Aseptic packaging machine pre-sterilisation and package sterilisation: statistical aspects of microbiological validation

Validation of the pre-sterilisation of an aseptic packaging machine and validation of the machine's sterilisation of the packages require many evaluations, including a microbiological challenge. This paper describes the statistical considerations supporting the microbiological challenge, focusing especially upon the use of the most probable number (MPN) technique. The uniformity of the log count reduction (LCR) must be demonstrated for the standard sterilisation technique to be applied to the machine and to the packages. The sites in the machine expected to receive the least sterilisation effect must be identified, and all sites in the machine must be verified independently of each other. If the uniformity of sterilisation can be shown for the packages, these can be evaluated as large sets of replicates, achieving considerable precision of the LCR. The MPN technique requires evaluation of the improbability of the results and must use credible estimates of the confidence interval. These techniques are thoroughly discussed, and a spreadsheet routine is demonstrated that incorporates the techniques. (C) 1999 Elsevier Science Ltd. All rights reserved.