Bennett & Brachman's Hospital Infections, 5th Edition

20

Sterilization and Disinfection

William A. Rutala

David J. Weber

Introduction

In the United States in 1996, there were approximately 46,500,000 surgical procedures and an even larger number of invasive medical procedures [1]. For example, there are about 5 million gastrointestinal endoscopies per year [1]. Each of these procedures involves contact by a medical device or surgical instrument with a patient's sterile tissue or mucous membranes. A major risk of all such procedures is the introduction of pathogenic microbes that can lead to infection. For example, failure to properly disinfect or sterilize equipment has led to person-to-person transmission via contaminated devices (e.g., M. tuberculosis–contaminated bronchoscopes).

Achieving disinfection and sterilization through the use of disinfectants and sterilization practices is essential for ensuring that medical and surgical instruments do not transmit infectious pathogens to patients. Because it is not necessary to sterilize all patient-care items, healthcare policies must identify whether cleaning, disinfection, or sterilization is indicated based primarily on each item's intended use.

Multiple studies in many countries have documented lack of compliance with established guidelines for disinfection and sterilization [2,3]. Failure to comply with scientifically based guidelines has led to numerous outbreaks [3,4,5,6,7]. In this chapter, which is an updated version of other publications [8,9,10,11,12], a pragmatic approach to the judicious selection and proper use of disinfection and sterilization processes is presented.

Definition of Terms

Sterilization describes a process that destroys or eliminates all forms of microbial life and is carried out in healthcare facilities by either physical or chemical methods. Steam under pressure, dry heat, ethylene oxide (ETO) gas, hydrogen peroxide gas plasma, and liquid chemicals are the principal sterilizing agents used in healthcare facilities. When chemicals are used for the purposes of destroying all forms of microbiological life, including bacterial spores, they may be called chemical sterilants. These same germicides used for shorter exposure periods also may be part of the disinfection process (i.e., high-level disinfection).

Disinfection describes a process that eliminates many or all pathogenic microorganisms on inanimate objects with the exception of bacterial spores. Disinfection usually is accomplished by the use of liquid chemicals or wet pasteurization in healthcare settings. The efficacy of disinfection is affected by a number of factors, each of which may nullify or limit the efficacy of the process. Some of the factors that affect both disinfection and sterilization efficacy are the prior cleaning of the object, the organic and inorganic load present, the type and level of microbial contamination, the concentration of and exposure time to the germicide, the design of the object (e.g., crevices, hinges, and narrow lumens), the presence of biofilms, the temperature and pH of the disinfection process, and, in some instances, the relative humidity of the sterilization process (e.g., ethylene oxide) [9,13].

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By definition, then, disinfection differs from sterilization by its lack of sporicidal property, but this is an oversimplification. A few disinfectants will kill spores with prolonged exposure times (3–12 hours) and are called chemical sterilants. At similar concentrations but with shorter exposure periods (e.g., 20 minutes for 2% glutaraldehyde), these same disinfectants, called high-level disinfectants, will kill all microorganisms with the exception of large numbers of bacterial spores. Low-level disinfectants will kill most vegetative bacteria, some fungi, and some viruses in a practical period of time (≤10 minutes), whereas intermediate-level disinfectants may be cidal for mycobacteria, vegetative bacteria, most viruses, and most fungi but do not necessarily kill bacterial spores. The germicides differ markedly among themselves primarily in their antimicrobial spectrum and rapidity of action. A number of products and processes can be used to disinfect or sterilize medical and surgical instruments based on the risk of infection involved in the use of the item (Table 20-1).

Terms with a suffix “cide” or “cidal” for killing action also are commonly used. For example, a germicide is an agent that can kill microorganisms, particularly pathogenic organisms (“germs”). The term germicide includes both antiseptics and disinfectants. Antiseptics are germicides applied to living tissue and skin while disinfectants are antimicrobials applied only to inanimate objects. In general, antiseptics are used only on the skin, not for surface disinfection, and disinfectants are not used for skin antisepsis because they may cause injury to skin and other tissues. Other words with the suffix “cide” (e.g., virucide, fungicide, bactericide, sporicide, and tuberculocide) can kill the type of microorganism identified by the prefix. For example, a bactericide is an agent that kills bacteria [8,11,14,15,16,17,18].

A Rational Approach to Disinfection and Sterilization

More than 35 years ago, Earle H. Spaulding [15] devised a rational approach to disinfection and sterilization of patient-care items or equipment. This classification scheme is so clear and logical that it has been retained, refined, and successfully used by infection control professionals and others when planning methods for disinfection or sterilization [8,13,14,16,19,20]. Spaulding believed that the nature of disinfection could be understood more readily if instruments and items for patient care were divided into three categories based on the degree of risk of infection involved in the use of the items. The three categories he described were critical, semicritical, and noncritical. This terminology is employed by the CDC's “Guidelines for Environmental Infection Control in Healthcare Facilities” [21] and the CDC's “Guideline for Disinfection and Sterilization in Healthcare Facilities” [13].

Critical Items

Critical items are so called because of the high risk of infection if such an item is contaminated with any microorganism, including bacterial spores. Thus, it is critical that objects that enter sterile tissue or the vascular system be sterile because any microbial contamination could result in pathogen transmission. This category includes surgical instruments, cardiac and urinary catheters, implants, and ultrasound probes used in sterile body cavities. The items in this category should be purchased as sterile or be sterilized by steam sterilization if possible. If heat sensitive, the object may be treated with ethylene oxide (ETO) or hydrogen peroxide gas plasma or by liquid chemical sterilants if other methods are unsuitable. Tables 20-2 and 20-3 list several germicides categorized as chemical sterilants. These include ≥ 2.40% glutaraldehyde-based formulations, 1.12% glutaraldehyde with 1.93% phenol/phenate, 7.50% stabilized hydrogen peroxide, 7.35% hydrogen peroxide with 0.23% peracetic acid, 0.20% peracetic acid, and 1.00% hydrogen peroxide with 0.08% peracetic acid. With the exception of 0.20% peracetic acid (12 minutes at 50°–56°C), the indicated exposure times range from 3 to 12 hours [22]. Liquid chemical sterilants can be relied on to produce sterility only if cleaning, which eliminates organic and inorganic material, precedes treatment and if proper guidelines on concentration, contact time, temperature, and pH are met. Another limitation to sterilization of devices with liquid chemical sterilants is that the devices cannot be wrapped during processing in a liquid chemical sterilant; thus, it is impossible to maintain sterility following processing and during storage. Furthermore, devices may require rinsing following exposure to the liquid chemical sterilant with water that generally is not sterile. Therefore, due to the inherent limitations of using liquid chemical sterilants in a nonautomated reprocessor, their use should be restricted to reprocessing critical devices that are heat sensitive and incompatible with other sterilization methods.

