Background: Most antibiotics are prescribed in primary care, and most commonly for acute lower respiratory infections (ALRTI). Despite their marginal benefit, about 60% of these infections are currently treated with antibiotics in Catalonia, Spain. Several strategies have been developed to reduce inappropriate antibiotic prescribing, with the use of C-reactive protein (CRP) rapid testing and the improvement of the communication skills being the most effective interventions. However, most studies have been carried out outside Mediterranean countries. This study aims to evaluate the effectiveness and the efficiency of a continuous disease-focused intervention (CRP) and an illness-focused intervention (enhancement of communication skills to optimise doctor-patient consultations and share decision making with the aid of patient-centred leaflets) on antibiotic prescribing in patients with ALRTIs in Catalan primary care centres.

Methods/design: A cluster, randomised, factorial, controlled trial aimed at including 20 primary care centres (n=2,940 patients) with patients older than 18 years presenting for a first consultation with ALRTI, therefore with presence of infected acute cough of up to 3 weeks' duration as the predominant symptom. Centres, according to socioeconomic and antibiotic consumption, will be randomly assigned according to hierarchical clustering to any of four trial arms: usual care, CRP testing, enhanced communication skills backed up with patient leaflets, or combined interventions. A cost-effectiveness and cost-utility analysis will be performed from the perspective of public health system. A qualitative study aimed at identifying the expectations and concerns in patients with ALRTIs and the satisfaction of clinicians with the different interventions will also be performed. Clinicians assigned to the interventions will participate in a 2-hour training workshop before the inception of the trial and will receive a monthly intervention-tailored training module during the trial. Clinical effectiveness will be measured by the antibiotic use within the first 6 weeks and the quality adjusted life years and secondary outcomes will be duration of illness and severity of cough measured with a symptom diary, healthcare reconsultations, hospital admissions and complications. National health care perspective will be adopted and the temporal horizon of the analysis will be one year. Health care costs will be considered and expressed in € of the current year of the analysis. Univariate and multivariate sensitivity analysis will be carried out.

Discussion: The ISAAC-CAT project aims to improve the management of ALRTIs in primary care through use of two different clinicians' skills to help target antibiotic prescribing only to those most likely to benefit, and thereby reduce the risk of unnecessary exposure to antibiotics leading to adverse effects and/or the development of AMR without having a negative impact on health status, thus benefiting individual patients and society at large. This project will contribute to evaluate the effectiveness and efficiency of different strategies for more appropriate antibiotic prescribing that are currently out of the scope of the actual guidelines.