Preventing HIV in Victoria's vulnerable populations: the impact of early and regular testing

Whilst declines in HIV epidemics globally have been seen, men who have sex with men (MSM) continue to have elevated risk of HIV. In Australia HIV diagnoses are now at a twenty-year high and similar to other high-income countries, diagnoses are concentrated among MSM. Several factors are believed to be driving HIV among MSM with transmission risks specific to MSM (e.g., transmission probabilities for specific risk behaviours, sexual role versatility, and sexual networks) further mediated by epidemics of other sexually transmissible infections (STIs) and adoption of non-condom risk reduction. In addition, community-level factors such as increasing HIV prevalence and suboptimal testing, diagnosis and treatment coverage further enhance risk. Reducing undiagnosed HIV remains a key challenge for HIV prevention in Australia. Timely HIV diagnoses provide opportunities to interrupt transmission, specifically via post-diagnosis modification of behaviour and HIV treatment-induced reductions in infectiousness. Australia, in its new National HIV Strategy, has set ambitious HIV elimination targets, with a key objective of reducing undiagnosed HIV among MSM. Australian MSM have historically reported high levels of engagement in HIV testing (approximately 90% reported “ever had a test for HIV”) however, there is some evidence that self-report data over estimates HIV testing frequency, suggesting a need to better understand current patterns of HIV testing and risk behaviour among MSM. The research presented in this thesis aimed to better understand the drivers of HIV transmission in Australia, inform local responses focussed on reducing undiagnosed HIV, and ultimately improve the health of communities most affected by HIV in Australia. The primary data for the research in this thesis were from a sentinel surveillance system in Melbourne, Victoria. The sentinel surveillance system captures testing and outcome data from participating primary care clinics alongside demographic and behavioural data from a brief surveillance questionnaire completed at the time of testing. The innovative sentinel surveillance system is nationally recognised, with high coverage of the key HIV risk population in Australia. The research results show suboptimal testing frequencies among many MSM, particularly among MSM self-reporting high-risk behaviour. Although overall HIV testing had increased significantly (2007-2013) only half of MSM returned for HIV testing annually, a third biannually, and one in ten quarterly. Overall increases in HIV testing may have been influenced by initiatives to promote HIV testing among MSM; however research findings in this thesis show health promotion initiatives were unlikely to have resulted in increases in testing to a level needed among MSM to reduce undiagnosed HIV. The effects of suboptimal testing are amplified by ongoing sexual risk; research in this thesis show limited change in sexual risk among MSM presenting for HIV and other STI testing over approximately 18 months. The prevention benefits of increased testing include behaviour change such as increased condom use and seroadaptive practices based on accurate HIV status to mitigate transmission risk and initiation and maintenance of HIV treatment. Timely access to and maintenance of antiretroviral treatment following HIV diagnosis is imperative to realise the full potential of testing as a prevention intervention. Research results in this thesis suggest the associated costs with HIV treatment may be a potential barrier for some people living with HIV in Victoria. This research highlights that there are substantial gains to be made in increasing testing frequency among MSM. Facilitating frequent HIV testing by ensuring models of HIV testing are convenient for MSM is essential to reduce undiagnosed HIV in Australia. Initiatives to increase testing and treatment need to work synergistically within a combination prevention approach. Although it remains unknown by how much HIV testing needs to increase to reduce new HIV infections in Australia, the research results in this thesis can be used to inform future research examining the relative changes increasing testing frequency may have on transmission. The findings in this thesis also contribute to planning the local HIV response and tailoring of HIV prevention packages.