Semicritical Items

Semicritical items are those that come in contact with mucous membranes or nonintact skin. Respiratory therapy and anesthesia equipment, some endoscopes, laryngoscope blades, esophageal manometry probes, vaginal and rectal probes, anorectal manometry catheters, and diaphragm fitting rings are included in this category. These medical devices should be free of all microorganisms (i.e., mycobacteria, fungi, viruses, bacteria), although small numbers of bacterial spores may be present. Intact mucous membranes, such as those of the lungs or the gastrointestinal tract, generally are resistant to infection by common bacterial spores but susceptible to other organisms such as bacteria, mycobacteria, and viruses.

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Semicritical items minimally require high-level disinfection using chemical disinfectants. Glutaraldehyde, hydrogen peroxide, ortho-phthalaldehyde, peracetic acid with hydrogen peroxide, and chlorine are cleared by the Food and Drug Administration (FDA) [22] and are dependable high-level disinfectants provided the factors influencing germicidal procedures are met (Tables 20-2 and 20-3). The exposure time for most high-level disinfectants varies from 10–45 minutes at 20°–25°C. Outbreaks continue to occur when ineffective disinfectants, including iodophor, alcohol, and overdiluted glutaraldehyde [5], are used for “high-level disinfection.” When a disinfectant is selected for use with certain patient-care items, the chemical compatibility after extended use with the items to be disinfected also must be considered. For example, compatibility testing by Olympus America of the 7.5% hydrogen peroxide found cosmetic and functional changes with the tested endoscopes (Olympus America, written communication, October 15, 1999). Similarly, Olympus does not endorse the use of the hydrogen peroxide with peracetic acid products due to cosmetic and functional damage (Olympus America, written communication, April 15, 1998 and September 13, 2000).

TABLE 20-1 METHODS OF STERILIZATION AND DISINFECTION

Sterilization Disinfection Critical Items (Will Enter Tissue or Vascular System or Blood Will Flow Through Them) High Level (Semicritical Items; [Except Dental] Will Come in Contact with Mucous Membrane or Nonintact Skin) Intermediate-Level (Some Semicritical Itemsa and Noncritical Items) Low-Level (Noncritical Items; Will Come in Contact with Intact Skin) Object Procedure Exposure Time Procedure (Exposure Time 12–30 min at ≥20°C) Procedure (Exposure Time ≥1 m) Procedure (Exposure Time ≥1 m) Modified from Rutala (8,18,127) and Simmons (16). The selection and use of disinfectants in the healthcare field is dynamic, and products may become available that did not exist when this guideline was written. As newer disinfectants become available, persons or committees responsible for selecting disinfectants and sterilization processes should be guided by products cleared by the FDA and the EPA as well as information in the scientific literature. A. Heat sterilization, including steam or hot air (see manufacturer's recommendations; steam sterilization processing time from 3–30 minutes). B. Ethylene oxide gas (see manufacturer's recommendations, generally 1–6 hours processing time plus aeration time of 8–12 hours at 50–60° C). C. Hydrogen peroxide gas plasma (see manufacturer's recommendations for internal diameter and length restrictions, processing time between 45–72 minutes) D. Glutaraldehyde-based formulations (≥2% glutaraldehyde; caution should be exercised with all glutaraldehyde formulations when further in-use dilution is anticipated), glutaraldehyde (1.12%), and 1.93% phenol/phenate. One glutaraldehyde-based product has a high-level disinfection claim of 5 minutes at 35°C. E. Ortho-phthalaldehyde (OPA) 0.55%. F. Hydrogen peroxide 7.5% (will corrode copper, zinc, and brass). G. Peracetic acid, concentration variable but 0.2% or greater is sporicidal. Peracetic acid immersion system operates at 50–56°C. H. Hydrogen peroxide (7.35%) and 0.23% peracetic acid; hydrogen peroxide 1% and 0.08% peracetic acid (will corrode metal instruments). I. Wet pasteurization at 70°C for 30 minutes with detergent cleaning. J. Hypochlorite, single-use chlorine generated on-site by electrolyzing saline containing >650–675 active free chlorine (will corrode metal instruments). K. Ethyl or isopropyl alcohol (70–90%). L. Sodium hypochlorite (5.25–6.15% household bleach diluted 1:500 provides >100ppm available chlorine). M. Phenolic germicidal detergent solution (follow product label for use-dilution). N. Iodophor germicidal detergent solution (follow product label for use-dilution). O. Quaternary ammonium germicidal detergent solution (follow product label for use-dilution). MR. Manufacturer's recommendations. NA. Not applicable. a Some items that may come in contact with nonintact skin for a brief period of time (e.g., hydrotherapy tanks) are usually considered noncritical surfaces and are disinfected with intermediate-level disinfectants (i.e., phenolic, iodophor, alcohol, chlorine). b The longer the exposure to a disinfectant, the more likely it is that all microorganisms will be eliminated. Ten-minute exposure is not adequate to disinfect many objects, especially those that are difficult to clean because they have narrow channels or other areas that can harbor organic material and bacteria. Twenty-minute exposure at 20°C is the minimum time needed to reliably kill M. tuberculosis and nontuberculous mycobacteria with a 2% glutaraldehyde. With the exception of >2% glutaraldehydes, follow the FDA-cleared high-level disinfection claim. Some high-level disinfectants have a reduced exposure time (e.g., ortho-phthalaldehyde at 12 minutes at 20°C) because of their rapid activity against mycobacteria or reduced exposure time due to increased mycobactericidal activity at elevated temperature (e.g., 2.5% glutaraldehyde at 5 minutes at 35°C, 0.55% OPA at 5min at 25°C in automated endoscope reprocessor). c Tubing must be completely filled for high-level disinfection and liquid chemical sterilization; care must be taken to avoid entrapment of air bubbles during immersion. d Material compatibility should be investigated when appropriate. e A concentration of 1000ppm available chlorine should be considered where cultures or concentrated preparations of microorganisms have spilled (5.25% to 6.15% household bleach diluted 1:50 provides >1000ppm available chlorine). This solution may corrode some surfaces. f Pasteurization (washer-disinfector) of respiratory therapy or anesthesia equipment is a recognized alternative to high-level disinfection. Some data challenge the efficacy of some pasteurization units. g Thermostability should be investigated when appropriate. h Do not mix rectal and oral thermometers at any stage of handling or processing. Smooth, hard A MR D K K Surfacea,d B MR E Le L C MR F M M D 10 h at 20–25°C H N N F 6 h If O G 12 m at 50–56°C J H 3–8 h Rubber tubing and cathetersc,d A MR D B MR E C MR F D 10 h at 20–25°C H F 6 h If G 12 m at 50–56°C J H 3–8 h Polyethylene tubing and cathetersc,d,g A MR D B MR E C MR F D 10 h at 20–25°C H F 6 h If G 12 m at 50–56°C J H 3–8 h Lensed instrumentsd A MR D B MR E C MR F D 10 h at 20–25°C H F 6 h J G 12 m at 50–56°C H 3–8 h Thermometers (oral and rectal)h Kh Hinged instrumentsd A MR D B MR E C MR F

