Background Concurrency is an important risk behaviour for STI transmission at the population level, yet few surveys ask detailed questions about concurrency. Even if partnerships do not overlap, there is potential for STI transmission if the gap between the end of one partnership and the start of the next is short. We examined the prevalence of concurrency, quantified the gap between partners and examined gender differences in a high-risk population.

Methods Cross-sectional survey of 2203 people attending four contrasting GUM clinics in England in 2009. Attendees completed a questionnaire including questions about their three most recent partnerships in the 3 months prior to attending GUM. Gaps between partners were calculated as the time between most recent sex with a previous partner and first sex with a more recent partner. Partnerships were considered concurrent if the gap was negative.

Results 92% of attendees reported sex partner(s) in the last 3 months, yet, while the median number of partners was 1387 men (48%) and 294 women (28%) reported 2+ partners in this time (p<0.001). For 49% of these attendees, ≥2 of their 3 most recent partners were concurrent (p=0.07 for gender difference). Among the 347 concurrent partnerships reported, the median overlap was long: 113 days (IQR: 28–460 days) with just 40 partnerships (12%) involving an overlap of <2 weeks (no significant gender difference). 40% of attendees with concurrent partners had not used condoms consistently with either partner, and a further 24% of attendees with concurrent partners reported not using condoms at all with either partner. In addition (see Abstract O2-S1.02 figure 1), while 78% of men's partners and 70% of women's were overlapping or had a brief gap (<2 weeks), just 12% and 20% respectively involved a gap between partners of >4 weeks.

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Abstract O2-S1.02 Figure 1

Cumulative percentage distribution of the time between partners in the 3 months prior to attending GUM clinic reported by attendees with 2+ partners, by gender.

Conclusions The majority of GUM attendees reported few partners in the last 3 months, yet half of those with 2+ partners had concurrent partnerships, such that concurrency is as common as serial monogamy in this population. These partnerships typically overlapped by a number of weeks and condoms were seldom used, if at all. Among the serially monogamous, sex with a new partner within days of last sex with a former partner was common so the potential for STI transmission is high. Understanding concurrency and the gaps experienced by high-risk individuals is important for ensuring that health promotion and partner notification are delivered appropriately and effectively.