November 2015 that focussed on HIV and STI infections among transgender populations globally. The literature was synthesised and opportunities for improving health research were commented on. Few studies reported HIV-STI co-infection (n=4), while the majority of studies reported HIV and STI infections separately (n=23). Most studies were conducted outside of the USA (n=19), and all but one of these studies reported data on transgender women only. Among USA-based studies (n=8), several reported data on both transgender men and transgender women (n=3), whereas other studies reported exclusively on transgender men (n=1) or transgender women (n=4). Understanding HIV and STIs among transgender people requires research that simultaneously considers multilevel drivers of vulnerabilities. More data are needed on how the interaction of individual determinants, including biological risks of transmission, programmatic determinants such as service-delivery models and policy-level determinants including institutionalised stigma in healthcare settings, influence the HIV- and STI-related outcomes of transgender populations. Leveraging the knowledge of transgender-specific determinants of HIV and STIs should guide the content and approaches to future HIV and STI prevention and treatment efforts.