Incidence of repeat testing and diagnoses of Chlamydia trachomatis and Neisseria gonorrhoea in swingers, homosexual and heterosexual men and women at two large Dutch STI clinics, 2006-2013

Objective Swingers, that is, heterosexuals who as a couple have sex with others, including group sex and bisexual behaviour, are an older-aged risk group for STIs. Here, we report on their repeat testing (reattendance) and STI yield compared with other heterosexuals and men who have sex with men (MSM, homosexual men) at two Dutch STI clinics.Methods Swingers are routinely (since 2006, South Limburg, registration-completeness: 99%) or partially (since 2010, Amsterdam, registration-completeness: 20%) included in the clinic patient registries. Data (retrospective cohort) are analysed to assess incidence (per 100 person-years (PY)) of reattendance and STI (Chlamydia trachomatis (CT) and/or Neisseria gonorrhoeae (NG)) and associated factors calculating HRs.Results In South Limburg 7714 and in Amsterdam 2070 swinger consultations were identified. Since 2010, swingers' incidence of reattendance was 48-57/100 PY. Incidence was lower in MSM (30-39/100 PY, HR 0.56; 95% CI 0.51 to 0.61, South Limburg; HR 0.88; 95% CI 0.80 to 0.96, Amsterdam), heterosexual men (8-14/100 PY, HR 0.16; 95% CI 0.15 to 0.17, South Limburg; HR 0.33; 95% CI 0.30 to 0.36, Amsterdam) and women (13-20/100 PY, HR 0.56; 95% CI 0.51 to 0.61, South Limburg; HR 0.46; 95% CI 0.42 to 0.51, Amsterdam). Swingers' STI incidence at reattendance was 11-12/100 PY. Incidence was similar in heterosexual men (14-15/100 PY; HR 1.19; 95% CI 0.90 to 1.57, South Limburg; HR 1.20; 95% CI 0.91 to 1.59, Amsterdam) and women (12-14/100 PY; HR 1.14; 95% CI 0.88 to 1.49, South Limburg; HR 0.98; 95% CI 0.74 to 1.29, Amsterdam) and higher in MSM (18-22/100 PY; HR 1.59; 95% CI 1.19 to 2.12, South Limburg; HR 1.80; 95% CI 1.36 to 2.37, Amsterdam). Risk factors for STI incidence were partner-notified (contact-tracing), symptoms and previous STI. Swingers' positivity at any clinic attendance was 3-4% for NG (ie, higher than other heterosexuals) and 6-8% for CT (ie, lower than heterosexuals overall but higher than older heterosexuals).Conclusions Systematic identification reveals that swingers are part of the normal STI clinic populations. They frequently repeat test yet are likely underrecognised in clinics which not routinely ask about swinging. Given swingers' notable STI rates, usage of services is warranted, although use may be restricted, that is, to those with an STI risk factor (as did Dutch clinics). As swingers have dense sexual networks, enhancing contact-tracing may have high impact.