Objectives: To determine the prevalence, incidence and risk factors for pharyngeal Chlamydia trachomatis in the community based Health in Men (HIM) cohort of HIV negative homosexual men in Sydney, Australia.
Methods: From January 2003, all HIM participants were offered annual screening for pharyngeal chlamydia using BD ProbeTec nucleic acid amplification testing (NAAT). Detailed sexual behavioural data were collected every 6 months, and risk factors for infection and hazard ratios were calculated using Cox regression.
Results: Among 1427 participants enrolled, the prevalence of pharyngeal chlamydia on initial testing was 1.06% and the incidence rate was 0.58 per 100 person-years. More than 50% of all infections were identified on baseline testing and 68% of men with pharyngeal infection had no evidence of concurrent anogenital chlamydia. There was no association of pharyngeal chlamydia with sore throat. Infection was significantly associated with increasing frequency of receptive penile–oral sex with ejaculation with casual partners (p = 0.009), although approximately half of infections occurred in participants not reporting this risk behaviour. Neither kissing nor oro-anal practices were associated with infection.
Conclusion: The incidence of pharyngeal chlamydia infection in the HIM study was relatively low; however, the relatively high prevalence on baseline testing compared to incidence suggests a long duration of infection. Occasional screening for pharyngeal chlamydia in homosexual men who frequently practise receptive oral sex with ejaculation may be warranted.
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Funding: During the study DJT was supported by National Health and Medical Research Council Public Health Scholarship no. 351044 and is currently supported by the Royal Australasian College of Physicians GSK Scholarship for virological research. The National Centre in HIV Epidemiology and Clinical Research and the National Centre in HIV Social Research are funded by the Australian Government Department of Health and Ageing. The Health in Men Cohort study was funded by the National Institutes of Health, a component of the US Department of Health and Human Services (NIH/NIAID/DAIDS: HVDDT Award N01-AI-05395), the Australian Government Department of Health and Ageing (Canberra) and the New South Wales Health Department (Sydney), and the National Health and Medical Research Council (project grant # 400944).
Competing interests: None.
Ethics approval: Granted by the University of New South Wales.
Contributors: DJT performed the analyses and drafted the manuscript; AEG took overall responsibility for the project and assisted in the analyses and drafting of the manuscript; FJ, JI, GPP, BD, PHC, SK and JMK assisted in formulating the analyses and drafting the manuscript.