Sterilization succeeds only with appropriate pre-disinfection and cleaning

The reprocessing of reusable medical devices remains a complex and challenging task that requires compliance with strict procedures and regular updates to reflect the latest scientific and technological advancements.

Interestingly, the European Standard for small steam sterilizers EN 13060 in §3.35 specifies:
“The presence of a viable microorganism on any individual item can be expressed in terms of probability. This probability can be reduced to a very low number, it can never be reduced to zero”.

A crucial but often underestimated factor in achieving sterile instruments is the pre-disinfection and cleaning process, which significantly reduces the initial microbial contamination and brings the process closer to "probability zero."

Over the past decade, my observations from teaching reprocessing practices to numerous dental assistants has revealed that many clinics struggle with efficiently performing key phases, particularly pre-disinfection and cleaning. This inefficiency often stems from a lack of awareness among both staff and dentists about the crucial importance of these early steps. Even though modern sterilization technologies, such as medical-grade type B cycles, are indispensable for achieving sterile instruments, they alone cannot guarantee sterility without proper pre-disinfection and thorough cleaning beforehand. Deficiencies during these preliminary stages can have serious consequences for patient and staff safety, increasing the risk of injury or infection.

This article aims to highlight common mistakes in reprocessing workflows focusing specifically on predisinfection and cleaning and provides practical solutions to elevate performance to "best practice" standards, comparable to hospital-grade protocols. I also noticed and therefore want to emphasise the confusion in using the term “decontamination”.

(ISO/DIS 11139:2017 / 3.27 bio-decontamination: removal and/or reduction of biological contaminants to an acceptable level.)

According to the international standard ISO 11139, "decontamination" refers to the removal or reduction of biological contaminants to an acceptable level. However, in practice, the term is frequently misinterpreted as a synonym for pre-cleaning, cleaning, or even the entire reprocessing workflow. To avoid confusion, each step in the reprocessing cycle should be clearly defined and named: pre-cleaning, cleaning, disinfection, maintenance, packaging, sterilization, and storage.

Each step plays a crucial role in reducing microbial contamination, and the term "decontamination" should not be used as a catch-all term for these processes. Clear terminology helps improve understanding, ensures correct implementation, and facilitates proper documentation of procedures.

When should pre-disinfection occur?

All used and non-used instruments must be immediately soaked after treatment and throughout the procedure (burs and files) if extended. This will prevent blood, saliva, and debris from drying, which could restrain the efficiency of the following cleaning phase. Many guidelines underline the soaking baths must be in the operating room.

Note: This article does not concern handpieces, which should obviously be processed following the same phases as other instruments. However, they are more specific, e.g. they cannot be soaked and cleaned ultrasonically. They are also more challenging due to their unique design.

Which kind of disinfectant is appropriate?

Disinfection is defined as “a process to inactivate viable microorganisms to a level previously specified as being appropriate for a defined purpose” (ISO/DIS 11139:2017-3.36). Presented this way, it doesn’t really help dentists or dental assistants to acquire the appropriate disinfecting solution.
The objective of this initial phase is to reach an intermediate level of disinfection. The expected broad spectrum is illustrated in figure 1.

The disinfectant data sheet often indicates different dilution rates and/or exposure times according to the resistance of microorganisms, which might confuse the user and impede reaching the required disinfection level. To avoid that, the highest concentration and the longest soaking/contact time must be considered.

Note: A disinfectant can claim “fully virucidal” only if it inactivates both enveloped and non-enveloped viruses which offer a different resistance, as illustrated. Ideally, the disinfectant must feature a broad spectrum without compromise (!), with the lowest dilution rate and the shortest exposure time.
A dilution rate of 2% with a contact time of 15 minutes is rational.

Note: The purchase of such disinfectant often comes down to price, but unquestionably without compromising the expected impact! The real price to be considered is the cost per litre of the solution prepared. A disinfecting solution featuring a dilution rate of 2% vs 4% is 50% more economical even if, at first glance, it might be slightly more expensive. In the end, we are talking about less than one € per litre, which is “ridiculous” and priceless considering the safety and health of staff!

How should the disinfectant featuring a 2% dilution rate be prepared?

