Background During outreach activities of our public health STI-clinic a group of young men was encountered, who engaged in internet escort activities. Their commercial sex activities with men took place hidden from public sight and regular health care. This study aims to describe the STI incidence and risk behaviour in these male sex workers having sex with men (MSW), compared to female sex workers (FSW) and men who have sex with men (MSM) attending the same STI-clinic.

Methods Retrospective cross-sectional study among self-identified MSW, FSW and MSM at our STI-clinic in the Netherlands (January 2009-May 2012). All clients completed a questionnaire on sexual behaviour and were tested for STI: at multiple anatomic sites (anal, genital, oral) for chlamydia and gonorrhoea, and in serum for hiv, hepatitis B and syphilis. Clinical consultations (n = 3716) from MSW (n = 203), FSW (n = 801) and MSM (n = 2712) were compared using chi-square statistics.

Results A new STI was diagnosed in 42% of MSW; this proportion was lower in MSM (14%; p < 0.01) and FSW (9%; p < 0.01). Of MSW 8% showed a new hiv-infection (0% in FSW; p < 0.01 and 1% in MSM; p = 0.03).

Majority (87%) of MSW originated from Eastern Europe, their median age was 24 years. Less than half of the men self-identified as homosexual, and indeed 58% also reported sex with women (28% of MSM; p < 0.01). MSW reported sex contacts with (other) sex workers (18%) more often than FSW (0%, p < 0.01) and MSM (3%, p < 0.01).

Conclusion MSW are at a high risk for contracting and transmitting STI from and to their clients, but also from and to non-commercial (female) contacts and within their own MSW network. This makes them a potential bridging population for STI transmission. While the MSW population is largely hidden, we prove that it is feasible to reach them with care.