1. Department of Surgery, Orbis Medical Center, Sittard-Geleen, The Netherlands.
2. Department of Medical Microbiology and Infection Control, Orbis Medical Center, Sittard-Geleen, The Netherlands.
3. Department of Methodology and Statistics, Maastricht University, Maastricht, The Netherlands.
4. Department of Surgery, Maastricht University Medical Center, Maastricht, The Netherlands.