Disinfection and Sterilization in Healthcare Facilities

William A. Rutala

David J. Weber

INTRODUCTION

In the United States in 2009, there were approximately 48,000,000 surgical procedures and an even larger number of invasive medical procedures (1). For example, there are about 11 million gastrointestinal endoscopies performed per year (2). 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, which can lead to infection. For example, failure to properly disinfect or sterilize equipment may lead to transmission via contaminated instruments or devices (e.g., Mycobacterium 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. Since 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 (3,4). Failure to comply with scientifically based guidelines has led to numerous outbreaks (4,5,6,7,8,9). In this updated chapter (10,11,12,13), a pragmatic approach to the judicious selection and proper use of disinfection and sterilization processes is presented, based on well-designed studies assessing the efficacy (via laboratory investigations) and effectiveness (via clinical studies) of disinfection and sterilization procedures.

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, hydrogen peroxide vapor, ozone, 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 fungal and 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 is usually accomplished by the use of liquid chemicals or wet pasteurization in health care 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 nature of the object (e.g., crevices, hinges, and 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., ETO).

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 to 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 will kill all microorganisms with the exception of large numbers of bacterial spores and are called high-level disinfectants. Low-level disinfectants may 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 (Table 20.1).

Cleaning, on the other hand, is the removal of visible soil (e.g., organic and inorganic material) from objects and surfaces, and it normally is accomplished by manual or mechanical means using water with detergents or enzymatic products. Thorough cleaning is essential before high-level disinfection and sterilization, since inorganic and organic materials that remain on the surfaces of instruments interfere with the effectiveness of these processes. Decontamination is a procedure that removes pathogenic microorganisms from objects so they are safe to handle, use, or discard.

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 only used on the skin and 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 (14,15,16,17,18,19,20).