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Semicritical items that will have contact with the mucous membranes of the respiratory tract or gastrointestinal tract should be rinsed with sterile water, filtered water, or tap water followed by an alcohol rinse [13,23,24]. An alcohol rinse and forced-air drying markedly reduces the likelihood of contamination of the instrument (e.g., endoscope), most likely by removing the wet environment favorable for bacterial growth [24]. After rinsing, items should be dried and stored in a manner that protects them from damage or contamination. There is no recommendation to use sterile or filtered water rather than tap water for rinsing semicritical equipment that will have contact with the mucous membranes of the rectum (e.g., rectal probes, anoscope) or vagina (e.g., vaginal probes) [13].

TABLE 20-2 COMPARISON OF THE CHARACTERISTICS OF SELECTED CHEMICALS USED AS HIGH-LEVEL DISINFECTANTS OR CHEMICAL STERILANTS

HP (7.5%) PA (0.2%) Glut (≥2.0%) OPA (0.55%) HP/PA (7.35%/0.23%) Modified from Rutala, Weber (128). Abbreviations: AER, automated endoscope reprocessor; HLD, high-level disinfectant; HP, hydrogen peroxide; PA, peracetic acid; Glut, glutaraldehyde; PA/HP, peracetic acid and hydrogen peroxide; OPA, ortho-phthalaldehyde (FDA cleared as a high-level disinfectant, included for comparison to other chemical agents used for high-level disinfection); m, minutes; h, hours; NA, not applicable; TWA, time-weighted average for a conventional 8-hour workday. a Number of days a product can be reused as determined by reuse protocol. b Time a product can remain in storage (unused). c No U.S. EPA regulations but some states and local authorities have additional restrictions. d MEC = minimum effective concentration is the lowest concentration of active ingredients at which the product is still effective. e Conc soln = concentrated solution. f The ceiling limit recommended by the American Conference of Governmental Industrial Hygienists is 0.05 ppm. g Per cycle cost profile considers cost of the processing solution and assumes maximum use life (e.g., 21 days for hydrogen peroxide, 14 days for glutaraldehyde), 5 reprocessing cycles per day, 1-gallon basin for manual processing, and 4-gallon tank for automated processing.+ = least expensive; +++++ = most expensive. HLD claim 30 m @ 20°C NA 20–90 m @ 20°–25°C 12 m @ 20°C, 5 m @ 25°C in AER 15 m @ 20°C Sterilization claim 6 h @ 20° 12m @ 50°–56°C 10 h @ 20°–25°C None 3 h @ 20°C Activation No No Yes (alkaline glut) No No Reuse lifea 21d Single use 14–30 d 14d 14d Shelf life stabilityb 2 y 6 mo 2 y 2 y 2 y Disposal restrictions None None Localc Localc None Materials compatibility Good Good Excellent Excellent No data Monitor MECd Yes (6%) No Yes (1.5% or higher) Yes (0.3% OPA) No Safety Serious eye damage (safety glasses) Serious eye and skin damage (conc soln)e Respiratory Eye irritant, stains skin Eye damage Processing Manual or automated Automated Manual or automated Manual or automated Manual Organic material resistance Yes Yes Yes Yes Yes OSHA exposure limit 1 ppm TWA None Nonef None HP-1 ppm TWA Cost profile (per cycle)g + (manual), + + (automated) + + + + + (automated) + (manual), + + (automated) + + (manual) + + (manual)

Noncritical Items

Noncritical items are those that come in contact with intact skin but not mucous membranes. Intact skin acts as an effective barrier to most microorganisms; therefore, the sterility of items coming in contact with intact skin is “not critical.” Examples of noncritical items are bedpans, blood pressure cuffs, crutches, bed rails, computers, linens, bedside tables, patient furniture, and floors. In contrast to critical and some semicritical items, most noncritical reusable items may be decontaminated where they are used and do not need to be transported to a central processing area. There is virtually no documented risk of transmitting infectious agents to patients via noncritical items [25] when they are used as noncritical items and do

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not contact non-intact skin and/or mucous membranes. However, these items (e.g., bedside tables, bed rails) could potentially contribute to secondary transmission by contaminating hands of healthcare workers or by contact with medical equipment that will subsequently come in contact with patients [26]. Table 20-1 lists several low-level disinfectants that may be used for noncritical items. The exposure time listed in the table is at least 1 minute.

