Abt. Allgemeine Hygiene und Umweltmedizin

Confirmation of the Sterility of Terminally Sterilized Medical Devices

There is no doubt that the development of sterilization procedures for medical devices is a breakthrough in creating the indispensable working conditions of modern surgery. It is thus a prerequisite for the further refinement of surgical methods. The epoch-making developments in surgery was only feasible when we became able to work under strictly aseptic working conditions. It was the application of the steam sterilizer (Trendelenburg, 1882), the aseptic procedure in surgical wound treatment (Kurt Schimmelbusch, 1892) and the provision of steam sterilizers according to the specifications of Robert Koch in the Berlin Charité in about 1890 that sparked off this epoch-making change.

In the new era, sterilization was initially performed in the immediate vicinity of the surgical tract with its high standard of clean-room conditions. However, for about 50 years sterile materials have been increasingly manufactured as disposable products throughout the world and traded over very great distances between the continents. The specifications for the barrier effectiveness of sterile packaging have risen very substantially because the duration of storage has been extended to five years in most cases and also because of extreme transport conditions such as temperature fluctuations, transport over regions at different altitudes or storage in depots with extreme climatic variations.

These changes in conditions of storage and transport in past decades mean that the following consideration has become of crucial relevance for the quality of sterile products: most commercial packages are partially permeable (porous) in compliance with ISO 11607-1 or have porous components which enable the penetration of the sterilizing agent (steam, gas). They maintain the "sterile" state only when their filter characteristics meet the high requirements during transport and storage. Therefore, the barrier effectiveness of sterile packaging should be unequivocally specified on the packaging in order to ensure that the attainable sterility standard of the product concerned is not lost owing to an inadequate barrier function of the packaging.

From the viewpoint of the practicing clinician, the following information is urgently required in order to deal with sterile materials: the calculated barrier effectiveness must be specified on the packaging of the sterile material.

In accordance with the international standard ISO 11607-1 dating from 2006, the barrier effectiveness is ascertained in a defined testing procedure. This results from the ratio of the exposure to a microbial aerosol in the flow experiment to the amount of microbial contaminants that pass through the packaging. The barrier effectiveness determined and thus the filter characteristics of the packaging can in this way be specified as a decimal-logarithmic reduction of the microbial count. The sterility of the transported and stored product can be critically appraised solely on the basis of this parameter. In hermetically sealed packages, on the other hand, the documentation of impermeability fulfills the specification for the microbial barrier (ISO 11807:2006)

The sterile state of a packed product can be readily confirmed to be on the requisite high sterility level of EN DIN 556 (theoretically one nonsterile product out of million packaging units) when the specification of the barrier efficacy is checked against the actual microbial demands of transport and storage. You are referred to our new internet site www.microbial-evaluation-of-sterile-barrier-systems.com