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 items¹ and noncritical items)	Low-level (noncritical items; will come in contact with intact skin)
Object	Procedure	Exposure Time	Procedure (exposure time 12-30 minutes at ≥20°C)²,³	Procedure (exposure time ≥ 1 minute)⁹	Procedure (exposure time ≥ 1 minute)⁹
Smooth, hard surface¹,⁴	A	MR	D
	B	MR	E	L⁵	L
	C	MR	F	M	M
	D	10 hours at 20°-25°C	H	N	N
	F	6 hours	I⁶	P	O
	G¹⁰	12 minutes at 50°-56°C	J	Q	P
			K		Q
	H	3-8 hours
Rubber tubing and catheters³,⁴	A	MR	D
	B	MR	E
	C	MR	F
	D	10 hours at 20°-25°C	H
	F	6 hours	I⁶
	G	12 minutes at 50°-56°C	J
	H	3-8 hours	K
Polyethylene tubing and catheters³,⁴,⁷	A	MR	D
	B	MR	E
	C	MR	F
	D	10 hours at 20°-25°C	H
	F	6 hours	I⁶
	G	12 minutes at 50°-56°C	J
	H	3-8 hours	K
Lensed instruments⁴	A	MR	D
	B	MR	E
	C	MR	F
	D	10 hours at 20°-25°C	H
	F	6 hours	J
	G	12 minutes at 50°-56°C	K
	H	3-8 hours
Thermometers (oral and rectal)⁸				P⁸
Hinged instruments⁴	A	MR	D
	B	MR	E
	C	MR	F
	D	10 hours at 20°-25°C	H
	F	6 hours	I⁶
	G	12 minutes at 50°-56°C	J
	H	3-8 hours	K
The selection and use of disinfectants in the healthcare field is dynamic, and products may become available that are not in existence when this chapter 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 to 30 minutes)
B Ethylene oxide gas (see manufacturer’s recommendations, generally 1 to 6 hours processing time plus aeration time of 8 to 12 hours at 50°C to 60°C)
C Hydrogen peroxide gas plasma (see manufacturer’s recommendations for internal diameter and length restrictions, processing time between 28 to 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%) with 1.93% phenol/phenate; and glutaraldehyde (3.4%) with isopropanol (26%). 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, standard 7.5% (will corrode copper, zinc, and brass)
G Peracetic acid, concentration variable, but 0.2% or greater is sporicidal. A 0.2% peracetic acid immersion reprocessor operates at 50°C to 56°C. Per guidance from the FDA, most hospitals use the 0.2% peracetic acid reprocessor for reprocessing semicritical items that require high-level disinfection. Thus, as a general rule, the reprocessor will not be used to reprocess critical items, as critical items should be sterile and with the reprocessor using 0.2% peracetic acid the final processed device cannot be assured to be sterile. Thus, heat-sensitive critical devices should be sterilized by other validated, FDA-cleared, sterilization processes such as hydrogen peroxide gas plasma, ETO, vaporized hydrogen peroxide, and ozone. If a heat-sensitive critical device truly cannot be processed by any other modality than the reprocessor using 0.2% peracetic acid then we are left with the decision between not using the device at all or reprocessing it in the 0.2% peracetic acid reprocessor (at 50°C to 56°C). The decision to use the 0.2% peracetic reprocessor at 50°C to 56°C for a heat-sensitive critical item that cannot be processed by an alternative sterilization process should be made on a case-by-case basis.
H Hydrogen peroxide (7.35%) with 0.23% peracetic acid; hydrogen peroxide 1% with peracetic acid 0.08%; 8.3% hydrogen peroxide, and 7.0% 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 ≥400-675 active free chlorine; (will corrode metal instruments) K Improved hydrogen peroxide, ≥2%
L Sodium hypochlorite (5.25% to 6.15% household bleach diluted 1:500 provides > 100 ppm 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)
P Ethyl and isopropyl alcohol
Q Improved hydrogen peroxide. 0.5% and 1.4%
MR, Manufacturer’s recommendations; NA, Not applicable
¹See text for discussion of hydrotherapy. ²The longer the exposure to a disinfectant, the more likely it is that all microorganisms will be eliminated. 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 5 minutes at 25°C in automated endoscope reprocessor). ³Tubing must be completely filled for high-level disinfection and liquid chemical sterilization; care must be taken to avoid entrapment of air bubbles during immersion. ⁴Material compatibility should be investigated when appropriate. ⁵A concentration of 1000 parts per million (ppm) 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 > 1000 ppm available chlorine). This solution may corrode some surfaces. ⁶Pasteurization (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. ⁷Thermostability should be investigated when appropriate. ⁸Do not mix rectal and oral thermometers at any stage of handling or processing. ⁹By law, all applicable label instructions on EPA-registered products must be followed. If the user selects exposure conditions that differ from those on the EPA-registered products label, the user assumes liability from any injuries resulting from off-label use and is potentially subject to enforcement action under FIFRA. Modified from Simmons BP. CDC guidelines for the prevention and control of nosocomial infections. Guideline for hospital environmental control. Am J Infect Control. 1983;11:97-120, with permission. Modified from Rutala WA, APIC Guidelines Committee. APIC guideline for selection and use of disinfectants. Association for Professionals in Infection Control and Epidemiology, Inc. Am J Infect Control. 1996;24:313-342, with permission. Modified from Rutala WA. Disinfection, sterilization and waste disposal. In: Wenzel RP, ed. Prevention and Control of Nosocomial Infections. 3rd ed. Baltimore, MD: Williams and Wilkins; 1997:539-593, with permission. Modified from Rutala WA, Weber DJ, Healthcare Infection Control Practices Advisory Committee. Guideline for disinfection and sterilization in healthcare facilities, 2008. cdc.gov/ncidod/dhqp/pdf/guidelines/Disinfection_Nov_2008.pdf, with permission. Modified from Rutala WA. Selection and use of disinfectants in healthcare. In: Mayhall CG, ed. Hospital Epidemiology and Infection Control. 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2012:1180-1212, with permission. ¹⁰Per guidance from the FDA, most hospitals use the 0.2% peracetic acid reprocessor for reprocessing semicritical items that require high-level disinfection (see G above).

