Selection and Use of Disinfectants in Healthcare

William A. Rutala

David J. Weber

Each year in the United States there are 46 million procedures performed on hospital inpatients and an estimated 53.3 million surgical and nonsurgical procedures performed during ambulatory surgery visits (1,2). For example, there are at least 10 million gastrointestinal endoscopies per year (3). Each of these procedures involves contact by a medical device or a surgical instrument with a patient’s sterile tissue or mucous membranes. A major risk of all such procedures is the introduction of infection. Failure to properly disinfect or sterilize equipment carries not only the risk associated with breach of the host barriers but also the additional risk of person-to-person transmission (e.g., hepatitis B virus) and transmission of environmental pathogens (e.g., Pseudomonas aeruginosa).

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 unnecessary to sterilize all patient-care items, healthcare policies must identify whether cleaning, disinfection, or sterilization is indicated based primarily on the items’ intended use.

Multiple studies in many countries have documented lack of compliance with established guidelines for disinfection and sterilization (4,5). Failure to comply with scientifically based guidelines has led to numerous outbreaks (5, 6, 7, 8 and 9). In this chapter, which is an update of previous chapters (10,11,12,13, 14, 15 and 16), a pragmatic approach to the judicious selection and proper use of disinfection processes is presented. This is 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 is the complete elimination or destruction of all forms of microbial life and is accomplished in healthcare facilities by either physical or chemical processes. Steam under pressure, dry heat, ethylene oxide (ETO) gas, hydrogen peroxide gas plasma, ozone, hydrogen peroxide vapor, and liquid chemicals are the principal sterilizing agents used in healthcare facilities. Sterilization is intended to convey an absolute meaning, not a relative one.

Unfortunately, some health professionals as well as the technical and commercial literature refer to “disinfection” as “sterilization” and items as “partially sterile.” When chemicals are used for the purpose 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 may also 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 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 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 cases, the relative humidity of the sterilization process (e.g., with 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 (e.g., 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 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 80-1 is discussed later and consulted in this context.

TABLE 80-1 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 Nonintack Skin)*	*Intermediate-Level (Some Semicritical Items^a 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)*^b,^c	*Procedure (Exposure Time ≥1 m)*^d	*Procedure (Exposure Time ≥ 1 m)*^d
Smooth, hard Surface^a,^e	A	MR	D	K	K
Smooth, hard Surface^a,^e	B	MR	E	L^f	L
	C	MR	F	M	M
	D	10 h at 20-25°C	H	N	N
	F	6 h	I^g		O
	G	12 m at 50-56°C	J		P
	H	3-8 h
Rubber tubing and catheters^c,^e	A	MR	D
Rubber tubing and catheters^c,^e	B	MR	E
	C	MR	F
	D	10 h at 20-25°C	H
	F	6 h	I^g
	G	12 m at 50-56°C	J
	H	3-8 h
Polyethylene tubing and catheters^c,^e,^h	A	MR	D
Polyethylene tubing and catheters^c,^e,^h	B	MR	E
	C	MR	F
	D	10 h at 20-25°C	H
	F	6 h	I^g
	G	12 m at 50-56°C	J
	H	3-8 h
Lensed instruments^e	A	MR	D
	B	MR	E
	C	MR	F
	D	10 h at 20-25°C	H
	F	6 h	I^g
	G	12 m at 50-56°C	J
	H	3-8 h
Thermometers (oral and rectal)ⁱ				K^h
Hinged instruments^e	A	MR	D
	B	MR	E
	C	MR	F
	D	10 h at 20-25°C	H
	F	6 h	I^g
	G	12 m at 50-56°C	J
	H	3-8 h
^aSee text for discussion of hydrotherapy. ^bThe 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 min 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 min at 35°C, 0.55% OPA at 5 min at 25°C in automated endoscope reprocessor). ^cTubing must be completely filled for high-level disinfection and liquid chemical sterilization; care must be taken to avoid entrapment of air bubbles during immersion. ^dBy 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. ^eMaterial compatibility should be investigated when appropriate. ^fA concentration of 1,000 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 >1,000 ppm available chlorine). This solution may corrode some surfaces. ^gPasteurization (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. ^hThermostability should be investigated when appropriate. ⁱDo not mix rectal and oral thermometers at any stage of handling or processing.
The selection and use of disinfectants in the health-care field is dynamics, 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 min). B, Ethylene oxide gas (see manufacturer’s recommendations, generally 1-6 h processing time plus aeration time of 8-12 h at 50-60°C). C, Hydrogen peroxide gas plasma (see manufacturer’s recommendations for internal diameter and length restrictions, processing time between 28 and 72 min), ozone, and hydrogen peroxide vapor (see manufacturer’s recommendations for internal diameter and length restrictions). 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; glutaraldehyde (3.4%) with 26% isopropanol. One glutaraldehyde-based product has a high-level disinfection claim of 5 min at 35°C. E, Ortho-phthalaldehyde (OPA) ≥0.55% F, Hydrogen peroxide 7.5% (will corrode copper, zinc, and brass) and 2.0% accelerated hydrogen peroxide. G, Peracetic acid, concentration variable but 0.2% or greater is sporicidal. Peracetic acid immersion system operates at 50-56°C. This liquid chemical sterilant processing system should be used only for processing heat-sensitive semicritical and critical devices that are compatible with the sterilant and processing system and cannot be sterilized by other fully validated terminal sterilization methods for the device. H, Hydrogen peroxide (7.35%) plus 0.23% peracetic acid; hydrogen peroxide 8.3% plus peracetic acid 7.0%; hydrogen peroxide 1% plus peracetic acid 0.08% (will corrode metal instruments). I, Wet pasteurization at 70°C for 30 min 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 >100 ppm available chlorine). M, Phenolic germicidal detergent solution (follow product label for use-dilution). N, Lodophor germicidal detergent solution (follow product label for use-dilution). O, Quaternary ammonium germicidal detergent solution (follow product label for use-dilution). P, Accelerated hydrogen peroxide 0.5% (follow product label). MR, Manufacturer’s recommendations. NA, Not applicable.

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 (17). 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. 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. 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 microorganisms (“germs”). The term germicide includes both antiseptics and disinfectants. Antiseptics are germicides applied to living tissue and skin, whereas 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 rarely 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 (18, 19, 20, 21, 22 and 23).

A RATIONAL APPROACH TO DISINFECTION AND STERILIZATION

Over 40 years ago, Earle H. Spaulding (19) 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 (10,11,18,20,22,24,25). 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.

