Prevalence, incidence and risk factors for pharyngeal gonorrhoea in a community-based HIV-negative cohort of homosexual men in Sydney, Australia

Background Pharyngeal gonorrhoea is common in homosexual men and may be important in maintaining community prevalence of anogenital infections. Methods From 2003, all participants in the Health in Men cohort of HIV-negative homosexual men in were offered annual pharyngeal gonorrhoea screening BD ProbeTec nucleic acid amplification (NAAT) assay with supplementary porA testing. Participants self-reported diagnoses of pharyngeal gonorrhoea made elsewhere between interviews. Detailed sexual behavioural data were collected 6-monthly. Results Among 1427 participants enrolled, 65 study-visit-diagnosed pharyngeal gonorrhoea infections were identified (incidence 1.51 per 100 person-years, 95% 1.19 to 1.93) of which seven infections were on baseline testing (prevalence 0.57%, 95% CI 0.23 1.17%). Almost 85% of study-visit-diagnosed infections occurred without concurrent anogenital gonorrhoea. The combined incidence of study-visit-diagnosed and self-reported pharyngeal gonorrhoea (n = 193) was 4.45 per 100 person-years (95% CI 3.86 5.12). On multivariate analysis, incident infection was associated with younger age (p-trend=0.001), higher number of male partners (p-trend=0.002) and contact with gonorrhoea (p<0.001). Insertive oro-anal sex ('rimming') was the only sexual behaviour independently associated with incident pharyngeal gonorrhoea (p-trend=0.044). Conclusions The majority of pharyngeal gonorrhoea occurred without evidence of concurrent anogenital infection, and the high incidence-to-prevalence ratio suggests frequent spontaneous resolution of NAAT-detected infection. The association of pharyngeal gonorrhoea with oro-anal sex indicates that a broader range of sexual practices are likely to be involved in transmission of gonorrhoea to the pharynx than previously acknowledged. Screening the pharynx of sexually active homosexual men could play a role in reducing the prevalence of anogenital Neisseria gonorrhoeae.