A RATIONAL APPROACH TO DISINFECTION AND STERILIZATION

Over 45 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 preventionists and others when planning methods for disinfection or sterilization (14,16,18,20,21,22,23). 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. Although the scheme remains valid, there are some examples of disinfection studies with viruses, mycobacteria and protozoa that challenge the current definitions and expectations of high- and low-level disinfection (24,25). The Spaulding terminology is employed by the Centers for Disease Control and Prevention’s (CDC’s) “Guidelines for Environmental Infection Control in Healthcare Facilities” (26) and “Guideline for Disinfection and Sterilization in Healthcare Facilities” (20).

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 disease transmission. This category includes surgical instruments; cardiac, intravascular 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 ETO, hydrogen peroxide gas plasma, vaporized hydrogen peroxide, ozone, or by liquid chemical sterilants if other methods are unsuitable. Tables 20.1 and 20.2 list several germicides categorized as chemical sterilants. These include: ≥2.4% glutaraldehyde-based formulations, 1.12% glutaraldehyde with 1.93% phenol/phenate, 3.4% glutaraldehyde with 26% isopropanol, 0.55% ortho-phthalaldehyde, 7.5% standard hydrogen peroxide, 2% improved hydrogen peroxide, 400 to 675 parts per million (ppm) hypochlorite/hypochlorous acid, 7.35% hydrogen peroxide with 0.23% peracetic acid, 0.2% peracetic acid, 8.3% hydrogen peroxide with 7.0% peracetic acid, and 1.0% hydrogen peroxide with 0.08% peracetic acid. With the exception of 0.2% peracetic acid (12 minutes at 50° to 56°C), the indicated exposure times for sterilization range from 3 to 12 hours.²⁷ Liquid chemical sterilants can be relied upon to produce sterility only if cleaning, which eliminate organic and inorganic material, precedes treatment and if proper guidelines as to 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, 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. Semicritical items minimally require high-level disinfection using chemical disinfectants. Glutaraldehyde (with and without other active ingredients), standard hydrogen peroxide, ortho-phthalaldehyde, peracetic acid with hydrogen peroxide, improved hydrogen peroxide, and chlorine are cleared by the U.S. Food and Drug Administration (FDA) (27) and are dependable high-level disinfectants, provided the factors influencing germicidal procedures are met. The exposure time for most high-level disinfectants varies from 8 to 45 minutes at 20° to 25°C. Outbreaks occur when ineffective disinfectants, including iodophor, alcohol, and over-diluted 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, October 15, 1999, written communication). Similarly, Olympus does not endorse the use of the hydrogen peroxide with peracetic acid products due to cosmetic and functional damage (Olympus America, April 15, 1998 and September 13, 2000, written communication).

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 (20,28,29). 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 (29). 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, anoscopes) or vagina (e.g., vaginal probes) (20).

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, linens, bedside tables, patient furniture, and floors. In contrast to critical and some semicritical items, most non-critical 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 (30) when they are used as noncritical items and do not contact nonintact skin and/or mucous membranes. However, these items (e.g., bedside tables, bed rails) do contribute to secondary transmission by contaminating hands of healthcare workers or by contact with medical equipment that will subsequently come in contact with patients (31,32). Table 20.1 lists several low-level disinfectants that may be used for noncritical items. The exposure time listed in Table 20.1 is at least 60 seconds.

TABLE 20.2 Summary of Advantages and Disadvantages of Chemical Agents Used as Chemical Sterilants^a or as High-Level Disinfectants (HLD)