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 and urinary catheters, implants, and ultrasound probes used in sterile body cavities. Most of the items in this category should be purchased as sterile or be sterilized by steam sterilization if possible. If heatsensitive, the object may be treated with ETO, hydrogen peroxide gas plasma, ozone, hydrogen peroxide vapor, or by liquid chemical sterilants if other methods are unsuitable. Table 80-1 lists several germicides categorized as chemical sterilants. These include ≥2.4% glutaraldehydebased formulations; hypochlorous acid/hypochlorite 650 to 675 ppm free chlorine (or 400-450 ppm free chlorine at 30°C); 1.12% glutaraldehyde with 1.93% phenol/phenate; 3.4% glutaraldehyde with 26% isopropanol (26); 7.5% hydrogen peroxide; 7.35% hydrogen peroxide with 0.23% peracetic acid; 8.3% hydrogen peroxide with 7.0% peracetic acid; 0.2% peracetic acid; ≥0.55% ortho-phthalaldehyde; 2.0% accelerated hydrogen peroxide; and 1.0% hydrogen peroxide with 0.08% peracetic acid (27). Liquid chemical sterilants can be relied upon to produce sterility only if cleaning, to eliminate organic and inorganic material, precedes treatment and if proper guidelines as to concentration, contact time, temperature, and pH are met.

Semicritical Items

Semicritical items are those that come in contact with mucous membranes or nonintact skin. Respiratory therapy and anesthesia equipment, gastrointestinal endoscopes, bronchoscopes, laryngoscope blades, esophageal manometry probes, endocavitary probes, anorectal manometry catheters, infrared coagulation probes, cystoscopes (28), and diaphragm fitting rings are included in this category. These medical devices should be free of all microorganisms, 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 microorganisms such as bacteria, mycobacteria, and viruses. Semicritical items minimally require high-level disinfection using chemical disinfectants. Glutaraldehyde, hydrogen peroxide, ortho-phthalaldehyde, and peracetic acid with or without hydrogen peroxide are cleared by the Food and Drug Administration (FDA) and are dependable high-level disinfectants provided the factors influencing germicidal procedures are met (Table 80-1) (27). 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.

The complete elimination of all microorganisms in or on an instrument with the exception of small numbers of bacterial spores is the traditional definition of high-level disinfection. FDA’s definition of high-level disinfection is a sterilant used for a shorter contact time to achieve a 6-log₁₀ kill of an appropriate mycobacterium species. Cleaning followed by high-level disinfection should eliminate sufficient pathogens to prevent transmission of infection (29,30).

Laparoscopes and arthroscopes entering sterile tissue should be sterilized between patients. As with flexible endoscopes, these devices may be difficult to clean and sterilize due to intricate device design (e.g., long narrow lumens, hinges). Meticulous cleaning must precede any sterilization process. Newer models of these instruments can withstand steam sterilization.

Semicritical items should be rinsed with sterile water after high-level disinfection to prevent their contamination with microorganisms that may be present in tapwater, such as nontuberculous mycobacteria (9,31), Legionella (32,33), or gram-negative bacilli such as Pseudomonas (22,24,34, 35 and 36). In circumstances where rinsing with sterile water rinse is not feasible, a tapwater or filtered water (0.2-µm filter) rinse should be followed by an alcohol rinse and forced air drying (11,36, 37, 38 and 39). Forced air drying markedly reduces bacterial contamination of stored endoscopes, most likely by removing the wet environment favorable for bacterial growth (37). After rinsing, items should be dried and stored (e.g., packaged) in a manner that protects them from recontamination.

Some items that may come in contact with nonintact skin for a brief period of time (i.e., hydrotherapy tanks, bed side rails) are usually considered noncritical surfaces and are disinfected with low- or intermediate-level disinfectants (i.e., phenolic, iodophor, alcohol, chlorine) (40). Since hydrotherapy tanks have been associated with spread of infection, some facilities have chosen to disinfect them with recommended levels of chlorine (40).

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, bedside tables, patient furniture, and floors. The five most commonly touched items in the patient environment have been quantitatively shown to be bed rails, bed surface, supply cart, overbed table, and IV pump (41). 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 (35) 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) 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 (18,42, 43, 44 and 45). Table 80-1 lists several low-level disinfectants that may be used for noncritical items. The exposure time listed in Table 80-1 is equal to or >1 minute. Most Environmental Protection Agency (EPA)-registered disinfectants have a 10-minute label claim. However, multiple investigators have demonstrated the effectiveness of these disinfectants against vegetative bacteria (e.g., Listeria, Escherichia coli, Salmonella, vancomycin-resistant enterococci [VRE], methicillin-resistant Staphylococcus aureus [MRSA]), yeasts (e.g., Candida), mycobacteria (e.g., Mycobacterium tuberculosis), and viruses (e.g. poliovirus) at exposure times of <60 seconds (42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56 and 57). Thus, it is acceptable to disinfect noncritical medical equipment (e.g., blood pressure cuff) and noncritical surfaces (e.g., bedside table) with an EPA-registered disinfectant or disinfectant/detergent at the proper use dilution and a contact time of at least 1 minute (58). Since the typical drying time for a germicide on a surface is 1 to 3 minutes (unless the product contains alcohol [e.g., a 60-70% alcohol will dry in about 30 seconds])(N. Omidbakhsh, written communication), one application of the germicide on all surfaces to be disinfected is recommended.

Mops (microfiber and cotton-string), reusable cleaning cloths, and disposable wipes are regularly used to achieve low-level disinfection (59,60). Microfiber mops have demonstrated superior microbial removal compared with cotton string mops when used with detergent cleaner (95% vs. 68%, respectively). Use of a disinfectant did significantly improve microbial removal when a cotton string mop was used (95% vs. 95%, respectively) (60). Mops (especially cotton-string mops) are commonly not kept adequately cleaned and disinfected, and if the water-disinfectant mixture is not changed regularly (e.g., after every three to four rooms, no longer than 60-minute intervals), the mopping procedure may actually spread heavy microbial contamination throughout the healthcare facility (61). In one study, standard laundering provided acceptable decontamination of heavily contaminated mopheads, but chemical disinfection with a phenolic was less effective (61). The frequent laundering of cotton-string mops (e.g., daily) is, therefore, recommended.

Hospital cleanliness continues to attract patient attention and in the United States it is still primarily assessed via visual appearance, which is not a reliable indicator of surface cleanliness (62). Three other methods have been offered for monitoring patient room hygiene and they include adenosine triphosphate (ATP) bioluminescence (63,64); fluorescent markers (65,66); and microbiologic sampling (64). Studies have demonstrated suboptimal cleaning was documented by aerobic colony counts as well as the use of the ATP bioluminescence and fluorescent markers.

FACTORS AFFECTING THE EFFICACY OF DISINFECTION AND STERILIZATION

The activity of germicides against microorganisms depends on a number of factors, some of which are intrinsic qualities of the microorganism, while others depend on the chemical and external physical environment. An awareness of these factors should lead to a better utilization of disinfection and sterilization processes; thus, they will be briefly reviewed. More extensive consideration of these and other factors may be found in the references for this section (18,19,21,67, 68 and 69).

Number and Location of Microorganisms

All other conditions remaining constant, the larger the number of microbes present, the longer it takes for a germicide to destroy all of them. This relationship was illustrated by Spaulding when he employed identical test conditions and demonstrated that it took 30 minutes to kill 10 Bacillus atrophaeus (formerly B. subtilis) spores but 3 hours to kill 100,000 B. atrophaeus spores. This reinforces the need for scrupulous cleaning of medical instruments before disinfection and sterilization. Reducing the number of microorganisms that must be inactivated through meticulous cleaning increases the margin of safety when the germicide is used according to the labeling and shortens the exposure time required to kill the entire microbial load. Researchers have also shown that aggregated or clumped cells are more difficult to inactivate than monodispersed cells (70).

