Sterilization of Health Care Products – Microbiological Methods
Bacteria and other microorganisms are plentiful, more so than many of us like to think. While estimates have varied, there are at least several tens of thousands of species of bacteria living on Earth, and there could potentially be hundreds of thousands or even millions. The natural ubiquity of these microbes means that microorganisms form colonies all over an animal’s surface tissues, such as its skin and mucous membranes. The normal flora of humans consists of mostly bacteria, with some eukaryotic fungi and protists.
However, the internal tissues of a healthy animal are normally free of microorganisms. In the health care industry, this and numerous other concerns necessitate sterilization, the process by which environments and health care products are made suitable for interface with patients.
A sterile health care product is one that is free of microorganisms. Therefore, for the process of sterilization—best described by the exponential relationship between the surviving microorganisms and the extent of the treatment with the sterilizing agent—to be successful, the presence and nature of bacteria and other microorganisms needs to be sufficiently estimated.
The ANSI/AAMI/ISO 11737-1 Standard
ANSI/AAMI/ISO 11737-1:2018 provides guidance on the enumeration and microbial characterization of the population of viable microorganisms on or in a health care product, component, raw material, or package. It is not applicable to the enumeration of viral, prion, or protozoan contaminants, and the standard does not apply to the microbiological monitoring of the manufacturing environment of health care products.
There is always some probability that a microorganism can survive regardless of the extent of treatment applied. It is crucial to characterize the probability of survival of the microorganisms present. ANSI/AAMI/ISO 11737-1:2018 takes an approach through the concept of “bioburden.” This describes the population of viable organisms present on or in a product and/or a sterile barrier system.
Bioburden is the sum of the microbial contributions from numerous sources, including raw materials, manufacturing, assembly processes, manufacturing environment, assembly aids, cleaning processes, and packaging of finished products. By directing attention towards these processes, bioburden can be useful for validating sterilization processes, control of manufacturing processes, monitoring raw materials or components, assessing the efficiency of cleaning processes, and an overall environmental monitoring program.
Changes to ANSI/AAMI/ISO 11737-1:2018
Please note that this American National Standard is an adoption of ISO 11737-1:2018, which was developed by ISO Technical Committee 198, Sterilization of health care products. The United States is one of the ISO members that took an active role in the development of this standard, and U.S. participation in ISO/TC 198 is organized through the U.S. Technical Advisory Group to ISO/TC 198, administered by the Association for the Advancement of Medical Instrumentation (AAMI).
- Added term “bioburden spokes” as a normal and consistent part of the bioburden, with examples.
- Clarified that package testing is not typically done unless it is an integral part of the product.
- Added information on the most probable number (MPN) technique.
- New details on ways to improve limit of detection (LOD).
- Removed some discussion of statistical methods for evaluating bioburden data where information was not typical or not required.
- New table for the criteria for selection of a bioburden recovery efficiency approach.
- Explained the use of the correction factor (CF).
- Eliminated bioburden efficiency value of <50% for technique modifications.
- Provided more information on the application and performance of a bioburden method suitability test.
- New section for direct plate counts, estimated counts, and counts beyond the ideal range.
- New table clarifying where typical responsibilities reside for the manufacturer or the laboratory.
- Increased focus on a risk-based approach.
ANSI/AAMI/ISO 11737-1:2018 is not the only ISO standard adopted by AAMI. In fact, there is another standard in this series adopted by the ANSI-accredited standards developing organization devoted to medical devices: ANSI/AAMI/ISO 11737-2-2009 (R2014) – Sterilization of medical devices – Microbiological methods – Part 2: Tests of sterility performed in the definition, validation and maintenance of a sterilization process
You can find other AAMI sterilization adoptions here: ISO Health Care Product Sterilization Standards Adopted By AAMI