This thesis presents data on two separate areas relevant to the prevention of HIV and sexually transmitted infection (STI) transmission in homosexual men. These data arise from the community-based Health in Men (HIM) cohort of HIV-negative homosexual men in Sydney. First, the association of circumcision status with HIV and STIs was examined. Older age, ethnicity and country of birth were demographic factors independently associated with circumcision status. Self-report was a valid measure of circumcision status in this population. Overall, being circumcised was associated with a non-significant reduced risk of HIV seroconversion in the HIM cohort (HR 0.76, 95% CI 0.41-1.41, p=0.381). Among the one-third of participants predominantly practising the insertive role in anal intercourse (AI), being circumcised was associated with a significantly reduced risk of HIV infection (HR 0.15, 95% CI 0.03-0.80, p=0.026). Circumcised HIM participants also had a lower risk of incident syphilis (HR 0.35, 95% CI 0.15-0.84, p=0.019), however circumcision status had no significant effect on the remainder of prevalent and incident STIs examined. Second, risk factors for pharyngeal gonorrhoea and chlamydia were investigated. The BD ProbeTec nucleic acid amplification test (NAAT) had a positive predictive value (PPV) for pharyngeal gonorrhoea diagnosis of only 30.4% (95% CI 25.2-36.1%) when compared to a previously validated NAAT targeting the gonococcal porA pseudogene. Pharyngeal gonorrhoea was common in HIM, mostly occurred without concurrent anogenital infection and may frequently spontaneously resolve. Infection was independently associated with younger age (p-trend=0.001), higher number of male partners (p-trend=0.002), contact with gonorrhoea (p<0.001) and insertive oro-anal sex with casual partners (p-trend=0.044). Pharyngeal chlamydia was less common but a high prevalence/incidence ratio suggested that infection may persist in the pharynx for long periods. Pharyngeal chlamydia was independently associated with receptive penile-oral sex with casual partners (p-trend=0.009). In conclusion, circumcision may have a role as an HIV prevention intervention among the subgroup of homosexual men who predominantly practise insertive rather than receptive AI. Regular screening of the pharynx including a validated supplemental NAAT for gonorrhoea diagnosis may prevent much transmission to anogenital sites, whereas chlamydia occurs too infrequently in the pharynx to recommend routine screening in homosexual men.

This thesis presents data on two separate areas relevant to the prevention of HIV and sexually transmitted infection (STI) transmission in homosexual men. These data arise from the community-based Health in Men (HIM) cohort of HIV-negative homosexual men in Sydney. First, the association of circumcision status with HIV and STIs was examined. Older age, ethnicity and country of birth were demographic factors independently associated with circumcision status. Self-report was a valid measure of circumcision status in this population. Overall, being circumcised was associated with a non-significant reduced risk of HIV seroconversion in the HIM cohort (HR 0.76, 95% CI 0.41-1.41, p=0.381). Among the one-third of participants predominantly practising the insertive role in anal intercourse (AI), being circumcised was associated with a significantly reduced risk of HIV infection (HR 0.15, 95% CI 0.03-0.80, p=0.026). Circumcised HIM participants also had a lower risk of incident syphilis (HR 0.35, 95% CI 0.15-0.84, p=0.019), however circumcision status had no significant effect on the remainder of prevalent and incident STIs examined. Second, risk factors for pharyngeal gonorrhoea and chlamydia were investigated. The BD ProbeTec nucleic acid amplification test (NAAT) had a positive predictive value (PPV) for pharyngeal gonorrhoea diagnosis of only 30.4% (95% CI 25.2-36.1%) when compared to a previously validated NAAT targeting the gonococcal porA pseudogene. Pharyngeal gonorrhoea was common in HIM, mostly occurred without concurrent anogenital infection and may frequently spontaneously resolve. Infection was independently associated with younger age (p-trend=0.001), higher number of male partners (p-trend=0.002), contact with gonorrhoea (p<0.001) and insertive oro-anal sex with casual partners (p-trend=0.044). Pharyngeal chlamydia was less common but a high prevalence/incidence ratio suggested that infection may persist in the pharynx for long periods. Pharyngeal chlamydia was independently associated with receptive penile-oral sex with casual partners (p-trend=0.009). In conclusion, circumcision may have a role as an HIV prevention intervention among the subgroup of homosexual men who predominantly practise insertive rather than receptive AI. Regular screening of the pharynx including a validated supplemental NAAT for gonorrhoea diagnosis may prevent much transmission to anogenital sites, whereas chlamydia occurs too infrequently in the pharynx to recommend routine screening in homosexual men.