Sterilant/HLD	Advantages	Disadvantages
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 (unless other disinfectants added such as phenolic, alcohol) Coagulates blood and fixes tissue to surfaces Allergic contact dermatitis
Hydrogen Peroxide, standard	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 Efficacy data published 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 Reported to cause anaphylactic-like reactions in bladder cancer patients undergoing repeated cystoscopy
Peracetic Acid	Rapid cycle time (30-45 minutes) Low temperature (50°-55°C) liquid immersion Environmental friendly by-products (acetic acid, O₂, H₂O) 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 long-term storage
Improved hydrogen peroxide (≥ 2.0%)	No activation required No odor Nonstaining No special venting requirements Manual or automated applications 12 month shelf life, 14 day reuse 8 minutes at 20°C high-level disinfectant claim	Material compatibility concerns due to limited clinical experience Organic material resistance concerns due to limited data Limited clinical use and comparative microbicidal efficacy data
^aAll products effective in presence of organic soil, relatively easy to use, and have a broad spectrum of antimicrobial activity (bacteria, fungi, viruses, spores, and mycobacteria). The above characteristics are documented in the literature; contact the manufacturer of the instrument and sterilant for additional information. Modified from Rutala WA, Weber DJ. Sterilization, high-level disinfection, and environmental cleaning. Infect Dis Clin North Am. 2011;25:45-76, with permission. Modified from Rutala WA, Weber DJ. Sterilization and disinfection. In: Jarvis WR, ed. Bennett and Brachman’s Hospital Infections. 5th ed. Philadelphia, PA: Wolter Kluwer/Lippincott Williams & Wilkins; 2007:303-318, with permission. Modified from Rutala WA, Weber DJ. Disinfection of endoscopes: review of new chemical sterilants used for high-level disinfection. Infect Control Hosp Epidemiol. 1999;20:69-76, with permission.

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 since 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 is 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.

Instrument cleaning is done manually when the use area does not have a mechanical unit (e.g., ultrasonic cleaner, or washer-disinfector), or 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 (33). 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.

The most common types of mechanical or automatic cleaners include ultrasonic cleaners, washer-decontaminators, washer-disinfectors, and washer-sterilizers. Ultrasonic cleaning removes soil by a process called cavitation and implosion in which waves of acoustic energy are propagated in aqueous solutions to disrupt the bonds that hold particulate matter to surfaces. Bacterial contamination may be present in used ultrasonic cleaning solutions (and other used detergent solutions) as these solutions generally do not make antibacterial label claims (34). While ultrasound alone does not cause significant inactivation of bacteria, sonication can act synergistically to increase the cidal efficacy of a disinfectant (35). Users of ultrasonic cleaners should be aware that the cleaning fluid could result in endotoxin contamination of surgical instruments that could cause severe inflammatory reactions (36). Washer-sterilizers are modified steam sterilizers that clean by filling the chamber with water and detergent through which steam is passed to provide agitation. Instruments are subsequently rinsed and subjected to a short steam sterilization cycle. Another washer-sterilizer employs rotating spray arms for a wash cycle followed by a steam sterilization cycle at 285°F (37,38). Washer-decontaminators/disinfectors act like a dishwasher that uses a combination of water circulation and detergents to remove soil. These units sometimes have a cycle that subjects the instruments to a heat process (e.g., 93°C for 10 minutes) (39). Washer-disinfectors are generally computer-controlled units for cleaning, disinfecting, and drying solid and hollow surgical and medical equipment. In one study, cleaning (measured as 5- to 6-log₁₀ reduction) was achieved on surfaces that were adequately in contact with the water flow in the machine (40). Detailed information on cleaning and preparation of supplies for terminal sterilization is provided by professional organizations (41,42) and books (43). Studies have shown that manual and mechanical cleaning of endoscopes achieves a 4-to 6-log₁₀ reduction of contaminating organisms (44,45,46,47). Thus, cleaning alone is very effective in reducing the number of microorganisms present on contaminated equipment. When manual methods are compared to automated methods for cleaning reusable accessory devices used for minimally invasive surgical procedures, the automated method was more efficient and achieved a >99% reduction in soil parameters (i.e., protein, carbohydrate, hemoglobin) in both ported and nonported laparoscopic devices (48).

