Background To facilitate opportunistic chlamydia screening in general practices, a complex intervention (3Cs and HIV), based on the previously successful CIRT trial, was implemented across England. The intervention, to encourage practice staff to routinely offer chlamydia testing, only increased chlamydia screening in larger practices or in those offered incentives.

Aims a) Explore why the modified intervention did not increase screening across all general practices. b) Suggest recommendations for future intervention implementation.

Methods Phone interviews were carried out with 26 GP staff exploring their opinions on the workshops and intervention implementation in practice. Interview transcripts were thematically analysed and further examined using the fidelity of implementation model.

Results Participants were positive about the workshops but attendee numbers were low. Often, the intervention content was not adhered to: practice staff were unaware of any on-going trainer support; computer prompts were only added to the female contraception template; patients were not encouraged to complete the test immediately; and videos and posters were not utilised, as suggested. Staff reported that financial incentives, themselves, were not a motivator; competing priorities and time were identified as major barriers.

Conclusions Not adhering to the exact intervention model may explain the lack of significant increases in chlamydia screening. To increase fidelity of implementation and consequently improve likelihood of increased screening, the intervention needs to have: more specific action planning; computer prompts added to systems and used; all staff attend the workshop; and on-going practice staff support.