The location of microorganisms also must be considered when assessing factors affecting the efficacy of germicides. Medical instruments with multiple pieces must be disassembled and equipment such as endoscopes that have crevices, joints, and channels are more difficult to disinfect than flat-surface equipment because it is more difficult to penetrate all parts of the equipment with a disinfectant. Only surfaces in direct contact with the germicide will be disinfected, so there must be no air pockets and the equipment must be completely immersed for the entire exposure period. Manufacturers should be encouraged to produce equipment that is engineered, so cleaning and disinfection may be accomplished with ease.

Innate Resistance of Microorganisms

Microorganisms vary greatly in their resistance to chemical germicides and sterilization processes (Fig. 80-1) (71). Intrinsic resistance mechanisms in microorganisms to disinfectants vary. For example, spores are resistant to disinfectants because the spore coat and cortex act as a barrier,
mycobacteria have a waxy cell wall that prevents disinfectant entry, and gram-negative bacteria possess an outer membrane that acts as a barrier to the uptake of disinfectants (71, 72, 73 and 74). Implicit in all disinfection strategies is the consideration that the most resistant microbial subpopulation controls the sterilization or disinfection time. That is, in order to destroy the most resistant types of microorganisms-bacterial spores, the user needs to employ exposure times and a concentration of germicide needed to achieve complete destruction. With the exception of prions, bacterial spores possess the highest innate resistance to chemical germicides, followed by coccidia (e.g., Cryptosporidium), mycobacteria (e.g., M. tuberculosis), nonlipid or small viruses (e.g., poliovirus and coxsackievirus), fungi (e.g., Aspergillus and Candida), vegetative bacteria (e.g., Staphylococcus and Pseudomonas), and lipid or medium-size viruses (e.g., herpes, and HIV). The germicidal resistance exhibited by the gram-positive and gram-negative bacteria is similar with some exceptions (e.g., Pseudomonas aeruginosa, which shows greater resistance to some disinfectants) (75, 76 and 77). P. aeruginosa have also been shown to be significantly more resistant to a variety of disinfectants in their “naturally occurring” state as compared to cells subcultured on laboratory media (75,78). Rickettsiae, Chlamydiae, and mycoplasma cannot be placed in this scale of relative resistance because information on the efficacy of germicides against these agents is limited (79). Since these microorganisms contain lipid and are similar in structure and composition to other bacteria, it might be predicted that they would be inactivated by the same germicides that destroy lipid viruses and vegetative bacteria. A known exception to this supposition is Coxiella burnetii, which has demonstrated resistance to disinfectants (80).

FIGURE 80-1 Decreasing order of resistance of microorganisms to disinfection and sterilization and the level of disinfection or sterilization. (Data from Favero MS, Bond WW. Chemical disinfection of medical and surgical materials. In: Block SS, ed. Disinfection, sterilization, and preservation. Philadelphia, PA: Lippincott Williams & Wilkins, 2001:881-917; Russell AD. Bacterial resistance to disinfectants: present knowledge and future problems. J Hosp Infect 1998;43:S57-S68.)

Concentration and Potency of Disinfectants

With other variables constant, and with one exception (i.e., iodophors), the more concentrated the disinfectant, the greater its efficacy and the shorter the time necessary to achieve microbial kill. Generally not recognized, however, is that all disinfectants are not similarly affected by concentration adjustments. For example, quaternary ammonium compounds and phenol have a concentration exponent of 1 and 6, respectively; thus, halving the concentration of a quaternary ammonium compound requires a doubling of its disinfecting time, but halving the concentration of a phenol solution requires a 64-fold (i.e., 2⁶) increase in its disinfecting time (69,81,82).

Quality control is indispensable for automated disinfectant dilution systems. While these systems are economical, efficient and promote a safer workplace, compared to manual dilution methods, failure to provide the required concentration of the disinfectant has been reported. Disinfectants must be used in the dilution specified by the manufacturer for optimal decontamination and attention must be given to quality control and preventive maintenance of automated disinfectant dilution systems as they regularly fail (83).

It is also important to consider the length of the disinfection time, which is dependent upon the potency of the germicide. This was illustrated by Spaulding who demonstrated using the mucin-loop test that 70% isopropyl alcohol destroyed 104 M. tuberculosis in 5 minutes, whereas a simultaneous test with 3% phenolic required 2 to 3 hours to achieve the same level of microbial kill (19).

Physical and Chemical Factors

Several physical and chemical factors also influence disinfectant procedures: temperature, pH, relative humidity, and water hardness. For example, the activity of most disinfectants increases as the temperature increases, but there are exceptions. Further, too great an increase in temperature will cause the disinfectant to degrade, weaken its germicidal activity, and may produce a potential health hazard.

An increase in pH improves the antimicrobial activity of some disinfectants (e.g., glutaraldehyde, quaternary ammonium compounds) but decreases the antimicrobial activity of others (e.g., phenols, hypochlorites, and iodine). The pH influences the antimicrobial activity by altering the disinfectant molecule or the cell surface (69).

Relative humidity is the single most important factor influencing the activity of gaseous disinfectants/sterilants such as ETO, chlorine dioxide, and formaldehyde.

Water hardness (i.e., high concentration of divalent cations) reduces the rate of kill of certain disinfectants. This occurs because divalent cations (e.g., magnesium, calcium) in the hard water interact with the disinfectant to form insoluble precipitates (18,84).

Organic and Inorganic Matter

Organic matter in the form of serum, blood, pus, fecal, or lubricant material may interfere with the antimicrobial activity of disinfectants in at least two ways. Most commonly, the interference occurs by a chemical reaction between the germicide and the organic matter resulting in a complex that is less germicidal or nongermicidal, leaving less of the active germicide available for attacking microorganisms. Chlorine and iodine disinfectants, in particular, are prone to such interaction. Alternatively, organic material may protect microorganisms from attack by acting as a physical barrier (85).

The effects of inorganic contaminants on the sterilization process were studied in the 1950s and 1960s (86,87). These studies and other studies show the protection of microorganisms to all sterilization processes is due to
occlusion in salt crystals (88,89). This further emphasizes the importance of meticulous cleaning of medical devices before any sterilization or disinfection procedure since both organic and inorganic soils are easily removed by washing (88).

Duration of Exposure

Items must be exposed to the germicide for the appropriate minimum contact time. Multiple investigators have demonstrated the effectiveness of low-level disinfectants against vegetative bacteria (e.g., Listeria, Escherichia coli, Salmonella, vancomycin-resistant Enterococci [VRE], methicillin-resistant Staphylococcus aureus [MRSA]), yeasts (e.g., Candida), mycobacteria (e.g., M. tuberculosis), and viruses (e.g. poliovirus) at exposure times of 30 to 60 seconds (42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56 and 57,90, 91, 92, 93, 94 and 95). By 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 for any injuries resulting from off-label use and is potentially subject to enforcement action under FIFRA. While we are unaware of an EPA enforcement action against healthcare facilities for “off label” use of a surface disinfectant, there have been citations reported from The Joint Commission and the Center for Medicare and Medicaid Services (CMS).