TABLE 20-3 SUMMARY OF ADVANTAGES AND DISADVANTAGES OF CHEMICAL AGENTS USED AS CHEMICAL STERILANTSa OR AS HIGH-LEVEL DISINFECTANTS

Sterilization Method Advantages Disadvantages Modified from (128). aAll products effective in presence of organic soil, relatively easy to use, and have a broad spectrum of antimicrobial activity (bacteria, fungi, viruses, bacterial spores, and mycobacteria). These characteristics are documented in the literature; contact the manufacturer of the instrument and sterilant for additional information. All products listed are FDA-cleared as chemical sterilants except OPA, which is an FDA-cleared, high-level disinfectant. Peracetic acid/hydrogen peroxide · No activation required · Odor or irritation not significant · Material compatibility concerns (lead, brass, copper, zinc) both cosmetic and functional · Limited clinical experience · Potential for eye and skin damage Glutaraldehyde · Numerous use studies published · Relatively inexpensive · Excellent material compatibility · Respiratory irritation from glutaraldehyde vapor · Pungent and irritating odor · Relatively slow mycobactericidal activity · Coagulates blood and fixes tissue to surfaces · Allergic contact dermatitis Hydrogen peroxide · No activation required · May enhance removal of organic matter and organisms · No disposal issues · No odor or irritation issues · Does not coagulate blood or fix tissues to surfaces · Inactivates Cryptosporidium · Use studies published · Material compatibility concerns (brass, zinc, copper, and nickel/silver plating) both cosmetic and functional · Serious eye damage with contact Ortho-phthalaldehyde · Fast-acting, high-level disinfectant · No activation required · Odor not significant · Excellent materials compatibility claimed · Does not coagulate blood or fix tissues to surfaces claimed · Stains protein gray (e.g., skin, mucous membranes, clothing, and environmental surfaces) · More expensive than glutaraldehyde · Eye irritation with contact · Slow sporicidal activity · Exposure may result in hypersensitivity Peracetic acid · Rapid sterilization cycle time (30–45 minutes) · Low temperature (50°–55°C) liquid immersion sterilization · Environmental friendly by-products (acetic acid, O2, H20) · Fully automated · Single-use system eliminates need for concentration testing · Standardized cycle · May enhance removal of organic material and endotoxin · No adverse health effects to operators under normal operating conditions · Compatible with many materials and instruments · Does not coagulate blood or fix tissues to surfaces · Sterilant flows through scope facilitating salt, protein, and microbe removal · Rapidly sporicidal · Provides procedure standardization (constant dilution, perfusion of channel, temperatures, exposure) · Potential material incompatibility (e.g., aluminum anodized coating becomes dull) · Used for immersible instruments only · Biological indicator may not be suitable for routine monitoring · One scope or a small number of instruments can be processed in a cycle · More expensive (endoscope repairs, operating costs, purchase costs) than high-level disinfection · Serious eye and skin damage (concentrated solution) with contact · Point-of-use system, no sterile storage

An Overview of Cleaning, Disinfection, and Sterilization

Cleaning

Cleaning is the removal of foreign material (e.g., soil and organic material) from objects, and it is normally accomplished using water with detergents or enzymatic products. Thorough cleaning is required before high-level disinfection and sterilization because inorganic and organic materials that remain on the surfaces of instruments interfere with the effectiveness of these processes. Also, if the soiled materials become dried or baked onto the instruments, the removal process becomes more difficult and the disinfection or sterilization process less effective or ineffective. Surgical instruments should be presoaked or rinsed to prevent drying of blood and to soften or remove blood from the instruments.

Cleaning is done manually when the use area does not have a mechanical unit (e.g., ultrasonic cleaner or washer-disinfector) and for fragile or difficult-to-clean instruments. If cleaning is done manually, the two essential components are friction and fluidics. Using friction (e.g., rubbing/scrubbing the soiled area with a brush) is an old and dependable method. Fluidics (i.e., fluids under pressure) is used to remove soil and debris from internal channels after brushing and when the design does not allow the passage of a brush through a channel [27]. When using a washer-disinfector, care should be taken as to the method of loading instruments. Hinged instruments should be opened fully to allow adequate contact with the detergent solution. The stacking of instruments in washers should be avoided. Instruments should be disassembled as much as possible.

Disinfection

A great number of disinfectants are used alone or in combinations (e.g., hydrogen peroxide and peracetic acid) in the healthcare setting. These include alcohols, chlorine and chlorine compounds, formaldehyde, glutaraldehyde, ortho-phthalaldehyde, hydrogen peroxide, iodophors, peracetic acid, phenolics, and quaternary ammonium compounds. Commercial formulations based on these chemicals are considered unique products and must be registered with the Environmental Protection Agency (EPA) or cleared by the FDA. In most instances, a given product is designed for a specific purpose and is to be used in a certain manner. Therefore, the label should be read carefully to ensure that the right product is selected for the intended use and applied in an appropriate manner.

Disinfectants are not interchangeable, so the user must have sufficient information to select an appropriate disinfectant for any item and use it in the most efficient way. An overview of germicides commonly used in healthcare can be found in other references [9,11,13]. It should be recognized that excessive costs may be attributed to incorrect concentrations and inappropriate disinfectants. Finally, occupational diseases among cleaning personnel have been associated with the use of several disinfectants such as formaldehyde, glutaraldehyde, chlorine, and others, and precautions (e.g., gloves, proper ventilation) should be used to minimize exposure [28,29,30].

