The reprocessing of medical devices is an essential process to keep a hospital functional. It is carried out in the Central Sterilization Supply Department (CSSD). Failures during reprocessing can endanger patients' safety and increase costs. The benefits of an assistance system helping workers in preventing failures are therefore obvious, whereas challenging requirements arise through process complexity, legislation, integration and hygiene restrictions. We propose an assistance system that supports the worker in the unclean area of a CSSD under these requirements. It provides a user interface for context-aware guidance and collection of process relevant data from the worker. 'Virtual touches' fulfill the hygiene requirements and are realized with a depth camera and a projected user interface. Business process models control the workflow and maintain a valid database for quality assurance and worker guidance. We evaluated the system with a user study focusing on failure prevention, task completion time and usability. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstracting with credit