1. Department of General Practice, The Antibiotic Centre for Primary Care, Institute of Health and Society, University of Oslo , Oslo , Norway
2. Department of General Practice, Institute of Health and Society, University of Oslo , Oslo , Norway
3. Department of General Practice, General Practice Research Unit (AFE), Institute of Health and Society, University of Oslo , Oslo , Norway
4. Vårdcentralen Värmlands Nysäter and Centre for Clinical Research, County Council of Värmland, Varmlands Nysater , 661 95 Karlstad , Sweden
5. Department of Medical Epidemiology and Biostatistics, Karolinska Institutet , Stockholm , Sweden
6. School of Medical Science, University of Örebro , Örebro , Sweden