All lumens and channels of endoscopic instruments must come in contact with the disinfectant. Air pockets will interfere with the disinfection process and items that float on the disinfectant will not be disinfected. The disinfectant must be introduced reliably into the internal channels of the device. The exact times for disinfecting medical items are somewhat elusive because of the effect of the aforementioned factors on disinfection efficacy. Contact times that have proved reliable are presented in Table 80-1, but, in general, the longer contact times are more effective than shorter ones.

Biofilms

Microorganisms may be protected from disinfectants due to the production of thick masses of cells (96) and extracellular materials or biofilms (97, 98, 99, 100, 101, 102, 103 and 104). Biofilms are microbial masses attached to surfaces that are immersed in liquids. Once these masses are formed, microbes may be resistant to the disinfectants by multiple mechanisms including higher resistance of older biofilms, genotypic variation of the bacteria, microbial production of neutralizing enzymes, and physiologic gradients within the biofilm (e.g., pH). Bacteria within biofilms are up to 1,000 times more resistant to antimicrobials than the same bacteria in suspension (105). Although new decontamination methods (106) are being investigated for removal of biofilms, chlorine and monochloramines are effective for inactivation of biofilm bacteria (99,107). Investigators have hypothesized that the glycocalyx-like cellular masses on the interior walls of polyvinyl chloride pipe would protect embedded microorganisms from some disinfectants and serve as a reservoir for continuous contamination (97,98,108). Biofilms have been found in whirlpools (109), dental unit waterlines (110), and numerous medical devices (e.g., contact lenses, pacemakers, hemodialysis systems, urinary catheters, central venous catheters, endoscopes) (102,105,107,111). Their presence may have serious implications for immunocompromised patients and patients with indwelling medical devices. Some enzymes (105,112,113) and detergents (105,114) can be used for the degradation of biofilms or reduction in viable bacterial numbers, but no products are registered by the EPA or cleared by the FDA for this purpose. One study evaluating the clearance effect of enzymatic and nonenzymatic detergents against E. coli biofilms on the inner surface of gastroscopes found that both nonenzymatic detergents and high-speed lavage (250 mL/min) are important in temporal formed biofilm elimination (115).

In general, the available data suggest that reusable medical devices (e.g., flexible endoscopes) that are properly cleaned, disinfected, rinsed, and dried pose little risk for biofilm development. However, biofilms can develop inside channels if established protocols are not met, and these biofilms can be difficult to remove (104).

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 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 washerdisinfector), 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 (116). When using a washerdisinfector, 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 (117). While ultrasound alone does not cause significant inactivation of bacteria, sonication can act synergistically to increase the cidal efficacy of a disinfectant (118). 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 (119). 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 (120,121). 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) (122). Washerdisinfectors 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 (123). Detailed information on cleaning and preparation of supplies for terminal sterilization is provided by professional organizations (124,125) and books (126). Studies have shown that manual and mechanical cleaning of endoscopes achieves approximately a 4-log₁₀ reduction of contaminating microorganisms (127, 128, 129 and 130). Thus, cleaning alone is very effective in reducing the number of microorganisms present on contaminated equipment. Quantitative analysis of residual protein contamination of reprocessed surgical instruments has been done, and median levels of residual protein contamination per instrument for five trays were 267, 260, 163, 456, and 756 µg (131). In another study, the median amount of protein from reprocessed surgical instruments from different hospitals ranged from 8 to 91 µg (132). 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 for cleaning biopsy forceps and ported and nonported laparoscopic devices and achieved a >99% reduction in soil parameters (i.e., protein, carbohydrate, hemoglobin) in the ported and nonported laparoscopic devices (133,134).

The best 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, residual amounts of high-level disinfectants, proteinaceous residue) could result (135,136). Enzyme solutions should be used in accordance with manufacturer’s instructions, which includes proper dilution of the enzymatic detergent for the amount of time specified on the label (136). 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 (129). Alkaline-based cleaning agents are used for processing medical devices as they dissolve protein and fat residues efficiently; (137) however, they may be corrosive (129). Some data demonstrate that enzymatic cleaners are more effective cleaners than neutral detergents (138,139) in removing microorganisms from surfaces, but two more recent studies found no difference in cleaning efficiency between enzymatic- and alkaline-based cleaners (112,137). 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 (140). In addition, this product was able to effect a 5-log₁₀ reduction in microbial loads with a 3-minute exposure at room temperature (140). 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 (141, 142, 143 and 144). The only way to ensure adequate cleaning is to conduct a reprocessing verification test (e.g., microbiologic sampling), but this is not routinely recommended (145). 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 (88,143). In the past few years, data have 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 (123,146, 147, 148, 149, 150 and 151) and adenosine triphosphate bioluminescence and microbiologic sampling to evaluate the effectiveness of cleaning (152). Minimally, all instruments should be individually inspected and be visibly clean.

DISINFECTANTS USED IN HEALTHCARE

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, orthophthalaldehyde, hydrogen peroxide, iodophors, peracetic acid, phenolics, and quaternary ammonium compounds. The properties of an ideal disinfectant are described in Table 80-2. With some exceptions (e.g., ethanol or bleach), commercial formulations based on these chemicals are considered unique products and must be registered with the 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. Additionally, caution must be exercised to avoid hazards with using cleaners and disinfectants on electronic medical equipment. Problems associated with inappropriate use of liquids on electronic medical equipment have included equipment fires, equipment malfunctions, and healthcare worker burns (153).

Disinfectants are not interchangeable and an overview of the performance characteristics of each is provided below, so the user has sufficient information to select an
appropriate disinfectant for any medical 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 and glutaraldehyde, and precautions (e.g., gloves, proper ventilation) should be used to minimize exposure (154). 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 Occupational Safety and Health Administration (OSHA) or recommended by NIOSH. The preferred method of control is to eliminate aerosolization of the chemical (via engineering controls, or substitution) or relocate the worker.

TABLE 80-2 Properties of an Ideal Disinfectant

Broad spectrum: should have a wide antimicrobial spectrum

Fast acting: should produce a rapid kill

Not affected by environmental factors: should be active in the presence of organic matter (e.g., blood, sputum, feces) and compatible with soaps, detergents, and other chemicals encountered in use

Nontoxic: should not be harmful to the user or patient

Surface compatibility: should not corrode instruments and metallic surfaces and should not cause the deterioration of cloth, rubber, plastics, and other materials

Residual effect on treated surfaces: should leave an antimicrobial film on the treated surface

Easy to use with clear label directions

Odorless: should have a pleasant odor or no odor to facilitate its routine use

Economical: should not be prohibitively high in cost

Solubility: should be soluble in water

Stability: should be stable in concentrate and use-dilution

Cleaner: should have good cleaning properties

Environmentally friendly: should not damage the environment on disposal

(Modified from Molinari JA, Gleason MJ, Cottone JA, Barrett ED. Comparison of dental surface disinfectants. Gen. Dent. 1987;35: 171-175.)

