Abstract

Microbiological reference materials are being developed by the RIVM since several years. These materials consist of capsules filled with milkpowder artificially contaminated with a bacteria test strain of choice (i.e. Escherichia coli, Enterobacter cloacae, Salmonella typhimurium). Both from longterm stability tests, and from short-term challenge tests at different storage temperatures, it is clear that these materials cannot survive forever. Standard statistical techniques for quality control, assuming both a stable process and the Normal distribution cannot be used. In this report we will deal with these non-standard problems.