The difference in self-reported and biological measured HIV prevalence: implications for HIV prevention.

In Australia, HIV prevalence estimates among gay men have been mainly based on self-reported HIV status collected in annual behavioural surveys. We measured biological HIV prevalence among gay men in Melbourne, Australia, using a facility based sampling method. We calculated HIV prevalence and used logistic regression to assess correlates of a positive HIV test. A total of 639 gay men were recruited completed a survey and provided oral fluid for HIV testing from seven venues in 2008. The median age of the participants was 35 years (range 18-75 years). Overall biological HIV prevalence was 9.5% (95% CI 7.5-12.0%) compared with 6.3% (95% CI 4.5-8.4%) for self-reported HIV positive status. We found a significant discrepancy between test detected biological and self-report HIV status in our study, with 19 men (31.1%) unaware of their HIV infection. These results highlight the importance of repeatable biological estimates to inform and evaluate HIV prevention strategies.