Sterilization

Most medical and surgical devices used in healthcare facilities are made of materials that are heat stable and thus can be sterilized by heat, primarily steam sterilization. However, since 1950, there has been an increase in medical devices and instruments made of materials (e.g., plastics) that require low-temperature sterilization. Ethylene oxide gas has been used since the 1950s for heat- and moisture-sensitive medical devices. Within the past 20 years, a number of new, low-temperature sterilization systems (e.g., hydrogen peroxide gas plasma, peracetic acid immersion) have been developed and are being used to sterilize medical devices. Table 20-4 reviews sterilization technologies used in healthcare and makes recommendations for their optimum performance in the processing of medical devices [18,19,31,32,33,34,35,36,37,38].

Sterilization destroys all microorganisms on the surface of an item or in a fluid to prevent disease transmission associated with the use of that item. While the use of inadequately sterilized critical items represents a high risk of transmitting pathogens, documented transmission of pathogens associated with an inadequately sterilized critical item is exceedingly rare [39,40]. This is likely due to the wide margin of safety associated with the sterilization processes used in healthcare facilities. The concept of what constitutes “sterile” is measured as a probability of sterility for each item to be sterilized. This probability is commonly referred to as the sterility assurance level (SAL) of the product and is defined as the probability of a single viable microorganism occurring on a product after sterilization. SAL is normally expressed as 10^-n. For example, if the probability of a spore surviving were 1 in 1 million, the SAL would be 10^-6 [41,42]. In short, an SAL is an estimate of lethality of the entire sterilization process and is a conservative calculation. Dual SALs (e.g., 10^-3 SAL for blood culture tubes, drainage bags; 10^-6 SAL for scalpels, implants) have been used in the United States for many

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years; the choice of a 10^-6 SAL was strictly arbitrary and not associated with any adverse outcomes (e.g., patient infections) [41].

TABLE 20-4 SUMMARY OF ADVANTAGES AND DISADVANTAGES OF COMMONLY USED STERILIZATION TECHNOLOGIES

Sterilization Method Advantages Disadvantages Modified from (129). Abbreviations: ETO, ethylene oxide; CFC, chlorofluorocarbon; HCFC, hydrochlorofluorocarbon. Steam · Nontoxic to patient, staff, environment · Cycle easy to control and monitor · Rapidly microbicidal · Least affected by organic/inorganic soils among sterilization processes listed · Rapid cycle time · Penetrates medical packing, device lumens · Deleterious for heat-sensitive instruments · Microsurgical instruments damaged by repeated exposure · May leave instruments wet, causing them to rust · Potential for burns (flash sterilization) Hydrogen peroxide gas plasma · Safe for the environment · Leaves no toxic residuals · Cycle time is 28–75 minutes (varies with model type) and no aeration necessary · Used for heat- and moisture-sensitive items since process temperature <50°C · Simple to operate, install (208 V outlet), and monitor · Compatible with most medical devices · Requires only electrical outlet · Cellulose (paper), linens, and liquids cannot be processed · Sterilization chamber size from 1.8–9.5 ft3 total volume (varies with model type) · Endoscope or medical device restrictions based on lumen internal diameter and length (see manufacturer's recommendations) · Requires synthetic packaging (polypropylene wraps, polyolefin pouches) and special container tray · Hydrogen peroxide may be toxic at levels greater than 1 ppm TWA 100% ethylene oxide (ETO) · Penetrates packaging materials, device lumens · Single-dose cartridge and negative-pressure chamber minimizes the potential for gas leak and ETO exposure · Simple to operate and monitor · Compatible with most medical materials · Requires aeration time to remove ETO residue · Sterilization chamber size from 4 ft3 to 7.9 ft3 total volume (varies with model type) · ETO is toxic, a carcinogen, and flammable · ETO emission regulated by states but catalytic cell removes 99.9% of ETO and converts it to CO2 and H2O · ETO cartridges should be stored in flammable liquid storage cabinet · Lengthy cycle/aeration time ETO Mixtures 8.6% ETO/91.4% HCFC 10.0% ETO/90.0% HCFC 8.5% ETO/91.5% CO2 · Penetrates medical packaging and many plastics · Compatible with most medical materials · Cycle easy to control and monitor · Some states require ETO emission reduction of 90–99.9% · CFC (inert gas that eliminates explosion hazard) banned in 1995 · Potential hazards to staff and patients · Lengthy cycle/aeration time · ETO is toxic, a carcinogen, and flammable Peracetic acid · Rapid cycle time (30–45 minutes) Low temperature (50°–55°C) liquid immersion sterilization · Environmentally friendly by-products · Sterilant flows through endoscope which facilitates salt, protein, and microbe removal · Point-of-use system, no sterile storage · Biological indicator may not be suitable for routine monitoring · Used for immersible instruments only · Some material incompatibility (e.g., aluminum anodized coating becomes dull) · One scope or a small number of instruments processed in a cycle · Potential for serious eye and skin damage (concentrated solution) with contact · Must use connector between system and scope to ensure infusion of sterilant to all channels

Current Issues in Disinfection and Sterilization

Reprocessing of Endoscopes

Physicians use endoscopes to diagnose and treat numerous medical disorders. While endoscopes represent a valuable diagnostic and therapeutic tool in modern medicine and the incidence of infection associated with their use has been reported as very low (about 1 in 1.8 million procedures) [43], more healthcare-associated outbreaks have been linked to contaminated endoscopes than to any other medical device [3,4,5]. To prevent the spread of healthcare-associated infections (HAIs), all heat-sensitive endoscopes (e.g., gastrointestinal endoscopes, bronchoscopes, nasopharyngoscopes) must be properly cleaned and at a minimum subjected to high-level disinfection following each use. High-level disinfection can be expected to destroy all microorganisms; although when high numbers of bacterial spores are present, a few spores may survive.

Recommendations for the cleaning and disinfection of endoscopic equipment have been published and should be strictly followed [13,23]. Unfortunately, audits have shown that personnel do not adhere to guidelines on reprocessing [44,45,46] and outbreaks of infection continue to occur [47,48]. To ensure that reprocessing personnel are properly trained, there should be initial and annual competency testing for each individual who is involved in reprocessing endoscopic instruments [13,23,24,49].

