Background This study presents an intervention and its evaluation of an innovative approach to counteract barriers to safe sex and STI testing of youth aged 16–24.

Methods The intervention—http://www.vrijlekker.nl/—has been developed based on over 200 qualitative interviews with youth investigating barriers to safe sex and STI testing. Based on these interviews, training modules were developed which participants could follow online. These modules aimed at counteracting the individual barriers for safe sex and STI testing as well as removing impeding elements in the social and sexual network. The Information-, Motivation and Behavioural Skills (IMB) model (Fisher & Fisher) was used as the theoretical basis of the intervention. The training included filmed coaches that guided users throughout the intervention, thematic films, interactive text with personal feedback and sexual network tools. The modules were offered on a tailored basis to match each user's own cognitive & behavioural risk profile. This profile was established via an automated online intake. An evaluation was conducted comparing a demographically matched control group recruited prior to the launch of the intervention and an intervention group. Behavioural outcomes were compared at 6 month follow-up.

Results The evaluation included 2944 participants of whom 1553 completed the follow-up (mean age 19, SD 2.4). The intervention group used condoms significantly more often with their most recent casual partner [OR=1.82 95% CI 1.08% to 3.04%] and/or with their steady partner [OR=2.17 95% CI 1.48% to 3.18%] than the control group at 6 months follow-up. Over 170 000 unique persons used the intervention already during its first year, and more than 100 new users continue to do so every day. Some schools in the Netherlands have adopted the site as part of their routine sexual education program.

Conclusions This study has shown than offering youth an empirically and theoretically sound intervention that is interactive and which adapts itself to the individual needs of each user and its sexual network, results in a desired behavioural change and high uptake, even among the challenging target group of youth.