Incidence and transmission risks for HIV, syphilis and chlamydia in men who have sex with men: findings from a primary care sentinel surveillance network in Victoria, Australia
M. Stoove1, C. El-Hayek1, J. Goller1, R. Guy2, A. Wilkinson1, J. Gold1, I. Bergeri1, M. Gouillou1, T. Spellman1, M. Hellard1
1Burnet Institute, Centre for Population Health, Melbourne, Australia, 2University of Sydney, National Centre for HIV Epidemiology and Clinical Research, Sydney, Australia
Background: Alongside many Western countries, HIV diagnoses in MSM in Australia have increased over the past decade, most markedly in Victoria, the second most populous state. Diagnoses of syphilis and chlamydia have also increased.
Methods: To determine incidence and the transmission risks associated with HIV, chlamydia and syphilis among MSM, we conducted retrospective cohort analyses of MSM tested for these three infections from April 2006 to December 2008 at four metropolitan clinics participating in the Victorian Primary Care Network for Sentinel Surveillance (VPCNSS). The person-years (PY) method among repeat testers was used to determine incidence and Cox regression used to identify correlates of incidence.
Results: Over 33 months there were 13,615 HIV, 21,757 syphilis, and 18,061 chlamydia tests conducted among MSM. HIV incidence was 1.3 per 100 PY (95% confidence interval [CI] 1.0-1.8). Reporting >5 sex partners in the last six months, a current HIV positive regular partner, and inconsistent condom use with regular partners were significant multivariate correlates of HIV incidence. Syphilis incidence was 2.9 per 100 PY (95%CI 2.6-3.4); 4.3 per 100 PY in HIV positive MSM (95%CI 3.5-5.1), compared to 2.1 per 100 PY (95%CI 1.7-2.6) in HIV negative MSM. Chlamydia incidence was 10.6 per 100 PY (95%CI 9.7-11.6). Being aged < 29 years, HIV positive status, reporting sex work, and presenting with symptoms were significant multivariate correlates of chlamydia incidence.
Conclusions: By combining behavioural and testing data in clinic populations, the VPCNSS provides timely information about HIV/STI incidence and transmission risk in MSM, helping to inform prevention activities in Australia. Over time, linking individuals’ behavioural and testing data across multiple STIs in the VCPNSS will provide estimates of the contribution of both risk behaviours and concurrent infections to STI transmission among MSM.