Cleaning & Disinfection

Objectives of cleaning and disinfection

Cleaning is intended to remove soils (e.g., patient secretion, tissues and inorganic material such as salts) from surfaces of reusable medical devices (RMD). Cleaning also helps remove some of the microbial load and limits the amount of endotoxin or pyrogen residue that may remain after sterilization.

Disinfection reduces the microbial burden.

When disinfection is thelast step before use of an RMD, its objective is to render the RMD safe for the patient according to Spaulding classification
When disinfection is performed in preparation for sterilization (for example in automated washer-disinfectors), disinfection improves the preparation of a RMD and may be required or recommended in some countries as an occupational health and safety measure for operators in charge of packaging.

This chapter will first serve as a reminder of the objectives and principles of cleaning and disinfection before describing the various types of cleaning and disinfection processes (manual, automated, and ultrasonic cleaning) and their implementation. See flexible endoscopy for the reprocessing of thermolabile endoscopes.

Objectives and principles of cleaning

Cleaning consists of washing followed by rinsing

Washing is the removal of contaminants from all surfaces of the RMD by water containing a cleaning agent.
Rinsing evacuates the soils detached by washing as well as detergent residues, which would chemically interact with disinfection or sterilization agents.

The conditions for efficient washing are illustrated by the Sinner circle

Mechanical action by manual brushing, flushing, swabbing or wiping, automated spraying or flushing, cavitation (in ultrasonic cleaner).
Chemical action of cleaning agents which decompose protein, fats, ease the removal of soil from surfaces.
Contact time of all RMD surfaces with the cleaning/water solution.
Temperature of the cleaning solution..

Consistency of cleaning (i.e. rigorous application of cleaning procedure after each use of the RMD) is key to avoid the progressive formation of biofilms or build-up of mineral deposits in narrow spaces or cavities

Once installed, biofilms (for instance biofilms of Pseudomonas aeruginosa) protect the germs from disinfection agent. Biofilms are likely to grow and become more difficult to withdraw even if the next cleaning is well performed.

Build-up of mineral deposits (for instance scale) eases the anchorage of germs and biofilms, damages instruments and impairs their functionality.

Main categories or detergent are : neutral, with or without enzymes, mild alkaline with or without enzymes, alkaline

Most detergent formulations include a surfactant (to reduce the surface tension of water thus easing the wetting of surface and breaking up of soils).
Other components of detergents are Buffers to improve the compatibility with RMD material and Softeners to reduce the potential negative effect of hard water (spotting and deposit on surface).
Neutralizers may be applied after some alkaline cleaners.

Cleaning agent must comply to applicable local detergent regulation. Methods and thresholds are available to evaluate cleaning efficacy of processes (see international standards)

Objectives and principles of disinfection

Disinfection process is adapted to the level of risk of the procedure as defined by Spaulding classification (low, intermediary or high level disinfection) and adapted to the type and quantity of mircroorganisms which may be present on the RMD. Additional precautions may be required in special circumstances (for instance a C. Difficile breakout).

One step manual cleaning and disinfection with a cleaning & disinfection agent might be considered sufficient for low risk RMD according to Spaulding classification or in some cases for preparation before sterilization.

Unlike sterilization, which targets eradication of all microorganisms, disinfection claims are by category of microorganisms (bacteria, fungi and yeast, viruses, mycobacterica, spores) and characterized by the achievement of a specified log₁₀ reduction on predefined test microorganisms.

Categories of microorganisms are listed below in order of usual growing order of resistance to disinfectant (examples of microorganisms frequently used for tests appear in brackets):

Vegetative bacteria: gram negative and gram positive (for examples, Staphylococcus aureus, Pseudomonas aeruginosa)
Fungi/yeast (Aspergillus niger, Candida albicans)
Virus: enveloped (lipid or medium size) viruses such as HIV, herpes, hepatitis are less resistant than bacteria while non-enveloped (nonlipid or small viruses such as polio).
Mycobacteria (M. tuberculosis, M. terrae, M. avium)
Spores (Bacillus. atropheus, B. subtilis, B. cereus, Clostridium sporogenes)

Each claim (bactericidal, fungicidal, virucidal, mycobactericidal, sporicidal) is validated separately. A successful sprocidal test does not avoid a test with microorganisms of lower resistance.

