1. West-German Centre of Diabetes and Health, Düsseldorf Catholic Hospital Group, Düsseldorf, Germany
2. Occupational Health Services, Kassenärztliche Vereinigung Nordrhein, Düsseldorf, Germany
3. Occupational Health Services Ärztekammer Nordrhein, Düsseldorf, Germany
4. Occupational Health Services Eickhoff GmbH, Bochum, Germany