Chemical Disinfectants

Alcohol In the healthcare setting, “alcohol” refers to two water-soluble chemical compounds whose germicidal characteristics are generally underrated: ethyl alcohol and isopropyl alcohol (155). These alcohols are rapidly bactericidal rather than bacteriostatic against vegetative forms of bacteria; they also are tuberculocidal, fungicidal, and virucidal (enveloped viruses but poor activity against some nonenveloped viruses such as parvovirus) (156) but do not destroy bacterial spores. Their cidal activity drops sharply when diluted below 50% concentration and the optimum bactericidal concentration is in the range of 60-90% solutions in water (volume/volume) (157,158).

Alcohols are not recommended for sterilizing medical and surgical materials principally because of their lack of sporicidal action and their inability to penetrate proteinrich materials. Fatal postoperative wound infections with Clostridium have occurred when alcohols were used to sterilize surgical instruments contaminated with bacterial spores (159). Alcohols have been used effectively to disinfect oral and rectal thermometers, hospital pagers, scissors, CPR manikins, external surfaces of equipment (e.g., ventilator), computer keyboards (60), touch pads, and stethoscopes (12). Alcohol towelettes have been used for years to disinfect small surfaces such as rubber stoppers of multiple-dose medication vials or vaccine bottles.

Alcohols are flammable and consequently must be stored in a cool, well-ventilated area. They also evaporate rapidly and this makes extended exposure time difficult to achieve unless the items are immersed.

Chlorine and Chlorine Compounds Hypochlorites are the most widely used of the chlorine disinfectants and are available in a liquid (e.g., sodium hypochlorite) or solid (e.g., calcium hypochlorite) form. The most prevalent chlorine products in the United States are aqueous solutions of 5.25% to 6.15% sodium hypochlorite, which usually are called household bleach. A chlorine-containing product is currently registered by the EPA to kill C. difficile spores. They have a broad spectrum of antimicrobial activity (i.e., bactericidal, virucidal, fungicidal, mycobactericidal, sporicidal), do not leave toxic residues, are unaffected by water hardness, are inexpensive and fast acting (160), remove dried or fixed microorganisms and biofilms from surfaces (138), and have a low incidence of serious toxicity (161,162). Sodium hypochlorite at the concentration used in domestic bleach (5.25-6.15%) may produce ocular irritation or oropharygeal, esophageal, and gastric burns (154,163,164). Other disadvantages of hypochlorites include corrosiveness to metals in high concentrations (>500 ppm), inactivation by organic matter, discoloring or “bleaching” of fabrics, release of toxic chlorine gas when mixed with ammonia or acid (e.g., household cleaning agents) (165), and relative stability (166).

Reports have examined the microbicidal activity of a new disinfectant, “superoxidized water.” The concept of electrolyzing saline to create a disinfectant or antiseptics is appealing as the basic materials of saline and electricity are cheap and the end product (i.e., water) is not damaging to the environment. The main products of this water are hypochlorous acid (HOCl) and hypochlorite (OCl-), which constitute free available chlorine. This is also known as electrolyzed water and as with any germicide, the antimicrobial activity of superoxidized water is strongly affected by the concentration of the active ingredient (available free chlorine) (167). The free available chlorine concentrations of different superoxidized solutions reported in the literature range from 7 to 180 ppm (167). Data have shown that freshly generated superoxidized water, Sterilox®, is rapidly effective (<2 minutes) in achieving a 5-log₁₀ reduction of pathogenic microorganisms (i.e., M. tuberculosis, M. chelonae, poliovirus, HIV, MRSA, E. coli, Candida albicans, Enterococcus faecalis, Pseudomonas aeruginosa) in the absence of organic loading. However, the biocidal activity of this disinfectant was substantially reduced in the presence of organic material (5% horse serum) (168,169).

Hypochlorites are widely used in healthcare facilities in a variety of settings (160). Inorganic chlorine solution is used for disinfecting tonometer heads (170) and for spot disinfection of counter tops and floors. A 1:10 to 1:100 dilution of 5.25-6.15% sodium hypochlorite (i.e., household bleach) (171, 172, 173 and 174) or an EPA-registered tuberculocidal disinfectant (22) has been recommended for decontaminating blood spills. For small spills of blood (i.e., drops of blood) on noncritical surfaces, the area can be disinfected with a 1:100 dilution of 5.25-6.15% sodium hypochlorite or an EPA-registered tuberculocidal disinfectant. Because hypochlorites and other germicides are substantially inactivated in the presence of blood (54,175), large spills of blood require that the surface be cleaned before an EPA-registered disinfectant or a 1:10 (final concentration) solution of household bleach is applied. If there is a possibility of a sharps injury, there should be an initial decontamination (154,176), followed by cleaning and terminal disinfection (1:10 final concentration) (54). Extreme care should always be employed to prevent percutaneous injury. At least 500 ppm available chlorine for 10 minutes is recommended for decontamination of cardiopulmonary resuscitation training manikins. Other uses in healthcare include as an irrigating agent in endodontic treatment and for disinfecting laundry, dental appliances, hydrotherapy tanks (40), regulated medical waste before disposal (160), applanation tonometers, (177) and the water distribution system in hemodialysis centers and hemodialysis machines (12). Disinfection with a 1:10 dilution of concentrated sodium hypochlorite (i.e., bleach) has been shown to be effective in reducing environmental contamination in patient rooms and in reducing C. difficile infection rates in hospital units where there is a high endemic C. difficile infection rate or in an outbreak setting (11,178,179). Recently, Hacek and colleagues reported that the use of bleach (1:10 dilution) in the rooms of all patients with CDI at terminal room cleaning made a sustained, significant impact on reducing the rate of healthcare-associated CDI in a healthcare system (180).

Chlorine has long been favored as the preferred disinfectant in water treatment. Hyperchlorination of a Legionellacontaminated hospital water system (40) resulted in a dramatic decrease (30% to 1.5%) in the isolation of L. pneumophila from water outlets and a cessation of healthcare-associated Legionnaires’ disease in the affected unit (181,182). Chloramine T and hypochlorites have been used in disinfecting hydrotherapy equipment (12).

Hypochlorite solutions in tapwater at a pH >8 stored at room temperature (23°C) in closed, opaque plastic containers may lose up to 40-50% of their free available chlorine level over a period of 1 month. Thus, if a user wished to have a solution containing 500 ppm of available chlorine at day 30, a solution containing 1,000 ppm of chlorine should be prepared at time 0. There is no decomposition of sodium hypochlorite solution after 30 days when stored in a closed brown bottle (166).

Glutaraldehyde Glutaraldehyde is a saturated dialdehyde that has gained wide acceptance as a high-level disinfectant and chemical sterilant (183). Aqueous solutions of glutaraldehyde are acidic and generally in this state are not sporicidal. Only when the solution is “activated” (made alkaline) by use of alkalinizing agents to pH 7.5 to 8.5 does the solution become sporicidal. Once “activated,” these solutions have a shelf-life of minimally 14 days because of the polymerization of the glutaraldehyde molecules at alkaline pH levels. This polymerization blocks the active sites (aldehyde groups) of the glutaraldehyde molecules that are responsible for its biocidal activity.

