“This complex intervention within the English chlamydia screening programme led to a 76% increase in chlamydia screening test rates across all practices offered the intervention, with a 40% increase in infections detected.”1 Thus begins the Discussion section of the article by McNulty, et al in this edition of Sexually Transmitted Infections. On the surface, the finding appears dramatic, offering hope for a major advance in the coverage of screening for chlamydial infection under the UK's National Chlamydia Screening Programme. Look a little deeper, however, and chlamydia screening clearly remains a major challenge.

McNulty et al1 conducted a cluster randomised controlled trial using a ‘Modified Zelen’ design to assess the impact of an intervention developed to alter the screening behaviours of general practices in the southwest of England. Over 150 practices were randomised: 77 to receive the intervention and 83 to serve as control practices. The intervention, developed using the Theory of Planned Behaviour,2 incorporated an outreach educational workshop, posters, invitation cards, feedback on practice performance and ongoing support to the practices. Grounding the intervention in the Theory of Planned Behaviour provided a strong framework and justification for each component of the intervention and is a fundamental strength of this study.

The uptake of the intervention was modest: only 62% of intervention practices agreed to three contacts with a chlamydia support worker and 17% refused all contacts. Additionally, only 45% of practices used computer prompts and about two-thirds used invitation cards. Use of posters was more common, with about 80% of practices using posters.

Given the modest …