1. Swiss Tropical and Public Health Institute; 4002 Basel Switzerland
2. University of Basel; 4001 Basel Switzerland
3. Institute of Social and Preventive Medicine, University of Bern; 3012 Bern Switzerland
4. Department of Health Sciences and Health Policy; University of Lucerne; 6002 Lucerne Switzerland
5. Pediatric Hematology-Oncology Unit, University Children's Hospital Zurich, University of Zurich; 8032 Zurich Switzerland
6. Pediatric Hematology-Oncology Unit, University Children's Hospital Basel, University of Basel; 4056 Basel Switzerland