Unlike for sterilization, there is no unique ISO international standard for evaluation of disinfecting activities. Tests protocols are hence subject to regional variances (AOAC or ASTM in USA, CEN in Europe).

Tests microrganisms are protected by artificial soil that simulates the level of organic matter which may be found on RMD.

Disinfectants used after cleaning are commonly tested in clean conditions (low amount of artificial soil). Disinfectants used for combined cleaning and disinfection are tested in dirty conditions (high amount of artificial soild).

Disinfection is chemical or thermal

Chemical disinfection is performed with a disinfection or cleaning & disinfectant formulation. All RMD surfaces must be exposed to the disinfecting formulation at concentration, temperature and for the contact time specified by the disinfectant manufacturer instructions for use (IFU).

Chemical disinfectants formulations are aldehydes (Glutaraldehyde, Ortho-phthalaldehyde-OPA) and peracetic acid. Detergent-disinfectants use chemical with dual properties or mixtures of detergent and disinfectant.

Aldehydes have strong compability with RMD. Room ventilation is required for glutaraldehyde due to irritancy and potential toxicity.

Ortho-phthalaldehydes (OPA) are better tolerated.

Aldehyde are fixative of protein and must be only be used after thorough cleaning. Formaldehyde which also belongs to the aldehyde disinfection family is a carcinogen and not anymore used.

Peracetic acid (PAA) has a broad spectrum of activity and strong efficacy on spores but is less stable and more corrosive than aldehydes. PAA decomposes in water and acetic acid (vinegar) and more environement friendly than aldehydes.

Other formulations based on hydrogen peroxide, chlorine based, chlorine dioxide (ClO₂) may be found. Compatibility with materials of RMDs must be checked.

Alcohol is not an effective disinfectant for RMD (it does not penetrate well into organic material, not sporicidal and protein fixative in some conditions).

Combined cleaning and disinfecting chemical formulations are mixtures of quarternary ammonium, biguanide, guanidine, alkylamine, enzymatique, alkaline. Aldehyde based cleaner-disinfectant are avoided due to their fixative properties.

Choice of formulation might be influenced by local habits, recommendations or regulations, for instance in regards to protein (prion) fixative properties or for waste management considerations.

Thermal disinfection is commonly used for surgical instruments and reusable containers intended for steam sterilization and takes place in automated washer-disinfectors (see below).

Thermal disinfection has limited efficacy on spores; however, small quantities of spores not eliminated by cleaning and thermal disinfection will be eradicated by sterilization.

Thermal disinfection is achieved when all RMD surfaces have been exposed to hot water at a defined temperature for a minimum contact time. Thermal disinfection can be characterized by the A₀concept.

For a category of microorganisms showing similar resistance to hot water, log reduction can be predicted by a time/temperature relationship. For instance 10 minutes at 80°C has the same lethality effect as 1 minute at 90°C or 100 minutes at 70°C.

By convention, the time needed to achieve a targeted log reduction of highly heat resistant microorganism at 80°C is called A₀. (see A₀ formula below this note). A₀is expressed in seconds (for instance A₀ = 600 if the time required to reach the targeted lethality effect at 80°C is 10 minutes (10 x 60 s) . The A₀ concept applies for temperature above 65°C, but in practice most thermal disinfection works above 80°C.

Local regulations, recommendations or habits define the A₀ thresholds to be achieved according to the level of contamination of the RMD and intended use. A₀ of 60 s is commonly recognized as the minimum to be targeted for low risk items. 600 s is the minimum for other items and increased according to risk. Automated washer-disinfectors (WD) for surgical instruments complying to international standard ISO 15883-2 must have one cycle with an A₀ value above 3000 (e.g. a theoretical value of 50 minutes at 80°C or practically 5 minutes at 90 °C or 2 min and 30 s at 93 °C). However, local recommendation for high risk RMDs may be below or above 3000 s.

