Background Currently, risk groups are tested only urogenitally by most healthcare providers like general practitioners and STI clinics. Only on indicationmostly guided by symptomsanorectal and/or oropharyngeal tests are performed. Patient identification and thereby adequate treatment and interruption of the chain of transmission can be hampered when patients are positive at another anatomic site than sampled for testing. It is unknown how large this potentially missed STI burden in healthcare is. In this study we assessed the burden of undetected STI in high risk heterosexuals (swingers) and men who have sex with men (MSM), based on systematic testing at three anatomical sites.

Methods All MSM and high risk heterosexuals that is, swingers, who as a couple have sex with other couples, were systematically screened for urogenital, anorectal and oropharyngeal STI at our STI Centre in 2010. This comprised 762 swinger consultations and 597 (non swinging) MSM consultations. One third of the male swingers reported to have sex with men. Prevalences of Chlamydia trachomatis (CT) and Neisseria gonorrhoea (NG), and STI (CT and/or NG) were calculated on multiple anatomical sites as well as the proportion of anorectal and oropharyngeal diagnosis that would have been missed if screened urogenital only.

Results Prevalences were 7% and 10% for CT, and 3% and 5% for NG in swingers and MSM, respectively (Abstract O1-S07.04 table 1). Of all anorectal CT in MSM 86% (n=42) was diagnosed without an urogenital CT, for NG this was 65% (n=11). Seventy-five per cent (n=6) of all oropharyngeal CT and 69% (n=11) of all oropharyngeal NG diagnoses would have been missed if MSM had been tested urogenital only. Prevalence of anorectal CT was higher than that of urogenital CT in female swingers. The proportions of missed anorectal diagnosis for CT were 50% (n=4) and 24% (n=5) for male and female swingers, respectively. No anorectal CT diagnosis was missed in male swingers, but in female swingers this was 67% (n=2). All oropharyngeal CT (n=6) and nearly all NG (91.7%, n=11) infections in swingers were diagnosed without a urogenital infection.

Conclusion MSM and female swingers have high prevalences of anorectal CT which are often diagnosed without a urogenital infection. Therefore these risk groups need a targeted screening strategies including anorectal testing. The prevalence of oropharyngeal STI is relatively low, but it is often an isolated infection and therefore missed by the current screening strategy.