Novel glutaraldehyde formulations (e.g., glutaraldehyde-phenol-sodium phenate, potentiated acid glutaraldehyde, stabilized alkaline glutaraldehyde) produced in the past 40 years have overcome the problem of rapid loss of activity (e.g., use- life: 28 to 30 days) while generally maintaining excellent microbicidal activity (12,184,185). However, it should be recognized that antimicrobial activity is dependent not only on age but also on use conditions such as dilution and organic stress. The use of glutaraldehydebased solutions in healthcare facilities is common because of their advantages that include excellent biocidal properties; activity in the presence of organic matter (20% bovine serum); and noncorrosive action to endoscopic equipment, thermometers, rubber, or plastic equipment. The advantages, disadvantages, and characteristics of glutaraldehyde are listed in Table 80-3.

The in vitro inactivation of microorganisms by glutaraldehydes has been extensively investigated and reviewed (186). Several investigators showed that >2% aqueous solutions of glutaraldehyde, buffered to pH 7.5 to 8.5 with sodium bicarbonate, were effective in killing vegetative bacteria in <2 minutes; M. tuberculosis, fungi, and viruses in <10 minutes; and spores of Bacillus and Clostridium species in 3 hours (186,187). Spores of Clostridium difficile are more rapidly killed by 2% glutaraldehyde than are spores of other species of Clostridium and Bacillus (188,189), this includes the hypervirulent binary toxin stains of C. difficile spores (WA Rutala, Unpublished Results, October 2009). There have been reports of microorganisms with relative resistance to glutaraldehyde, including some mycobacteria (Mycobacterium chelonae, M. avium-intracellulare, M. xenopi) (190,191), Methylobacterium mesophilicum (192), Trichosporon, fungal ascospores (e.g., Microascus cinereus, Cheatomium globosum), and Cryptosporidium (193). M. chelonae persisted in a 0.2% glutaraldehyde solution used to store porcine prosthetic heart valves (194) and a large outbreak of M. massiliense infections in Brazil after videolaparoscopy equipment, used for different elective cosmetic procedures (e.g., liposuction), was highly tolerant to 2% glutaraldehyde (195) Porins may have a role in the resistance of mycobacteria to glutaraldehyde and OPA (196).

Dilution of glutaraldehyde during use commonly occurs and studies show a glutaraldehyde concentration decline after a few days of use in an automatic endoscope washer (197). This occurs because instruments are not thoroughly dried and water is carried in with the instrument, which increases the solution’s volume and dilutes its effective concentration. This emphasizes the need to ensure that semicritical equipment is disinfected with an acceptable concentration of glutaraldehyde. Data suggest that 1.0% to 1.5% glutaraldehyde is the minimum effective concentration for >2% glutaraldehyde solutions when used as a highlevel disinfectant (197, 198 and 199). Chemical test strips or liquid chemical monitors are available for determining whether an effective concentration of glutaraldehyde is present despite repeated use and dilution. The frequency of testing should be based on how frequently the solutions are used (e.g., used daily, test daily; used weekly, test before

use; used 30 times per day, test each tenth use), but the strips should not be used to extend the use life beyond the expiration date. Data suggest the chemicals in the test strip deteriorate with time (200), and a manufacturer’s expiration date should be placed on the bottles. The bottle of test strips should be dated when opened and used for the period of time indicated on the bottle (e.g., 120 days). The results of test strip monitoring should be documented. The glutaraldehyde test kits have been preliminarily evaluated for accuracy and range (200), but the reliability has been questioned (201). The concentration should be considered unacceptable or unsafe when the test indicates a dilution below the product’s minimum effective concentration or MEC (generally to 1.0 to 1.5% glutaraldehyde or lower) by the indicator not changing color.

TABLE 80-3 Summary of Advantages and Disadvantages of Chemical Agents Used as Chemical Sterilants^a or as High-Level Disinfectants

*Sterilization Method*	*Advantages*	*Disadvantages*
Peracetic acid plus hydrogen peroxide	No activation required Odor or irritation not significant	Materials 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 materials compatibility	Respiratory irritation from glutaraldehyde vapor Pungent and irritating odor Relatively slow mycobactericidal activity Coagulates blood and fixes tissue to surfaces Allergic contact dermatitis Glutaraldehyde vapor monitoring recommended
Hydrogen peroxide	No activation required May enhance removal of organic matter and microorganisms 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 Does not require special venting or air monitoring	Stains skin, mucous membranes, clothing, and environmental surfaces Repeated exposure may result in hypersensitivity in some patients with bladder cancer More expensive than glutaraldehyde Eye irritation with contact Slow sporicidal activity
Peracetic acid	Rapid sterilization cycle time (30-45 min) Low-temperature (50-55°C) liquid immersion sterilization Environment-friendly byproducts (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 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, ureteroscopes) 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
Accelerated hydrogen peroxide (2.0%); high-level disinfectant	No activation required No odor Nonstaining No special venting requirements Manual or automated applications 12-mo shelf life, 14-d reuse 8 min at 20°C high-level disinfectant claim	Material compatibility concerns due to limited clinical experience Antimicrobial claims not independently verified Organic material resistance concerns due to limited data
^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). The above characteristics are documented in the literature; contact the manufacturer of the instrument and sterilant for additional information. All products listed above are FDA-cleared as chemical sterilants except OPA, which is an FDA-cleared high-level disinfectant. (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.)

Glutaraldehyde is used most commonly as a high-level disinfectant for medical equipment such as endoscopes (176), spirometry tubing, dialyzers, transducers, anesthesia and respiratory therapy equipment, hemodialysis proportioning and dialysate delivery systems, and reuse of laparoscopic disposable plastic trocars (12). Glutaraldehyde is noncorrosive to metal and does not damage lensed instruments, rubber or plastics. The FDA–cleared labels for highlevel disinfection with >2% glutaraldehyde at 25°C range from 20 to 90 minutes depending upon the product. However, multiple scientific studies and professional organizations support the efficacy of >2% glutaraldehyde for 20 minutes at 20°C (11,22,39). Minimally, follow this latter recommendation. Glutaraldehyde should not be used for cleaning noncritical surfaces as it is too toxic and expensive.

Chemical colitis (presents clinically with severe abdominal pain, bloody and mucoid diarrhea, rectal bleeding, and tenesmus 48-72 hours after colonoscopy) believed due to glutaraldehyde exposure from residual disinfecting solution in the endoscope solution channels has been reported and is preventable by careful endoscope rinsing (154). One study found that residual glutaraldehyde levels were higher and more variable after manual disinfection (<0.2-159.5 mg/L) than after automatic disinfection (0.2-6.3 mg/L) (202). Similarly, keratopathy and corneal decompensation were caused by ophthalmic instruments that were inadequately rinsed after soaking in 2% glutaraldehyde (203).

Glutaraldehyde exposure should be monitored to ensure a safe work environment. In the absence of an OSHA PEL, if the glutaraldehyde level is higher than the ACGIH ceiling limit of 0.05 ppm, it would be prudent to take corrective action and repeat monitoring (204).