A₀ values of 3000 or above are recommended in some countries. Since thermal disinfection always takes place after cleaning and is often followed by sterilization, other countries consider 600 s to be sufficient on most items (small residual quantities of spores or heat resistant microorganisms, if any, being eradicated by sterilization).

A₀equation is as follows (See annex B of international standard ISO 15883-1 for more explanation)

A₀ = Σ10^[(T-80)/z] △t

A₀ is the A value for microorganisms with a z value is 10 (i.e. microorganisms for which an additional 10°C is needed to achieve an additional 1 log reduction by moist heat).

Thermal disinfection provides good drying.

Thermal disinfection also contributes to the self-disinfection the washer-disinfector (thereby limiting the risk of cross contamination between loads).

Choice of cleaning & disinfection process

International standards reminds that the medical device manufacturer must provide instructions for reprocessing.

International standard ISO 17664 says :

At least one validated automated cleaning method (which may include a validated manual pre-cleaning method) shall be specified unless the medical device cannot withstand any such process, in which case a statement shall be provided which alerts the user to this issue……. A validated method of manual cleaning shall be specified if automated cleaning is not possible.

if the medical device is intended to be disinfected, at least one validated automated disinfection method shall be specified unless the medical device cannot withstand any such process, in which case a statement shall be provided which alerts the user to this issue…… If the medical device is intended to be disinfected a validated method of manual disinfection shall be specified if automated disinfection is not possible

International standards do not assign responsabilities but typical roles are as follows:

RMD manufacturer IFUs specify the cleaning and disinfection methods after verifying that the RMD can be efficicently cleaned, disinfected and remains functional and safe for use. If needed, the IFU indicates a maximum number of reprocessings allowed.
WD and ultrasonic cleaner manufacturers recommend the type of detergent and disinfectant approved and tested for use with their equipment.
Cleaning and disinfecting agent manufacturers indicate whether the chemistry is intended for manual, automated or ultrasonic cleaning and provide dosage, contact time, T°C, water quality for each type of usage. Precaution for use, waste management, and time during which an open detergent or disinfectant bottle can be used are provided. Labeling carries the expiry date.

Cleaning and disinfection processes are manual or automated

Manual cleaning & disinfection: RMDs are immersed and manually processed in separated cleaning and then disinfection baths. Manual reprocessing may be assisted by pumps that are connected to channels that flow detergent and disinfectants at preset rates in channels. When immersion is not allowed by RMD manufacturer IFU, RMD is wiped.
Automated washer-disinfector: Disinfection is chemical or thermal (see above). Ultrasonic cleaning may be used to prepare automated washing-disinfection of complex or heavily soiled RMDs. Thermosensitive flexible endoscopes are reprocessed in Automated Endoscope Reprocessors (AERs).

When possible, automated processes are preferred to manual

Washer-disinfector (WD) and automated endoscope reprocessors (AER) are more reproducible (less human dependant) and safer for operators (reduction of exposure to chemicals, aerosols, handling risk) and automatic recording allows reliable documentation.

For cleaning and disinfection of RMD in preparation for steam sterilization thermal disinfection is preferred

ISO 15883-1 says: Thermal disinfection processes are more easily controlled and avoid the hazards to staff, patients and the environment that can occur through the use of chemical disinfectants. “Thermal disinfection is efficient to eliminate most microorganisms (except spores) and provide good rinsing and drying.”

Implementation of manual cleaning & disinfection process

The standard operating procedure (SOP) for manual cleaning & disinfection are defined according to the instructions for reprocessing of the medical device manufacturers and instructions for use of the detergent, disinfectant and cleaning accessories manufacturers.

The SOP details each step of the process.