In general, endoscope disinfection or sterilization with a liquid chemical sterilant or high-level disinfectant involves five steps after leak testing: (1) clean—mechanically clean internal and external surfaces, including brushing internal channels and flushing each internal channel with water and an enzymatic cleaner; (2) disinfect—immerse endoscope in high-level disinfectant (or chemical sterilant) and perfuse disinfectant (eliminates air pockets and ensures contact of the germicide with the internal channels) into all accessible channels such as the suction/biopsy channel and air/water channel and expose for a time recommended for the specific high-level disinfectant; (3) rinse—rinse the endoscope and all channels with sterile water, filtered water (commonly used with automated endoscope reprocessors), or tap water; (4) dry—rinse the insertion tube and inner channels with alcohol and dry with forced air after disinfection and before storage; and (5) store—store the endoscope in a way that prevents recontamination and promotes drying (e.g., hung vertically).

Unfortunately, there is poor compliance with the recommendations for reprocessing endoscopes. In addition, there are rare instances when the scientific literature and recommendations from professional organizations regarding the use of disinfectants and sterliants may differ from the manufacturer's label claim. One example is the contact time used to achieve high-level disinfection with 2% glutaraldehyde. Based on FDA requirements (FDA regulates liquid sterilants and high-level disinfectants used on critical and semicritical medical devices), manufacturers test the efficacy of their germicide formulations under worst-case conditions (i.e., minimum recommended concentration of the active ingredient) and in the presence of organic soil (typically 5% serum). The soil is used to represent the organic loading to which the device is exposed during actual use and that would remain on the device in the absence of cleaning. These stringent test conditions are designed to provide a margin of safety by ensuring that the contact conditions for the germicide provide complete elimination of the test bacteria (e.g., 10⁵ to 10⁶ M. tuberculosis in organic soil and dried on a scope) if inoculated into the most difficult areas for the disinfectant to penetrate and in the absence of cleaning. However, the scientific data demonstrate that M. tuberculosis levels can be reduced by at least 8 log₁₀ with cleaning (4 log₁₀) followed by chemical disinfection for 20 minutes at 20°C (4 to 6 log₁₀) [13,22,23,50]. Because of these data, professional organizations (at least 14 professional organizations worldwide) that have endorsed an endoscope reprocessing guideline recommend contact conditions of 20 minutes at 20°C (or less than 20 minutes outside the United States) with 2% glutaraldehyde to achieve high-level disinfection that differs from that of the manufacturer's label [23,51,52,53,54].

It is important to emphasize that the FDA tests do not include cleaning, a critical component of the disinfection process. Therefore, when cleaning has been included in the test methodology, 2% glutaraldehyde for 20 minutes has been demonstrated to be effective in eliminating all vegetative bacteria [13,50].

Disinfection of HBV-, HCV-, HIV-, or M. tuberculosis–Contaminated Devices

The CDC recommendation for high-level disinfection of HBV-, HCV-, HIV-, or M. tuberculosis–contaminated devices is appropriate because experiments have demonstrated the effectiveness of high-level disinfectants to inactivate these and other pathogens that may contaminate semicritical devices [55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79]. Nonetheless, some healthcare facilities have modified their disinfection procedures when endoscopes are used with a patient known or suspected to be infected with HBV, HIV, or M. tuberculosis [80,81]. This is inconsistent with the concept of Universal Precautions that presumes that all patients are potentially infected with bloodborne pathogens [65]. Several studies have highlighted the inability to distinguish HBV- or HIV-infected patients from noninfected patients on clinical grounds [82,83,84]. It also is likely that mycobacterial

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infection will not be clinically apparent in many patients. In most instances, hospitals that altered their disinfection procedure used ethylene oxide sterilization on the endoscopic instruments because they believed this practice reduced the risk of infection [80,81]. ETO is not routinely used for endoscope sterilization because of the lengthy processing time. Endoscopes and other semicritical devices should be managed the same way whether or not the patient is known to be infected with HBV, HCV, HIV, or M. tuberculosis.

An evaluation of a manual disinfection procedure to eliminate HCV from experimentally contaminated endoscopes provided some evidence that cleaning and 2% glutaraldehyde for 20 minutes should prevent transmission [77]. Using experimentally contaminated hysteroscopes, Sartor et al. detected HCV by polymerase chain reaction (PCR) in one (3%) of 34 samples following cleaning with a detergent, but no samples were positive following treatment with a 2% glutaraldehyde solution for 20 minutes [85]. Rey et al. demonstrated complete elimination of HCV (as detected by PCR) from endoscopes used on chronically infected patients following cleaning and disinfection for 3 to 5 minutes in glutaraldehyde [86]. Similarly, Chanzy et al. used PCR to demonstrate complete elimination of HCV following standard disinfection of experimentally contaminated endoscopes [77] while Ishino et al. found that endoscopes used on patients who were positive for HCV antibody had no detectable HCV RNA after high-level disinfection [87]. The inhibitory activity of a phenolic and a chlorine compound on HCV showed that the phenolic inhibited the binding and replication of HCV but the chlorine was ineffective, probably due to its low concentration and its neutralization in the presence of organic matter [88].

Occupational Safety and Health Administration Bloodborne Pathogen Standard

In December 1991, the Occupational Safety and Health Administration (OSHA) promulgated the standard “Occupational Exposure to Bloodborne Pathogens” to eliminate or minimize occupational exposure to bloodborne pathogens [89]. One component of this requirement is that all equipment and environmental and working surfaces be cleaned and decontaminated with an appropriate disinfectant after contact with blood or other potentially infectious materials. While the OSHA standard does not specify the type of disinfectant or procedure, the OSHA original compliance document [90] suggested that a germicide must be tuberculocidal to kill the HBV. To follow the OSHA compliance document, a tuberculocidal disinfectant (e.g., phenolic and chlorine) would be needed to clean a blood spill. However, in February 1997, OSHA amended its policy and stated that EPA-registered disinfectants that are labeled as effective against HIV and HBV would be considered as appropriate disinfectants “provided such surfaces have not become contaminated with agent(s) or volumes of or concentrations of agent(s) for which higher level disinfection is recommended” [91]. When bloodborne pathogens other than HBV or HIV are of concern, OSHA continues to require the use of EPA-registered tuberculocidal disinfectants or hypochlorite solution (diluted 1:10 or 1:100 with water) [65,91]. Recent studies demonstrate that, in the presence of large blood spills, a 1:10 final dilution of EPA-registered hypochlorite solution initially should be used to inactivate bloodborne viruses [76,92] to minimize risk of disease to the healthcare worker from percutaneous injury during the clean-up process.