Hydrogen Peroxide The literature contains several accounts of the properties, germicidal effectiveness, and potential uses for stabilized hydrogen peroxide in the healthcare setting. Published reports ascribing good germicidal activity to hydrogen peroxide have been published and attest to its bactericidal, virucidal, sporicidal, and fungicidal properties (205, 206, 207 and 208). The advantages, disadvantages, and characteristics of hydrogen peroxide are listed in Table 80-3. As with other chemical sterilants, dilution of the hydrogen peroxide must be monitored by regularly testing the minimum effective concentration (i.e., 7.5 to 6.0%). Compatibility testing by Olympus America of the 7.5% hydrogen peroxide found both cosmetic changes (e.g., discoloration of black anodized metal finishes) (176) and functional changes with the tested endoscopes (Olympus, October 15, 1999, written communication).

Commercially available 3% hydrogen peroxide is a stable and effective disinfectant when used on inanimate surfaces. It has been used in concentrations from 3 to 6% for the disinfection of soft contact lenses (e.g., 3% for 2-3 hours) (205,209), tonometer biprisms, ventilators, fabrics (210), and endoscopes (128). Hydrogen peroxide was effective in spot disinfecting fabrics in patients’ rooms (210). Corneal damage from a hydrogen peroxide-soaked tonometer tip that was not properly rinsed has been reported (211).

An accelerated hydrogen peroxide-based technology has been recently introduced into healthcare for disinfection of noncritical environmental surfaces and patient equipment (212), and high-level disinfection of semicritical equipment such as endoscopes (213). Accelerated hydrogen peroxide contains very low levels of anionic and nonionic surfactants that act with hydrogen peroxide to produce microbicidal activity. These ingredients are considered safe for humans and benign for the environment. It is prepared and marketed in several concentrations from 0.5% to 7%. The lower concentrations (0.5%) are designed for the disinfection of hard surfaces, while the higher concentrations (2%) are recommended for use as high-level disinfectants. A 0.5% accelerated hydrogen peroxide demonstrated bactericidal and virucidal activity in 1 minute and mycobactericidal and fungicidal activity in 5 minutes (212). It is more costly than other low-level disinfectants such as quaternary ammonium compounds. The product is claimed to have an excellent antimicrobial performance and a favorable safety profile. Another hydrogen peroxide-based technology has also been used for equipment cleaning (140).

As mentioned, a high-level disinfectant based on AHP (2.0%) is available for heat-sensitive semicritical medical devices including manual and automatic reprocessing of flexible endoscopes. It is odorless, nonstaining, ready to use, and has a 12-month shelf life and a 14-day reuse life. This product has demonstrated sporicidal activity, with a reduction in viability titer of >6-log₁₀ in 6 hours at 20°C, but also mycobactericidal, fungicidal, and virucidal activity with a contact time of 8 minutes. It is reported to be a relatively mild solution for end users and is considered to be compatible with flexible endoscopes. It is slightly irritating to skin and mildly irritating to eyes according to accepted standard test methods (same as 3% topical hydrogen peroxide) (213). AHP (7%) can be reused for several days and retain its broad-spectrum antimicrobial activity (214).

Iodophors Iodine solutions or tinctures have long been used by health professionals, primarily as antiseptics on skin or tissue. The FDA has not cleared any liquid chemical sterilant/high-level disinfectants with iodophors as the main active ingredient. However, iodophors have been used both as antiseptics and disinfectants. An iodophor is a combination of iodine and a solubilizing agent or carrier; the resulting complex provides a sustained-release reservoir of iodine and releases small amounts of free iodine in aqueous solution. The best known and most widely used iodophor is povidone-iodine, a compound of polyvinylpyrrolidone with iodine. This product and other iodophors retain the germicidal efficacy of iodine but, unlike iodine, are generally nonstaining and are relatively free of toxicity and irritancy (215).

There are several reports that documented intrinsic microbial contamination of antiseptic formulations of povidone-iodine and poloxamer-iodine (216,217). It was found that “free” iodine (I2) contributes to the bactericidal activity of iodophors, and dilutions of iodophors demonstrate more rapid bactericidal action than does a full-strength povidone-iodine solution. Therefore, iodophors must be diluted according to the manufacturers’ directions to achieve antimicrobial activity.

Published reports on the in vitro antimicrobial efficacy of iodophors demonstrate that iodophors are bactericidal, mycobactericidal, and virucidal but may require prolonged contact times to kill certain fungi and bacterial spores (19,218, 219, 220 and 221).

Besides their use as an antiseptic, iodophors have been used for the disinfection of blood culture bottles and medical equipment such as hydrotherapy tanks and thermometers. Antiseptic iodophors are not suitable for use as hard-surface disinfectants because of concentration differences. Iodophors formulated as antiseptics contain less free iodine than those formulated as disinfectants (222). Iodine or iodinebased antiseptics should not be used on silicone catheters as the silicone tubing may be adversely affected (223).

Ortho-phthalaldehyde (OPA) Ortho-phthalaldehyde is a high-level disinfectant that received FDA clearance in October 1999. It contains at least 0.55% OPA and it has supplanted glutaraldehyde as the most commonly used high-level disinfectant in the United States. OPA solution is a clear, pale-blue liquid with a pH of 7.5. The advantages, disadvantages, and characteristics of OPA are listed in Table 80-3.

Studies have demonstrated excellent microbicidal activity in in vitro studies (12,176,193,224, 225, 226, 227, 228 and 229) including superior mycobactericidal activity (5-log₁₀ reduction in 5 minutes) compared to glutaraldehyde. Walsh and colleagues also found OPA effective (>5-log₁₀ reduction) against a wide range of microorganisms, including glutaraldehyde-resistant mycobacteria and Bacillus atrophaeus spores (227).

OPA has several potential advantages compared to glutaraldehyde. It has excellent stability over a wide pH range (pH 3-9), is not a known irritant to the eyes and nasal passages, does not require exposure monitoring, has a barely perceptible odor, and requires no activation. OPA, like glutaraldehyde, has excellent material compatibility. A potential disadvantage of OPA is that it stains proteins gray (including unprotected skin) and thus must be handled with caution (176). However, skin staining would indicate improper handling that requires additional training and/or personal protective equipment (PPE) (gloves, eye and mouth protection, fluid-resistant gowns). OPA residues remaining on inadequately water-rinsed transesophageal echocardiogram probes may leave stains of the patient’s mouth. Meticulous cleaning, using the correct OPA exposure time (e.g., 12 minutes in the United States; 5 minutes at 25°C in an AER), and copious rinsing of the probe with water should eliminate this problem. Since OPA has been associated with several episodes of anaphylaxis following cystoscopy (230), the manufacturer has modified its instructions for use of OPA and contraindicates the use of OPA as a disinfectant for reprocessing all urological instrumentation for patients with a history of bladder cancer. PPE should be worn when handling contaminated instruments, equipment, and chemicals (225). In addition, equipment must be thoroughly rinsed to prevent discoloration of a patient’s skin or mucous membrane. The minimum effective concentration of OPA is 0.3% and that concentration is monitored by test strips designed specifically for the OPA solution. OPA exposure level monitoring found that the concentration during the disinfection process was significantly higher in the manual group (median: 1.43 ppb) than in the automatic group (median: 0.35 ppb). These findings corroborate other findings that show that it is desirable to introduce automatic endoscope reprocessors to decrease disinfectant exposure levels among scope reprocessing technicians (231).