Water quality (hardness, pH) and temperature and preparation of cleaning and disinfection baths are specified. The disinfection bath is preferably single use. If not, the maximum number of reuse specified by the manufacturer of the disinfectant is respected and means are provided by the manufacturer to control that the concentration of disinfection agent is above minimum levels required for efficacy.
Brushes, single-use cloths and other cleaning accessories to be used are described. Soft (nylon) bristle brushes are usually advised. Unless clearly specified in the RMD IFU, metallic brushes are not used.
Type, size (diameter and length), bristle type and material of lumen brushes are defined. They should be the same diameter as the lumen to ensure that all internal surfaces can be reached and long enough to exit the distal end of the instrument. If not single use, brushes are cleaned, disinfected (preferably thermal) and dried at the end of the day. Brushes are checked after each use and replaced when damaged. SOPs specify how and how many times each channel must be brushed. Manufacturers may have special recommendation for cleaning of optics.

Manual cleaning steps are as follows:

The RMD is completely immersed in the cleaning bath. Articulated RMDs are open to minimize mated surface area. Bubbles which may be trapped in cavities and channels are eliminated. Some manufacturers may recommend flushing through at a specified pressure for a defined time. RMD remains immersed during cleaning. Cleaning operations are performed in a manner that limits production of aerosols or dispersion of potential contaminated chemicals or water.
Gross soil is removed. Accessible surfaces are cleaned with appropriate tools until visibly cleaned. RMD with articulations are moved (opened and closed at least 5 times). Channels are swabbed at least 5 times. Other clean areas that are hard to access are flushed with a syringe, water gun or hand pump. Swabbing is always performed in the same direction from the less soiled to the most soiled end.
RMD is rinsed under running water (at least 10 s for all external surfaces). Articulations are moved. Channels are flushed for at least 10 s. RMD is allowed to drain to avoid dilution of disinfection solution. Rinsing removes visible or non-visible soil as well as residual detergent which might react with the disinfectant.
RMD is visually controlled. RMD and canulated device are placed on a white clean surface (for instance white crepe paper) and observed under illuminated magnifier.
RMD is immersed in disinfection bath. Articulations are moved at least 5 times. It must be checked that internal lumen and cavities and completely immersed and in contact with solution.
RMD is rinsed with appropriate water quality: 10 s at least for all external surface and 10 s flush for each channel.
RMD is dried with compressed medical air. If not available or not recommended by the manufacturer of the RMD, compressed air drying is replaced by air dry or hand-dry using a disposable clean, non-linting cloth.

In some countries, manual cleaning and disinfection procedures are defined according to device configuration.

For instance in Germany RMD are ranked in 3 categories (simple, RMD with hinges, RMD with lumen).

RMD which cannot be immersed (for example some motors, batteries) are wiped and rinsed with disposable cloth soaked with detergent and/or disinfectant agents. Manual wiping is used when non other cleaning and disinfection methods are applicable. Manual wiping is carried according to RMD manufacturer IFU.

Wipe with a disposable clean, non-linting cloth and detergent until all cleaning agent residue is visually removed. Check that moisture does not penetrate into critical parts of the device (for instance power or electronic connections).
Rinse the RMD by wiping surfaces thoroughly with a damp, disposable, clean, non-linting cloth with objective to withdraw disinfection residues.
RMD is visually controlled if needed with an illuminated magnifier.
Dry with medical-grade compressed air. If compressed air is not available or not recommended by the manufacturer of the RMD, air dry or hand-dry using a disposable clean, non-linting cloth. Disposable cloths are discarded.

If wiping is performed with a cleaning & disinfecting agent (non-critcial RMD only), steps 2 and 3 are eluded.

Implementation of ultrasonic cleaning process

Ultrasonic cleaners (US) withdraw soils from the surface of RMDs by cavitation.

Ultrasonic cleaning is used only if not contraindicated by RMD IFU.

In practice, ultrasonic cleaners are used for pre-cleaning (prior to washer-disinfector) of complex stainless steel RMDs with reamers (rasps), lumen, sleeves or shapes difficult to access.

