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Are Quaternary Ammonium Disinfectants Adequate?
By Lawrence F. Muscarella, PhD
Laryngoscopesare one of several different types of rigid and flexible endoscopes sometimesreferred to as ENT (or ear-nose-throat) endoscopes. Examples of flexiblelaryngoscopes include rhinolaryngoscopes and nasopharyngo-laryngoscopes.Rhino-laryngoscopes use fiber-optic or video technology to examine, diagnose andevaluate the normal physiologic and pathologic conditions of, among otherorgans, the larynx. Most models are used for diagnostic procedures and do nothave any internal channels. Some models, however, feature a single workingchannel, a suction control valve, and a biopsy inlet port that can be used foraspiration, removal of foreign objects, and performing biopsies.Naso-pharyngo-laryngoscopes are similar in design and function torhino-laryngoscopes. Rigid laryngoscopes, on the other hand, are used to exposeand view the larynx to facilitate endotracheal intubation. These endoscopesfeature a fiber-optic disposable or reusable blade that is available indifferent sizes, may be curved or straight and connects to the laryngoscopeshandle.
Classification of Medical Instruments
Before it can be determined whether selection of a quaternaryammonium product is appropriate for cleaning and disinfecting rigid and flexiblelaryngoscopes, it is first necessary to evaluate the risk of nosocomialinfection associated with the use of these instruments. Application of a widely accepted three-tiered classificationscheme for medical instruments aids in the evaluation of this risk. According tothis scheme, medical instruments that penetrate sterile tissue, enter thevasculature, or contact the patients blood are classified as criticalinstruments, because the risk of nosocomial infection associated with their useis high.1-4 (See Table 1.)
Semi-critical instruments, on the other hand, contactmucous membranes or non-intact skin, but do not typically penetrate steriletissue (see Table 1). The risk of nosocomial infection associated withinstruments in this second category, while still potentially significant, ismarkedly less than the risk associated with critical instruments.Rhinolaryngoscopes, naso-pharyngo-laryngoscopes, and the blades and handles of rigid laryngoscopes are classified in this secondcategory.1-4 Medical instruments that either do not directly contact thepatient or only contact a patients intact skin pose a low risk of nosocomialinfection and therefore are classified as non-critical instruments (seeTable 1).1,2 Most environmental surfaces, including walls, floors and sinktops, are included in this third and low-risk category.
Sterilization and the Three Levels of Disinfection
Once the risk of nosocomial infection associated with the useof rigid and flexible laryngoscopes has been evaluated and their classificationas semi-critical instruments understood, a review of: published endoscopereprocessing and infection control guidelines; the definitions of sterilizationand disinfection; and the labels of quaternary ammonium products is necessary todetermine whether they are sufficiently effective to satisfy the minimumreprocessing standards required to prevent rigid and flexible laryngoscopes (andother semi-critical instruments) from transmitting disease.
Whereas sterilization is an absolute term and refers to aprocess that destroys all types of microorganisms including high numbers ofresistant bacterial endospores, disinfection is a relative term and refers todifferent types of processes that vary in effectiveness. As displayed in Table 2in decreasing order of biocidal effectiveness, disinfection processes can beclassified into one of three categories, or levels: high-level disinfection(HLD), intermediate-level disinfection (ILD), and low-level disinfection(LLD).1-4 Each of these three levels of disinfection is, in effect, defined anddifferentiated from one another by specific indicator microorganisms thateach respective level can and cannot reliably destroy. The relativeresistance of microorganisms to sterilization and the three levels ofdisinfection is displayed in Table 3.1. The more resistant the microorganism,the higher the level of disinfection (or sterilization) required to destroy it.
Defined as the highest and most effective level ofdisinfection, HLD destroys mycobacteria (i.e., is tuberculocidal), viruses,fungal spores and vegetative bacteria.1 HLD also destroys some, but not all,bacterial endospores. It is the limited sporicidal activity of HLD thatdistinguishes it from sterilization (which destroys all microorganisms,including high numbers of bacterial endospores) and the other two levels ofdisinfection (neither of which is sporicidal) (see Tables 2 and 3). Mostimportantly, HLD destroys all pathogenic microorganisms encountered in theendoscopic setting, including Clostridium difficile,a spore-forming bacterium. (Almost all spore-forming bacteria arenon-pathogenic. Those few that do produce disease such as Bacillusanthracis and some species of the Clostridium genuseitherare destroyed by HLD or have not been associated with infection followingendoscopy.5
It is for this reason that differences in the infection ratesof rigid and flexible endoscopes subjected to sterilization or HLD have not beendocumented.5 Liquid chemical sterilants (LCSs) are frequently used to achieveHLD of endoscopes (see Table 2). LCSs that achieve HLD during short immersiontimes typically are sporicidal and destroy high numbers of bacterial endosporesduring long exposure times. One level below HLD is a less effective process known as ILD(see Table 2).1 Whereas processes that achieve sterilization and HLD areregulated by the Food and Drug Administration (FDA), ILDs (and LLDs) areregulated instead by the Environmental Protection Agency (EPA). In general, ILDdestroys lipid or medium-sized viruses, most non-lipid or small viruses, fungalspores, and vegetative bacteria. Like HLD, ILD is tuberculocidal. But whatdifferentiates ILD from HLD (and sterilization) is its inability to destroybacterial endospores, even during long exposure times. Examples of ILDs includeiodophor and phenolic compounds. Concentrated quaternary ammoniumcleaner/disinfectants may also be classified as ILDs. The third and lowest levelof disinfection, LLD, destroys fungal spores, vegetative bacteria, and lipid ormedium-sized viruses.1 But unlike ILD, LLD is not tuberculocidal (see Tables 2and 3). Examples include diluted quaternary ammonium cleaner/disinfectants.