Inactivation of Clostridium difficile

The source of healthcare-associated acquisition of C. difficile in nonepidemic settings has not been determined. The environment and carriage on the hands of healthcare personnel have been considered as possible sources of colonization or infection [93,94]. Carpeted rooms occupied by a patient with C. difficile are more heavily contaminated with C. difficilethan noncarpeted rooms [95]. Because C. difficile may display increased levels of spore production when exposed to non-chlorine-based cleaning agents and the spores are more resistant than vegetative cells to commonly used surface disinfectants [96], some investigators have recommended the use of dilute solutions of hypochlorite (1600 ppm available chlorine) for routine environmental disinfection of rooms of patients with C. difficile–associated diarrhea or colitis [97] to reduce the incidence of C. difficile diarrhea [98] or in units with high C. difficile rates [99]. Stool samples of patients with symptomatic C. difficile colitis must contain spores of the organism because ethanol treatment (active against vegetative bacteria but nor spore) of the stool is used for isolation of C. difficile in the laboratory to reduce the overgrowth by fecal flora [100,101]. Mayfield et al. showed a marked reduction in C. difficile–associated diarrhea rates in a bone-marrow transplant unit (from 8.6 to 3.3 episodes per 1,000 patient-days) during the period of bleach disinfection (1:10 dilution) of environmental surfaces compared to cleaning with a quaternary ammonium compound [99]. Because there are no EPA-registered products specifically approved for inactivating C. difficile spores, use of a diluted hypochlorite should be considered in units with high C. difficile rates. Thus, in units with high endemic C. difficile infection rates or in an outbreak setting, use dilute solutions of 5.25–6.15% sodium hypochlorite (e.g., 1:10 dilution of bleach) for routine environmental disinfection. Acidified bleach and regular bleach (5000 ppm chlorine) can inactivate 10⁶ C. difficile spores in ≤10 minutes [102].

However, studies have shown that asymptomatic patients constitute an important reservoir within the healthcare facility and that person-to-person transmission

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is the principal means of transmission between patients. Thus, handwashing, barrier precautions, and meticulous environmental cleaning with an EPA-registered disinfectant (e.g., germicidal detergent) should be effective in preventing the spread of the organism in endemic situations [103].

Contaminated medical devices, such as colonoscopes and thermometers [104], have served as vehicles for the transmission of C. difficile spores. For this reason, investigators have studied commonly used disinfectants and exposure times to assess whether current practices may be placing patients at risk. Studies demonstrate that 2% glutaraldehyde [105,106,107,108] and peracetic acid [108,109] reliably kill C. difficile spores using exposure times of 5 to 20 minutes. Ortho-phthalaldehyde and ≥0.2% peracetic acid (W. A. Rutala, written communication, April 2006) also can inactivate ≥10⁴ C. difficile spores in 10–12 minutes at 20°C [109].

Susceptibility of Antibiotic-Resistant Bacteria to Disinfectants

Several studies have found antibiotic-resistant hospital strains of common HAI pathogens (i.e., Enterococcus, P. aeruginosa, Klebsiella pneumoniae, E. coli, S. aureus, and S. epidermidis) to be equally susceptible to disinfectants as antibiotic-sensitive strains [110,111,112,113]. The susceptibility of glycopeptide-intermediate S. aureus was similar to vancomycin-susceptible, methicillin-resistant S. aureus [114]. Based on these data, routine disinfection and housekeeping protocols do not need to be altered because of antibiotic resistance provided the disinfection method is effective [115,116]. A study that evaluated the efficacy of selected cleaning methods (e.g., quaternary ammonium [QUAT]-sprayed cloth and QUAT-immersed cloth) for eliminating vancomycin-resistant enterococci (VRE) found that currently used disinfection processes are likely highly effective in eliminating VRE. However, surface disinfection must involve application to all potentially contaminated surfaces [115].

Inactivation of Creutzfeldt-Jakob Disease Agent

Creutzfeldt-Jakob Disease (CJD) is a degenerative neurologic disorder of humans with an incidence in the United States of approximately 1 case/million population/year [117]. CJD is thought to be caused by a proteinaceous infectious agent or prion. CJD is related to other human transmissible spongiform encephalopathies (TSEs) that include kuru (0 incidence, now eradicated), Gertsmann-Straussler-Sheinker syndrome (1/40 million), and fatal insomnia syndrome (FIS) (<1/40 million). The agents of CJD and other TSEs exhibit an unusual resistance to conventional chemical and physical decontamination methods. Because the CJD agent is not readily inactivated by conventional disinfection and sterilization procedures and because of the invariably fatal outcome of CJD, the procedures for disinfection and sterilization of the CJD prion have been both conservative and controversial for many years.