Ultrasound generators produce acoustic waves (waves frequency generally ranges between 35 and 45 kHz). Acoustic waves create bubbles which implode as they become larger and unstable. Implosion creates a vacuum in the solution (cavitation) that mechanically draws debris from the surface of the RMD.

Efficacy of cavitation improved by adapted cleaning agent.

Ultrasonic cleaners encompass a wide range of technologies from the basic ultrasonic cleaning equipment with the user performing all the functions of filling, rinsing, draining to automated equipment. Ultrasonic cleaners could be categorized as follows: (basic) ultrasonic cleaners, ultrasonic irrigators or irrigator-washer or irrigator washer-disinfector.

Ultrasonic cleaning is not recommended for RMD with:

Some types of adhesives
Mixing different metals (for instance scissors with screw, needle holder, clamps with jaws in tungsten carbide, chrome or nickel steel)
Optics (because of the risk for adhesives and seals)
Power tools

Other active items such as phacoemulsification or dental handpieces

Principles for preparation of ultrasonic cleaning SOP are as follows:

Follow instructions of ultrasonic cleaner and detergent manufacturers for dosing and temperature of bath. Water temperature is between 27 °C (80 F) and 43 °C (109 F) and never above 60 °C (140 F) because most proteins denature above that temperature. For ultrasonic systems without thermoregulation, room temperature might be preferable as energy delivered by ultrasonic waves will increase the temperature of the bath. Detergent, if used, is adapted to ultrasonic cleaning and dosed accordig to IFUs.
The bath is degassed at each filling. This is done by filling the unit, closing the lid and running a cycle for 5 to 10 minutes
Before immersion, soil is removed from device. RMD is placed in a tray (never directly on tank end) widely opened, not superposed to avoid shadow. When applicable, connect lumen devices to flushing ports. If other specific positioning accessories and features are used, refer to manufacturer IFU.
The cavitation process may create aerosols, so the ultrasonic bath should have a lid that must remain closed during the cleaning process.
Process time is as recommended per manufacturer (usually between 5 and 10 minutes).
If rinsing is not performed by the ultrasonic cleaner, the RMD is rinsed and dried manually.

The bath is preferably changed after each use (i.e. after reprocessing cycle). Ultrasonic cleaning equipment is cleaned every day that it is used and according to manufacturer IFU. Local recommendations specify that the bath must be refilled after each use or daily and each time the bath is visibly soiled.

National regulations or recommaendations may forbid the use of ultrasonic cleaners if a prion risk has been identified.

Implementation of washer-disinfector processes

Washer-Disinfectors (WD) spray or flush pressurized water mixed with a detergent on surfaces of RMD and lumen. The cleaning stage is followed by a thermal or chemical disinfection.

Various types of WD and applicable international standards are as follows :

Washer-disinfectors with thermal or chemical disinfection stages for surgical instruments. They are available in different construction, e.g. single chamber (load-through or single door) or multichamber version.
Thermolabile endoscope washer-disinfector. See flexible endoscopy.
Cart-washer for the cleaning of carts, reusable containers, surgical basins and other non-invasive, non-critical medical devices.
Multichamber washer-disinfector.
Washer-disinfector for dental handpieces and turbines

ISO 15883 group of International Standard includes general requirements ISO 15883-1 and specific parts dedicated to each type of WD.

WD for instruments comply with ISO 15883-1 and -2
WD for thermolabile flexible endoscope comply with ISO 15883 -1 and – 4
Cart washer comply with ISO 15883-1 and -6 (thermal disinfection) or – 7 (chemical disinfection)

There is currently no ISO standard for dental handpieces and turbines

Washer-Disinfector (WD) process SOP:

Identifies or raises attention on medical devices that may require ultrasonic precleaning.
Reminds RMD manufacturer recommendations for device preparation: disassembly, removal of cap, gaskets and all disposable items, opening (generally at 90° of hinged surgical instrument with handles (scissors, clamp, and forceps).
Define the load configuration (i.e. the type of RMD which can be reprocessed together in a given cycle).
Specifies how RMDs are properly placed in the WD:

RMD are placed in a tray or positioned on suitable modules and/or connected to irrigation ports (for lumen devices).
If needed, hold down screens or retaining systems to prevent dislodging of RMD during the cycle.
Fragile or small devices are protected (installed in trays with lid and/or blocking accessories).
Heavy or large items are preferably placed on lower-levels.
Hollow items are turned downwards to allow water evacuation.
Racks should never be overloaded. All RMD surfaces must be exposed to water spray (no shadowed surface).
Specialized racks and loading equipment are required for RMDs with complex geometries and lumen. Racks, for instance, are available for laparoscopic surgery, dentistry, robotic surgery.
Minimally Invasive Surgery (MIS) instruments with lumen are connected to adaptors. Adaptors are carefully chosen for proper flushing pressure and flow. Clear procedures are key to optimize the layout, avoid connection mistakes or accidental disconnection during cycles. In case of especially narrow lumens, a filter is required to prevent particles from entering the lumen.

Cycle is selected according to the load. Before cycle launch it is checked that spraying arms are unobstructed.
All phases of WD cycles are automatically run, controlled and recorded.

Pre-washing wets the RMD (without detergent) to ease soil removal.
Washing is at temperature specified by detergent manufacturer (usually around between 45 °C. Mechanical action is by spray, circulation or irrigation). Cleaning solution is single use.
Intermediary rinsing may include a neutralization stage (for some cleaning agent formulations).
Thermal (preferred if applicable) or chemical disinfection is adapted to contaminants and log reduction targets. In chemical WD, if the disinfection is not single use, the maximum number of reuse specified by the disinfectant manufacturer is respected. Recommendations and means are provided by the manufacturer to control that the concentration of disinfection agent is above minimum levels required for efficacy.
Final Rinsing. In thermal WD, thermal disinfection also serves as a rinsing phase.
Drying is obtained by circulation of hot air (of appropriate air quality).

Cleaning & disinfection and quality management

Cleaning & Disinfection processes are defined, validated and implemented in accordance with quality management and process validation principles:

Washer-disinfector, ultrasonic equipment are installed in accordance with manufacturer recommendations. Instructions for use and certificate are available. It is verified that equipments operate as intended and that processes meet cleaning and disinfection expectations.
Updated Standard operation procedures (SOP) are available.
Routine controls are specified.
Occupational health & safety measures are in place (in particular exposure to liquid and vaporized chemicals, aerosols and injuries by potentially contaminated RMD)
Reprocessing fluids are discarded according to local waste management rules.
Training on SOP, routine controls, occupational health & safety and waste management take place and knowledge are periodically controlled
Maintenance plans are in place for washer-disinfector, ultrasonic cleaners and dosing pumps.
Traceability is operational.

WFHSS key recommendations for cleaning & disinfection

Cleaning is key for efficient disinfection or sterilization. Minimally invasive surgeries are often performed using devices with complex, narrow geometries, which are difficult to access and cannot be visually controlled. If cleaning is not performed with consistency, biofilms and mineral deposits may accumulate over time.
When disinfection is the final step before use of the medical device, disinfection level is in accordance with Spaulding classification principles (low, intermediate, high). When done in preparation for sterilization (for example in a washer-disinfector), disinfection improves RMD preparation and contributes to minimizing risk for packaging operators.
Automated cleaning and disinfection in a washer-disinfector is preferred to manual. Thermal WD are preferred for heat and moisture resistant RMD. When allowed by RMD manufacturer IFU, ultrasonic pre-cleaning is useful for devices with complex geometries.
Non automated cleaning & disinfection processes are performed with care and consistency by adequately trained operators. Wiping is used when RMD manufacturer IFU do not allow immersion. One-step manual cleaning and disinfection with a cleaning & disinfection agent might be considered sufficient for low risk RMDs according to Spaulding classification or in preparation for sterilization.
Manual and automated cleaning & disinfection processes are validated and implemented in accordance with quality management principles. Standard operating procedures are updated and executed by trained operators. Appropriate occupational health and safety measures and traceability are in place.

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