Selection of a Sterilization, Disinfection Process
For many reasons, selection of an appropriate sterilization ordisinfection process or technology for reprocessing a specific reusable medicalinstrument (or environmental surface in the healthcare setting) is not alwaysstraightforward. If every reusable medical instrument were constructed ofstainless steel and other durable materials not damaged by heat, pressure andmoisture, few reprocessing dilemmas would arise, and the simple and obvious, ifonly, choice for reprocessing instruments would be steam sterilization. Indeed,steam sterilization is the method of choice, because it is effective, fast acting, andinexpensive.6
But the demand to improve patient morbidity, minimize theinvasiveness of surgery, and reduce healthcare costs, coupled with significantadvances in fiber-optic technology and materials engineering, spurned thedevelopment of delicate instruments many of which are heat-sensitive andarguably designed more to simplify complicated medical procedures than tofacilitate reprocessing. For these heat-sensitive instruments, several differenttypes of low-temperature sterilization and disinfection processes weredeveloped.
In addition to raising questions of materials compatibility,however, some low-temperature sterilization processes may be less effective and considerably more expensive per cycle than steamsterilization.6 Moreover, complicating selection of an appropriatereprocessing process for a specific heat-sensitive reusable instrument, somelow-temperature sterilization processes have limited applications and arecontraindicated for reprocessing instruments with long and narrow internalchannels, such as flexible gastrointestinal endoscopes. Also, not every reusableinstrument requires sterilization. In many instances, disinfection is adequateto prevent patient-to-patient disease transmission.
Although at times challenging, selection of an appropriatereprocessing technology for a specific instrument can be simplified bydovetailing the three-tiered classification scheme for medical instrumentsdisplayed in Table 1 with the definitions and relative effectiveness ofsterilization and disinfection (see Tables 2 and 3). In general, criticalinstruments, such as reusable biopsy forceps, require steam sterilization (Table2).1,7,8 For heatsensitive critical instruments, such as some models ofarthroscopes and laparoscopes, a low-temperature sterilization process may beindicated.1 (Refer to the sterilizers labeling and the instrumentsreprocessing instructions regarding recommended processes, effectiveness andcompatibility.) Alternatively, if sterilization is not feasible, HLD is recommended.1
HLD is also recommended for semi-critical instruments(although a low-temperature sterilization process may also be acceptable, aswell as steam sterilization if the instrument is not damaged by heat).1,7,8Published guidelines emphasize that subjecting an arthroscope, laparoscope(critical instruments) or a flexible endoscope (a semi-critical instrument) toHLD instead of sterilization is acceptable and does not pose an infectionrisk.1,5,7,8 In accordance with published guidelines, their classification assemi-critical instruments (see Table 1), and their manufacturers reprocessinginstructions, HLD is recommended for rhino-laryngoscopes,naso-pharyngo-laryngoscopes, and the blades and handles of rigid laryngoscopes (see Table 1).1-12
Finally, products that achieve ILD and LLD specifically,general purpose cleaner/disinfectants approved for use in medical facilities(see Table 2) are recommended for and limited to cleaning and disinfectingnon-critical instruments and environmental surfaces.1 (With very few exceptions,ILD may be acceptable for a limited number of semi-critical devices, such ashydrotherapy tanks, but not endoscopes. Refer to the specific instrumentsreprocessing instructions.)
Quaternary Ammonium Products
Quaternary ammonium products (or compounds) arebroad-spectrum, EPA-registered, cleaner/disinfectants. Depending on theirconcentrations, quaternary ammonium products intended for use in medicalfacilities are labeled for ILD or LLD and therefore may be used to clean,deodorize and disinfect non-critical items and hard, non-porous environmentalsurfaces. In accordance with their labeling, quaternary ammoniumproducts may also be used to pre-clean critical and semi-critical medicalinstruments prior to HLD or (sterilization). (Refer to the instrumentsreprocessing instructions to ensure materials compatibility with quaternaryammonium cleaner/disinfectants.)