The choice for instrument cleaning is neutral or near-neutral pH detergent solutions, as these solutions generally provide the best material compatibility profile and good soil removal. Enzymes, usually proteases, are sometimes added to neutral pH solutions to assist in the removal of organic material. Enzymes in these formulations attack proteins that make up a large portion of common soil (e.g., blood, pus). Cleaning solution also can contain lipases (enzymes active on fats) and amylases (enzymes active on starches). Enzymatic cleaners are not disinfectants, and proteinaceous enzymes may be inactivated by germicides. Like all chemicals, enzymes must be rinsed from the equipment, or adverse reactions (e.g., fever) could result (49). Enzyme solutions should be used in accordance with manufacturer’s instructions. Detergent enzymes may be associated with asthma or other allergic effects in users. Neutral pH detergent solutions that contain enzymes are compatible with metals and other materials used in medical instruments and are the best choice for cleaning delicate medical instruments, especially flexible endoscopes (46). Alkaline-based cleaning agents are used for processing medical devices as they dissolve protein and fat residues efficiently (50); however, they may be corrosive (46). Some data demonstrate that enzymatic cleaners are more effective cleaners than neutral detergents (51,52) in removing microorganisms from surfaces, but two studies found no difference in cleaning efficiency between enzymatic and alkaline-based cleaners (50,53). A new nonenzyme, hydrogen peroxide-based formulation (not FDA cleared) was as effective as enzymatic cleaners in removing protein, blood, carbohydrate, and endotoxin from surface test carriers (54). In addition, this product was
able to effect a 5-log₁₀ reduction in microbial loads with a 3-minute exposure at room temperature (54). Although the effectiveness of high-level disinfection and sterilization mandates effective cleaning, there are no “real-time” tests that can be employed in a clinical setting to verify cleaning. If such tests were commercially available they could be used to ensure that an adequate level of cleaning has been done (55,56,57,58). The only way to ensure adequate cleaning is to conduct a reprocessing verification test (e.g., microbiologic sampling), but this is not routinely recommended (59). Validation of the cleaning processes in a laboratory-testing program is possible by microorganism detection, chemical detection for organic contaminants, radionuclide tagging, and chemical detection for specific ions (57,60). Data has been published describing the use of an artificial soil, protein, endotoxin, X-ray contrast medium, or blood to verify the manual or automated cleaning process (40,61,62,63,64,65) and adenosine triphosphate (ATP) bioluminescence, fluoresence and microbiologic sampling to evaluate the effectiveness of environmental surface cleaning (66,67,68). Although ATP has been suggested for assessing the cleanliness of instruments, it has not been validated for this use. Minimally, all instruments should be individually inspected and be visibly clean.

Toxic anterior segment syndrome (TASS) is an acute inflammation of the anterior chamber, or segment, of the eye following cataract surgery. A variety of substances have been implicated as causes of TASS and includes impurities of autoclave steam, heat-stable endotoxin, and irritants on the surfaces of intraocular surgical instruments. General principles of cleaning and sterilizing intraocular surgical instruments have been published (69).

DISINFECTION

A great number of disinfectants are used alone or in combinations (e.g., hydrogen peroxide with peracetic acid) in the healthcare setting. These include alcohols, chlorine and chlorine compounds, formaldehyde, glutaraldehyde, orthophthalaldehyde, hydrogen peroxide (standard), improved hydrogen peroxide, iodophors, peracetic acid, phenolics, and quaternary ammonium compounds (QUAT). Commercial formulations based on these chemicals are considered unique products and must be registered with the U.S. 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 efficient manner.

Disinfectants are not interchangeable, and an overview of the performance characteristics is provided (Table 20.2), so the user has sufficient information to select an appropriate disinfectant for any item and use it in the most efficient way. 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 taken to minimize exposure (70,71,72). Asthma and reactive airway disease may occur in sensitized individuals exposed to any airborne chemical including germicides. Clinically important asthma may occur at levels below ceiling levels regulated by the U.S. Occupational Safety and Health Administration (OSHA) or recommended by CDC’s National Institute of Occupational Safety and Health (NIOSH). The preferred method of control is to eliminate the chemical (via engineering controls, or substitution) or relocate the worker.

STERILIZATION

Most medical and surgical devices used in healthcare facilities are made of materials that are heat-stable and thus are 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. ETO has been used since the 1950s for heat- and moisture-sensitive medical devices. Within the past 25 years, a number of new, low-temperature sterilization systems (e.g., hydrogen peroxide gas plasma, hydrogen peroxide vapor, ozone) have been developed and are being used to sterilize medical devices. Table 20.3 reviews sterilization technologies used in healthcare and makes recommendations for their optimum performance in the processing of medical devices (20,73).

Sterilization destroys all microorganisms on the surface of an article or in a fluid to prevent pathogen 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 (74,75,76

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