The current recommendations consider inactivation data but also use epidemiological studies of prion transmission, infectivity of human tissues, and efficacy of removing proteins by cleaning. On the basis of scientific data, only critical (e.g., surgical instruments) and semicritical devices contaminated with high-risk tissue (i.e., brain, spinal cord, and eye tissue) from high-risk patients (e.g., known or suspected infection with CJD or other prion disease) require special prion reprocessing. For high-risk tissues, high-risk patients, and critical or semicritical medical devices, one of the following three methods should be used: (1) clean the device and sterilize using a combination of sodium hydroxide and autoclaving [118] (e.g., immerse in 1N NaOH for 1 hour; remove and rinse in water, and then transfer to an open pan and autoclave [121°C gravity displacement or 134°C porous or prevacuum sterilizer] for 1 hour); (2) autoclaving at 134°C for 18 minutes in a prevacuum sterilizer; or (3) 132°C for 1 hour in a gravity displacement sterilizer) [13,119]. The temperature should not exceed 134°C because the effectiveness of autoclaving may decline as the temperature is increased (e.g., 136°C, 138°C) [120]. Prion-contaminated medical devices that are impossible or difficult to clean should be discarded. Flash sterilization (i.e., steam sterilization of an unwrapped item at 132°C for 3 minutes) should not be used for reprocessing. To minimize environmental contamination, noncritical environmental surfaces should be covered with plastic-backed paper, and when contaminated with high-risk tissues, the paper should be properly discarded. Noncritical environmental surfaces (e.g., laboratory surfaces) contaminated with high-risk tissues should be cleaned and then spot decontaminated with a 1:10 dilution of hypochlorite solutions [119].

Emerging Pathogens, Antibiotic-Resistant Bacteria, and Bioterrorism Agents

Emerging pathogens are of growing concern to the general public and infection control professionals. Relevant pathogens include Cryptosporidium parvum, Helicobacter pylori, E. coli O157:H7, HIV, HCV, rotavirus, multidrug-resistant M. tuberculosis, human papilloma virus, norovirus, Severe Acute Respiratory Syndrome (SARS) coronavirus, avian influenza, and nontuberculosis mycobacteria (e.g., M. chelonae). Recent publications have highlighted the concern about the potential for biological terrorism [121]. The CDC has categorized several agents as “high priority” because they can be easily disseminated or transmitted person-to-person, cause high mortality, and are likely to cause public panic and social disruption [122]. These agents include Bacillus anthracis (anthrax), Yersinia pestis (plague), variola major (smallpox), Francisella tularensis (tularemia),

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filoviruses (Ebola hemorrhagic fever, Marburg hemorrhagic fever); and arenaviruses (Lassa [Lassa fever], Junin [Argentine hemorrhagic fever]), and related viruses [122].

With rare exceptions (e.g., human papilloma virus), the susceptibility of each of these pathogens to chemical disinfectants/sterilants has been studied and all of these pathogens (or surrogate microbes) such as feline-calicivirus for norovirus, vaccinia for variola [123], and B. atrophaeus (formerly B. subtilis) for B. anthracis, are susceptible to currently available chemical disinfectants/sterilants [124]. Standard sterilization and disinfection procedures for patient-care equipment (as recommended in this chapter) are adequate to sterilize or disinfect instruments or devices contaminated with blood or other body fluids from persons infected with bloodborne pathogens, emerging pathogens, and bioterrorism agents with the exception of prions (see previous comment). No changes in procedures for cleaning, disinfecting, or sterilizing need to be made for equipment [13].

In addition, there are no data to show that antibiotic-resistant bacteria (methicillin-resistant Staphylococcus aureus [MRSA], VRE, multidrug-resistant M. tuberculosis) are less sensitive to the liquid chemical germicides than antibiotic-sensitive bacteria at currently used germicide contact conditions and concentrations [110,125].

Advances in Disinfection and Sterilization Methods

In the past several years, new methods of disinfection and sterilization have been introduced in the healthcare setting. Ortho-phthalaldehyde (OPA) is a chemical sterilant that received FDA clearance in October 1999. It contains 0.55% 1,2-benzenedicarboxaldehyde. Studies have demonstrated excellent microbicidal activity in in vitro studies [13]. For example, Gregory et al. demonstrated that OPA has superior mycobactericidal activity (5-log₁₀ reduction in 5 minutes) compared to glutaraldehyde [126]. The advantages, disadvantages, and characteristics of OPA are listed in Tables 20-2 and 20-3.

The FDA recently cleared a liquid high-level disinfectant (i.e., superoxidized water) that contains 650–675 ppm free chlorine, two chemical sterilants (i.e., 3.4% glutaraldehyde with 0.26% isopropanol, and 8.3% hydrogen peroxide with 7.0% peracetic acid) and a new sterilization system using ozone. Some of these processes may not be commercially available (e.g., 3.4% glutaraldehyde with 0.26% isopropanol, and 8.3% hydrogen peroxide with 7.0% peracetic acid), or there are only limited data in the scientific literature that assess the antimicrobial activity or material compatibility of these processes, so they have not yet been commonly integrated into clinical practice in the United States [13].

Several methods are used to sterilize patient-care items in healthcare, including steam sterilization, ethylene oxide, hydrogen peroxide gas plasma, and a peracetic acid immersion system. The advantages and disadvantages of these systems are listed in Table 20-4 [13].

New sterilization technology based on plasma was patented in 1987 and marketed in the United States in 1993. Gas plasmas have been referred to as the fourth state of matter (i.e., liquids, solids, gases, and gas plasmas). They are generated in an enclosed chamber under deep vacuum using radiofrequency or microwave energy to excite the gas molecules and produce charged particles, many of which are in the form of free radicals. This process has the ability to inactivate a broad spectrum of microorganisms, including resistant bacterial spores. Studies have been conducted against vegetative bacteria (including mycobacteria), yeasts, fungi, viruses, and bacterial spores [13]. The effectiveness of all sterilization processes can be altered by lumen length, lumen diameter, inorganic salts, and organic materials [13].

Conclusion

When properly used, disinfection and sterilization can ensure the safe use of invasive and non invasive medical devices. The method of disinfection and sterilization depends on the intended use of the medical device: Critical items (contact sterile tissue) must be sterilized before use; semicritical items (contact mucous membranes or nonintact skin) must be high-level disinfected; and noncritical items (contact intact skin) should receive low-level disinfection. Cleaning should always precede high-level disinfection and sterilization. Current disinfection and sterilization guidelines must be strictly followed to prevent HAIs.

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