Background Motivational interviewing (MI) can be effective for behaviour change even when tailored to brief encounters. MI is focused on resolving the ambivalence that might prevent change. We have developed and evaluated simple tools to facilitate MI based counselling for reducing high risk sexual behaviour.

Method Patients attending a drop-in STI services reception were offered 20–30 min of MI-based risk-reducing counselling. Out of 110 eligible patients (56 men and 54 women) who had had at least 4 sexual partners during the previous year, 72 patients aged 17–34 years (mean 24.8) participated. A structured manual was developed containing 14 questions, the first 5 of which were aimed at developing and amplifying the patient's motivation to reduce risky behaviour. We discussed with the patients their own perception of STI risks and the importance of not becoming infected, not infecting sexual partners and avoiding pregnancy. At the end of the session, patients were asked to assess their future commitment to changing risky sexual behaviour and a plan for accomplishing this change was drawn up. To ensure treatment fidelity, MI skill was assessed using the Motivational Interviewing Treatment Integrity Coding System (MITI 3.0).

Results At baseline, 4 of 32 men (12.5 %) and 6 of 40 women (15 %) had a genital CT infection. After intervention, the incidence of CT was 6 % in men and 0 % in women in the following12 months. Of those CT-infected at start, none was re-infected within the next year. At baseline, men reported on average 8 (4-35) partners in the previous12 months and women 6 (4–17). On a scale from 0 to 10 men rated their STI-risk in the previous year as 5.5 (1–10) and women as 6.3 (2–10). The corresponding rating for pregnancy risk was 2.7 (0–8.5) for men and 3.3 (0–9) for women. Men rated the importance of not becoming infected as 8.5 (5–10) and women as 9.5 (5–10). The importance of not infecting a sexual partner was rated as 9.2 (2.5–10) in men and 9.6 (6–10) in women. The importance of avoiding pregnancy was rated as 9.2 (5–10) in men and 9.5 (2–10) in women. The ability to reduce sexual risks was judged as 8.4 (5–10) in men and 8.6 (3.5–10) in women. At the end of the session, patients' commitment to reducing STI risks was 9.1 (6–10) for men and 9.3 (8–10) for women.

Conclusion Brief MI-based single-session counselling aimed at assessing personal risks, resolving ambivalence, developing risk-reduction strategies and implementing safer sex behaviours is effective in the reduction of high-risk sexual practices and CT incidence.