The research question will be answered using aggregated data in an ecological study design. We define the appropriateness of prescribing as the congruency between resistance patterns and prescription patterns; this will be operationalised as the odds that a patient will be given an effective drug. Data collection will be done within the APRES study (The appropriateness of prescribing antibiotics in primary care in Europe with respect to antibiotic resistance). The study will be conducted in nine countries in Europe: Austria, Belgium, Croatia, France, Hungary, the Netherlands, Spain, Sweden and the United Kingdom. We chose to include countries with different levels of prescription behaviour, to maximize our analysis range.
GP practices (20 per country) are recruited through an existing GP network in each country . This network should be representative of the GPs in that country or region as much as possible, and a prerequisite is the ability to deliver electronic prescription data of the participating practices for the past five years. Geographical spread will be obtained by recruiting practices in both rural as well as urban areas. Some countries (Spain, Croatia) will also include primary care paediatricians as these are the ones that deliver primary care to children in these countries.
The study will be carried out in the primary care setting and the target population is the community based without bacterial infections as a proxy for the general population. We use an opportunistic random sample of visitors of general practices. In the waiting room information leaflets and posters are used for recruitment purposes. All countries use the same inclusion criteria:
No antibiotic use in the past 3 months
No hospitalisation in the past 3 months
Registered patient or regular visitor of the practice for at least 1 year
Age 4 years and older (UK: 18 and over)
No residents of nursing homes
No existing infectious disease at time of visit for which antibiotics are prescribed
No terminal illness
No out of hour consultations
During the period of data collection (November 2010 - May 2011) each practice recruits 200 patients to participate in the study. A Dutch study with the same design proved this to be feasible . The data collection is spread across several months to maximize the potential detection of S. pneumoniae .
Whether a patient meets the inclusion criteria will be assessed by the GP or qualified practice nurse. Most criteria are apparent at first sight; others are asked when the patient is invited to participate. Regarding age and gender we strive for an equal stratification along the different groups; male, female and children (4-19), middle age (20-65) and elderly (> 65 years old). Recruitment will be monitored with a two-weekly update about the recruitment.
A nasal swab is taken from all participants by the GP or qualified practice nurse. The swabs are sent to one laboratory in each country using special envelopes. They should arrive within 48 hours, to increase the survival rate of S. pneumoniae. As a consequence of the ethical approval procedure, in the UK the nasal swabs are taken by the patients themselves, at home. All patients from whom a nasal swab was taken fill in a short questionnaire regarding their background and confounding variables. The national laboratories will isolate the bacteria (Staphylococcus aureus and Streptococcus pneumoniae) from the swabs (for the isolation procedures see additional file 1: Appendix A). These bacteria were selected because of their high impact on health care . Prior to the swabbing period, the national laboratories are evaluated regarding the quality of their isolation procedures.
At the end of the data collection period, the isolated bacteria will be sent to the Department of Medical Microbiology of Maastricht University, the central laboratory of the project where the resistance testing will be performed. The antibiotic susceptibility of the isolated strains will be determined quantitatively using a broth dilution method in micro-titre plates according to the EUCAST standard . The compounds tested include penicillins with and without beta-lactamase inhibitors, cephalosporines, macrolides, tetracyclines, quinolones, trimethoprim-sulfamethoxazole and rifampicin. For S. aureus also aminoglycosides and topical agents (fusidic acid and mupirocin) will be tested. This analysis will result in a resistance rate for every bacterium - antibiotic combination.
Sample size calculation
In a recent study among 2,000 community-dwelling persons in the Netherlands, 23% showed to be carrier of Staphylococcus aureus, whereas 4% showed to be resistant against antibiotics . Power analysis showed that using a one-sided t-test (alpha = 0.05) testing for a 50 percent difference (4% versus 6%) between countries with a power of 0.95, 1,000 isolates are needed. For 1,000 isolates, 4,000 swabs have to be taken in each country. Therefore, for nine countries the total data collection will consist of 36,000 swabs.
The GPs and GP practices who are participating in swabbing the patients also take part in the collection of prescription data.
We will collect data about all prescribed antibiotics from the participating practices for the past 5 years (i.e. calendar years 2006 to 2011). For every prescription of antibiotics, i.e. antibacterials for systemic use according to the Anatomical Therapeutic Chemical (ATC) classification (ATC code J01), we will collect the following information:
Date of the prescription;
Diagnosis for which the antibiotic has been prescribed (if available);
Identification of the chemical substance (7 digit ATC code);
Number of packages (if available);
Number of Defined Daily Dose (DDD's, if available).
The diagnostic data will be converted to the International Classification of Diseases,10th revision (ICD-10) . No additional data collection is needed; all these data are routinely recorded in the patients' electronic medical records.
Data on characteristics of the practice population (the epidemiological denominator) including the size of the practice population and its age (in 5-year age bands) and sex distribution will also be collected. In countries with a registered list system, this file can be retrieved from the practice computer. In countries without a registered list system, estimates of the size and composition of the population will be provided  either based on characteristics of the patients visiting the practice, or based on extrapolation of local or regional population characteristics .
Finally, each practice will provide information on a few practice characteristics in a short questionnaire (geographical area, number of listed patients, number of physicians working in the practice, age of the physicians).
In addition to the aforementioned data collection, relevant antibiotic treatment guidelines used in the nine participating countries will be collected and evaluated in relation to the resistance patterns in each country. In particular, we will focus on syndromes and diseases mainly caused by S. aureus and S. pneumoniae: skin infections and pneumonia respectively. In cooperation with the GP networks in the countries, we will assess the most frequently used primary care guidelines on both content (specific recommendations) and quality. For the latter we will use a standardised instrument, with a focus on the evidence base of the recommendations [30–33].
By comparing the current resistance patterns with the primary care guidelines per country, we will be able to make recommendations to improve these guidelines, incorporating the evidence we will collect.
In every participating country ethical approval for this study has been obtained. All participants sign an informed consent form. For children a separate form is developed, where consent from one of their parents or their guardian is obtained. Children are not allowed to participate in the UK due to ethical restrictions.