Quaternary ammonium cleaner/disinfectants used in medicalfacilities are labeled for ILD or LLD not HLD and therefore, whileindicated for cleaning and disinfecting non-critical items and environmentalsurfaces, are contraindicated for flexible endoscopes. In particular, use of aquaternary ammonium disinfectant to clean and disinfect rhino-laryngoscopes,nasopharyngo- laryngoscopes, other types of flexible laryngoscopes, and theblades and handles of rigid laryngoscopes is not an accepted practice,potentially unsafe, and a violation of the standard of care. Cleaning using anappropriate detergent (e.g., enzymatic detergent) followed by HLD at a minimumis required for these semi-critical instruments as part of a complete andvalidated reprocessing protocol.1-4,10-12 Use of quaternary ammonium products toclean and disinfect surgical instruments has been linked to disease transmission.9
Further, although the handles of rigid laryngoscopes may notalways directly contact the patient, reports have demonstrated theircontamination with opportunistic pathogens.10 Published guidelines recommendthat these handles (and blades) be cleaned and subjected to HLD (orsterilization)1-4,10,12. Steam sterilization of the laryngoscopes handle andblade may also be acceptable, although flash sterilization may becontraindicated. Review the laryngoscopes reprocessing instructions for alist of compatible processes.
Lawrence F Muscarella, PhD, is the director of research anddevelopment and chief, infection control for Custom Ultrasonics, Inc. He is also editor of The Q-Net Monthly(www.myendosite.com). He can be reached via email at email@example.com.
Table 1: Classification Scheme for Medical Instruments
Penetrate sterile tissue, enter the vasculature, orcontact the patients blood.
Examples: Cardiac catheters, biopsyforceps and implants.
Contact mucous membranes or non-intact skin.
Examples: Rhino-laryngoscopes,naso-pharyngo-laryngoscopes, and the blades and handles of rigid laryngoscopes.1-4
Do not directly contact the patient, or only contact thepatients intact skin.
Examples: Blood pressure cuffs,stethoscopes and bedpans; and environmental surfaces, such as walls, floors andsink tops.
Table 2: The Definitions, Characteristics and RelativeEffectiveness of Sterilization and Disinfection
(Sterilization or the level of disinfection appropriate forcritical, semicritical and non-critical medical instruments is listed)
Sterilization Destroys all microorganisms, including bacterialendospores.
Sporicidal, tuberculocidal, virucidal, fungicidal andbactericidal.
Uses bacterial endospores as biological indicators.
Examples: Pressurized steam,ethylene oxide gas, hydrogen peroxide plasma.
Primarily used for critical instruments.
High-level disinfection (HLD)
Destroys all pathogenic microorganisms, including some bacterial endosporesduring short exposure times.
Typically destroys high numbers of bacterial endosporesduring long exposures times.
Sporicidal (limited), tuberculocidal, virucidal,fungicidal and bactericidal.
Uses mycobacteria as indicators of effectiveness.
Examples: 2 percent glutaraldehyde,7.5 percent hydrogen peroxide, 0.2 percent peracetic acid.
Primarily used for semicritical instruments.
Intermediate-level disinfection (ILD)
Destroys many types of microorganisms including mycobacteria.
Tuberculocidal, virucidal, fungicidal and bactericidal.
May use mycobacteria, viruses as indicators ofeffectiveness.
Examples: 70 percent isopropylalcohol, iodophor and phenolic compounds, concentrated quaternary ammoniumcompounds (e.g., hospital cleaner/disinfectants with a tuberculocidal claim). Primarily used for non-critical instruments.
Low-level disinfection (LLD)
Destroys some types of microorganisms.
Neither sporicidal nor tuberculocidal.
Virucidal (limited), fungicidal and bactericidal.
May use the hepatitis B virus, HIV as indicators ofeffectiveness.
Examples: Diluted quaternaryammonium compounds (e.g., hospital cleaner/disinfectants without atuberculocidal claim).
Primarily used for non-critical instruments.
Table 3: The Relative Resistance of Different Types ofMicroorganisms to Sterilization and Disinfection
(Listed in decreasing order of resistance of microorganisms tosterilization and disinfection. In general, bacterial endospores and prions arethe hardest to destroy and lipid viruses are the easiest to destroy.)
Prions May require extended, multiple sterilizationcycles.
May be responsible for transmissible spongiformencephalopathies.
Bacterial endospores Destroyedby sterilization.
Some bacterial endospores can also be destroyed by HLD.*
Example: Bacillus stearothermophilus
Mycobacteria Destroyed by sterilization, HLD and ILD.
Example: Mycobacterium tuberculosis
Non-lipidor small viruses
Destroyed by sterilization, HLDand ILD.
Example: the polio virus
Fungi(molds and yeasts)
Destroyed by sterilization, HLDand ILD.
Some fungi are also destroyed by LLD.
Example: Candida albicans
Destroyed by sterilization, HLD, ILD andLLD.
Example: Pseudomonas aeruginosa
Lipidor medium-sized viruses
Destroyed bysterilization, HLD, ILD and LLD.
Example: the hepatitis B virus, HIV*HLD = High-level disinfection; ILD = Intermediate-level disinfection; LLD = Low-level disinfection
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