The buzz around liquid chemical sterilization and ISO 14937
In contrast to disinfection, sterilization is defined as a “validated process used to render product free from viable microorganisms”
This means that the process of sterilization eliminates microorganisms to near zero, which consequently means that process efficacy is measured as a probability termed SAL (Sterility Assurance Level). Typically, an SAL of 10-6 should be reached
. In general, the preferred sterilization method for medical devices is steam sterilization and the effectiveness of this method is well researched. However, it cannot be used for critical reusable flexible endoscopes used inside sterile body cavities due to heat- sensitive components that are easily damaged by the high temperatures
Why liquid chemical sterilization does NOT mean your endoscope is sterilized
In other regions of the world such as the U.S., sporicidal disinfectants are also called sterilizing agents/sterilants, and these are commonly associated with high-level disinfection (HLD). HLD is defined as a “complete elimination of all microorganisms in or on an instrument, except for small numbers of bacterial spores”
. However, within the context of disinfection, the term sterilant is misleading as disinfection and sterilization are two distinct methods. This becomes clearer when evaluating liquid chemical sterilization (LCS).
LCS was introduced for heat-sensitive devices and uses HLD disinfectants that are termed sterilants based on their sporicidal efficacy, e.g., when tested according to AOAC-966.048 (US) or TGA-1049 (Australia) (see table 1). When a device is subject to LCS, it is completely immersed in an active sterilant solution for a prescribed period of time (brand-dependent, up to 12 hours), at a controlled temperature and concentration
. However, when used in conjunction with an EWD, there is no specific sterilization standard to comply to. The EWD manufacturers may use the ISO 14937 standard
. This international standard specifies general requirements for a sterilization process by physical and/or chemical means of packaged medical devices (in case no other standard for a particular sterilization process exists).
In contrast to ISO 15883-4, ISO 14937 does not specify a number of key variables, including the test method, test microorganisms, and minimum spore reduction (see table 1). In addition, it is important to note that the testing conditions for sterilization efficacy studies differ significantly from disinfection. Sterilization efficacy tests are done under clean conditions only. When it comes to disinfection, compliance testing is simulating clean and dirty conditions and so offers a higher safety margin (as mentioned above).
In terms of defining the term “sterilant”, in Europe, chemicals that are used for automated disinfection are called disinfectants with sporicidal efficacy. In fact, reprocessing of endoscopes within an EWD cannot meet the conditions for sterilization. For example, even if a sterilant is used in an EWD, the water used for final rinsing and the air inside and outside of the machine are not sterile. Furthermore, sterile medical devices require specific preservation processes including appropriate sterile packaging and storage.