Incidence and risk factors for urethral and anal gonorrhoea and chlamydia in a cohort of HIV negative homosexual men: the HIM study

¹ National Centre in HIV Epidemiology and Clinical Research, UNSW, Australia
² National Centre in HIV Social Research, UNSW, Australia
³ Taylor Square Private Clinic, Darlinghurst, Australia
⁴ Sydney Sexual Health Centre, Sydney Hospital and NCHECR, UNSW, Australia
⁵ Centre for Immunology, St Vincent's Hospital, Sydney, Australia

^* To whom correspondence should be addressed. E-mail: jjin{at}nchecr.unsw.edu.au.

Accepted 26 September 2006

	Abstract

Background: Early detection and treatment of bacterial sexually transmitted infections has been advocated as an HIV prevention strategy. In order to inform screening guidelines, we determined incidence and risk factors for urethral and anal gonorrhoea and chlamydia in a prospective cohort of community-based HIV negative homosexual men in Sydney.

Methods: We offered all participants annual screening for gonorrhoea and chlamydia ("study visit diagnoses") on urine and anal swabs using nucleic acid amplification (BD ProbeTec). They also reported diagnoses of gonorrhoea and chlamydia made elsewhere between interviews ("interval diagnoses"). We summed all diagnoses to create a combined incidence rate, and collected detailed data on specific sexual practices with casual and regular partners.

Results: Among 1,427 men enrolled, the combined incidence rates were 3.49 and 2.96 per 100 person-years (PY) for urethral and anal gonorrhoea, respectively; and 7.43 and 4.98 per 100 PY for urethral and anal chlamydia, respectively. Urethral infections were associated with unprotected anal intercourse (UAI) with HIV positive partners (HR=2.58, 95% CI 1.10-6.05 for urethral gonorrhoea), and with frequent insertive oral sex (p trend=0.007 for urethral chlamydia). Anal infections were associated with receptive UAI (p trend=0.001 for both anal gonorrhoea and chlamydia) and other receptive anal sexual practices. Stratified analyses further demonstrated the independence of the associations of insertive oral sex with urethral infections and non-intercourse receptive anal practices with anal infections.

Conclusion: Incident gonorrhoea and chlamydia were common. Risk behaviours for both urethral and anal infections were not restricted to UAI. Screening which includes tests for anal and urethral infections should be considered for all sexually active homosexual men, not just those who report UAI.

Key Words: Australia, Chlamydia, Cohort study, Gonorrhoea, Homosexuality, male

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