Why Disinfection Remains the Gold Standard for Reprocessing Semi-critical Flexible Endoscopes

The buzz around liquid chemical sterilisation and ISO 14937

In contrast to disinfection, sterilisation is defined as a “validated process used to render product free from viable microorganisms” ⁴ This means that the process of sterilisation 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 ⁵ . In general, the preferred sterilisation method for medical devices is steam sterilisation 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 ¹ .

Why liquid chemical sterilisation does NOT mean your endoscope is sterilised
In other regions of the world, such as the U.S., sporicidal disinfectants are also called sterilising 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” ⁶ , ⁷ . However, within the context of disinfection, the term sterilant is misleading, as disinfection and sterilisation are two distinct methods. This becomes clearer when evaluating liquid chemical sterilisation (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 ⁶ . However, when used in conjunction with an EWD, there is no specific sterilisation standard to comply to. The EWD manufacturers may use the ISO 14937 standard ¹⁰ . This international standard specifies general requirements for a sterilisation process by physical and/or chemical means of packaged medical devices (in case no other standard for a particular sterilisation 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 sterilisation efficacy studies differ significantly from disinfection. Sterilisation 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 sterilisation. 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.

Disinfection: An unrivalled reprocessing process

Several attempts to improve disinfection have been made, including methods such as double HLD (DHLD), HLD plus an additional sterilisation using ethylene oxide (ETO) gas and LCS – which is common in the U.S.. Despite disinfection remaining the gold standard for endoscope reprocessing, in 2015, the U.S. Food and Drug Administration (FDA) suggested that implementation of supplemental measurements, such as LCS or DHLD, may increase the safety of reprocessed duodenoscopes ¹¹ .

But evidence from recent studies demonstrates that the aforementioned methods do not provide greater hygiene safety levels when compared with disinfection processes. For example, a study published by Gromski et al ¹² compared DHLD with LCS. The results of a hygiene test from almost 900 duodenoscopes resulted in low rates of positive cultures, demonstrating that the use of LCS for the reprocessing of duodenoscopes does not improve hygiene or impart any additional safety.

An additional study evidenced that DHLD processes offer no added benefits when compared with standard HLD processes ¹³ . Moreover, a comparison of duodenoscopes reprocessed by HLD, DHLD, or HLD plus ETO gas sterilisation found no significant differences between these groups in terms of bacterial contamination ¹⁴ .

Taken together, these studies indicate that a routine single disinfection process - the current gold standard for reprocessing - is effective.

A complete solution for flexible endoscope reprocessing

Olympus is committed to infection prevention, with an extensive range of products to support healthcare staff with their reprocessing protocols. Disinfection using an automated EWD, such as the Olympus ETD Mini, ETD4 and ETD Double, achieves reduction of all relevant microorganisms to prevent transmission of infectious agents. Customers can benefit from our Olympus process chemicals (PAA and EndoPro PAA) with bactericidal, fungicidal, mycobactericidal, virucidal and sporicidal activity that offer a high level of patient safety and handling safety for the operator, complying with all relevant European standards.

Summary

Effective reprocessing is mandatory to ensure medical instruments remain safe to use and to prevent the transmission of pathogenic microorganisms. While attempts are being made to advocate for LCS and DHLD in the U.S., numerous studies have argued that such methods have no significant impact on microbial growth and transmission potential. In fact, there is no published data to date that demonstrates that LCS of endoscopes offers a better outcome over routine disinfection ¹² .

Indeed, it is important that each step of the reprocessing process, including precleaning and manual cleaning, is carried out properly to ensure a successful disinfection of semi-critical flexible endoscopes – for unrivalled patient safety.