1. Institute of General Practice, Charite University Hospital Berlin, 10117 Berlin, Germany
2. Department of General Practice, University Hospital Wuerzburg, 97080 Wuerzburg, Germany
3. Institute of General Practice, University Hospital Jena, 07743 Jena, Germany
4. Robert Koch Institute, 13353 Berlin, Germany
5. Institute of General Practice/Primary Care, Faculty of Medicine and Medical Center, University of Freiburg, 79110 Freiburg im Breisgau, Germany
6. Department of Health Service Research, Institute for Public Health and Nursing Research, University of Bremen, 28359 Bremen, Germany