It seems obvious at first glance, but I recognised many users miscalculate the amount of concentrate and/or water to be mixed. This is probably because the concentration rate is usually expressed in percentage, e.g. 2%, which equals to 2 ml of concentrate per 100 ml of disinfecting solution.
I recommend multiplying by 10, which relates to 20 ml per 1,000 ml (1 litre). The preparation of a 3-litre soaking bath requires 60 ml (3 × 20 ml) of concentrate completed with 2,940 ml of water (not 3,000 ml!).

How often shall the disinfecting solution be replaced?

Minimum once a day. Every morning, a new disinfectant solution must be prepared in a cleaned soaking bath from the evening before. Then, it should be replaced whenever the solution is turbid. Considering the impact of this step, the solution must be kept clean and effective throughout the whole day.

Are there other potential typical mistakes that should be avoided?

Apart from selecting the wrong product and failing in preparing (diluting) the solution, there are several additional mistakes which would impede pre-disinfection and expose staff to risk.

What is the following step?

After pre-disinfection, the abundant rinse of the instruments with (hard) tap water aims to remove residual chemicals, particularly in hollow and hinged items. Chemical residues could lead to irreversible staining and damage to instruments should a thorough rinsing step be missed.

And … cleaning?

The cleaning step prior to disinfection and sterilization is crucial. Proper cleaning is the foundation of the entire reprocessing cycle and is fundamental for safe sterilization. As stated in most guidelines: "only clean instruments can be sterilized".

Instruments must be visually free from organic residues, mineral deposits, debris, and stains prior to sterilization as these present an obstacle to steam. Appropriate cleaning additionally contributes to reducing the microbial contamination and get closer to “tolerance zero”. As illustrated by the Sinner Circle, cleaning involves four factors: temperature, time, chemical and mechanical actions, interacting in variable proportions. If one factor is reduced, the loss must be compensated by increasing one or more of the other factors.

Let’s focus on the mechanical factor, which plays a major role. It generates friction and pressure, i.e. the force needed to remove dirt as well as renewing the cleaning solution in contact with the instruments. If no equipment is used, the operator performing the manual cleaning is exposed to aerosols and a high risk of injuries. This manual cleaning method is considered as outdated by many guidelines, thus the least efficient. It is also challenging to demonstrate and record the efficiency and reproducibility of this method.

Modern technology offers automatic equipment capable of guaranteeing results. The use of a validated cleaning process, according to the EN ISO 15883-1/5, releases the doctor’s responsibility, which is “priceless”. The operator just “presses the cycle button”!

The thermal washer disinfector (TWD) features a final rinsing phase at 93°C, thus the thermal disinfection which additionally reduces the microbial count of the load. Often users think this post cleaning disinfection substitutes the initial pre-disinfection, NO! The use of a TWD does not exempt the user from the chair-side pre-disinfection. Last, but not least, the TWD fully dries the instruments inside and outside, ready to be pouched and B-type sterilized.

Conclusion

Considering the numerous mistakes highlighted in this article, I would be thrilled if every reader found potential and satisfaction to improve; got to source the right disinfectant offering a broad spectrum, including fully virucidal and mycobactericidal, as well as understood the dilution rate to get the soaking bath accurately prepared. Whilst addressing the few other mentioned potential mistakes, the initial predisinfection phase will contribute to the efficiency of the overall reprocessing process. The subsequent use of an automated and validated cleaning process will further rise the level of performance, brought closer to “best practice”.

As we are, you too should be motivated to “Getting it Right”.

Biography

Christian Stempf has worked extensively within the European dental industry. He has been involved in infection prevention for 30 years, with focus on reprocessing reusable medical devices, in particular sterilization and design of reprocessing areas. He has gathered valuable practical knowledge and experience through his daily activities and contacts with healthcare professionals and experts in the field of infection prevention throughout the world. He is a member of the European (CEN-TC102) normalization committee participating to two working groups i.e. steam sterilizers and washer disinfectors and he co-developed a high-end B type sterilizer. Christian offers vendor independent lectures for healthcare professionals as well as comprehensive courses for dental assistants worldwide.