Peracetic Acid Peracetic, or peroxyacetic acid, is characterized by a very rapid action against all microorganisms. Special advantages of peracetic acid are its lack of harmful decomposition products (i.e., acetic acid, water, oxygen, hydrogen peroxide), it enhances removal of organic material (232) and leaves no residue. It remains effective in the presence of organic matter and is sporicidal even at low temperatures. Peracetic acid can corrode copper, brass, bronze, plain steel, and galvanized iron, but these effects can be reduced by additives and pH modifications. The advantages, disadvantages, and characteristics of peracetic acid are listed in Table 80-3.

Peracetic acid will inactivate gram-positive and gramnegative bacteria, fungi, and yeasts in <5 minutes at <100 ppm. In the presence of organic matter, 200 to 500 ppm is required. For viruses, the dosage range is wide (12-2,250 ppm), with poliovirus inactivated in yeast extract in 15 minutes with 1,500 to 2,250 ppm. An automated machine using peracetic acid to reprocess heat-sensitive devices such as endoscopes and their accessories is used in the United States (233,234). In this system, a 35% concentration of peracetic acid is diluted to 0.2% with filtered water at a temperature of 50°C. Since the rinse water is tapwater that has been filtered and exposed to ultraviolet rays, it is not sterile. Therefore, the final processed devices are not sterile (FDA, April 6, 2010). Simulated-use trials have demonstrated excellent microbicidal activity (234, 235, 236, 237 and 238), and three clinical trials have demonstrated both excellent microbial killing and no clinical failures leading to infection (239, 240 and 241). Three clusters of infection using the peracetic acid automated endoscope reprocessor were linked to inadequately processed bronchoscopes when inappropriate channel connectors were used with the system (242,243). These clusters highlight the importance of training, proper model-specific endoscope connector systems, and quality control procedures to ensure compliance with endoscope manufacturer’s recommendations and professional organization guidelines. A high-level disinfectant available in the United Kingdom contains 0.35% peracetic acid. Although this product is rapidly effective against a broad range of microorganisms (244,245), it tarnishes the metal of endoscopes and is unstable, resulting in only a 24-hour use life (245).

Peracetic Acid with Hydrogen Peroxide Three chemical sterilants are FDA-cleared that contain peracetic acid plus hydrogen peroxide (0.08% peracetic acid plus 1.0% hydrogen peroxide, 0.23% peracetic acid plus 7.35% hydrogen peroxide, and 8.3% hydrogen peroxide plus 7.0% peracetic acid).
The advantages, disadvantages, and characteristics of peracetic acid with hydrogen peroxide are listed in Table 80-3.

The bactericidal properties of peracetic acid plus hydrogen peroxide have been demonstrated (246). Manufacturer’s data demonstrated that this combination of peracetic acid plus hydrogen peroxide inactivated all microorganisms with the exception of bacterial spores within 20 minutes. The 0.08% peracetic acid plus 1.0% hydrogen peroxide product was effective in inactivating a glutaraldehyde-resistant mycobacteria (247).

The combination of peracetic acid and hydrogen peroxide has been used for disinfecting hemodialyzers (248). The percentage of dialysis centers using a peracetic acid with hydrogen peroxide-based disinfectant for reprocessing dialyzers increased from 5% in 1983 to 62% in 2001 (249).

Phenolics Phenol has occupied a prominent place in the field of hospital disinfection since its initial use as a germicide by Lister in his pioneering work on antiseptic surgery. In the past 40 years, however, work has been concentrated upon the numerous phenol derivatives or phenolics and their antimicrobial properties. Phenol derivatives originate when a functional group (e.g., alkyl, phenyl, benzyl, halogen) replaces one of the hydrogen atoms on the aromatic ring. Two phenol derivatives commonly found as constituents of hospital disinfectants are ortho-phenylphenol and ortho-benzyl-para-chlorophenol.

Published reports on the antimicrobial efficacy of commonly used phenolics showed that they were bactericidal, fungicidal, virucidal, and tuberculocidal (12,19,53,76,218, 250, 251, 252 and 253).

Many phenolic germicides are EPA-registered as disinfectants for use on environmental surfaces (e.g., bedside tables, bedrails, laboratory surfaces) and noncritical medical devices. Phenolics are not FDA-cleared as highlevel disinfectants for use with semicritical items but could be used to preclean or decontaminate critical and semicritical devices prior to terminal sterilization or highlevel disinfection.

The use of phenolics in nurseries has been questioned because of the occurrence of hyperbilirubinemia in infants placed in bassinets where phenolic detergents were used (254). In addition, Doan and coworkers demonstrated bilirubin level increases in phenolic-exposed infants compared to nonphenolic-exposed infants when the phenolic was prepared according to the manufacturers’ recommended dilution (255). If phenolics are used to clean nursery floors, they must be diluted according to the recommendation on the product label. Phenolics (and other disinfectants) should not be used to clean infant bassinets and incubators while occupied. If phenolics are used to terminally clean infant bassinets and incubators, the surfaces should be rinsed thoroughly with water and dried before the infant bassinets and incubators are reused (22).

Quaternary Ammonium Compounds The quaternary ammonium compounds are widely used as surface disinfectants. There have been some reports of healthcare-associated infections associated with contaminated quaternary ammonium compounds used to disinfect patient-care supplies or equipment such as cystoscopes or cardiac catheters (256,257). As with several other disinfectants (e.g., phenolics, iodophors), gram-negative bacteria have been found to survive or grow in them (258).

Results from manufacturers’ data sheets and from published scientific literature indicate that the quaternaries sold as hospital disinfectants are generally fungicidal, bactericidal, and virucidal against lipophilic (enveloped) viruses; they are not sporicidal and generally not tuberculocidal or virucidal against hydrophilic (nonenveloped) viruses (19,49,50,52,53,92,218,259,260). Best et al. and Rutala et al. demonstrated the poor mycobactericidal activities of quaternary ammonium compounds (49,218).

The quaternaries are commonly used in ordinary environmental sanitation of noncritical surfaces such as floors, furniture, and walls. They have demonstrated sustained antimicrobial activity against VRE for 48 hours (59). EPA-registered quaternary ammonium compounds are appropriate to use when disinfecting medical equipment that come into contact with intact skin (e.g., blood pressure cuffs).

Pasteurization

Pasteurization is not a sterilization process; its purpose is to destroy all pathogenic microorganisms with the exception of bacterial spores. The time-temperature relation for hot-water pasteurization is generally >70°C (158°F) for 30 minutes. The water temperature and time should be monitored as part of a quality assurance program (261). Pasteurization of respiratory therapy (262,263) and anesthesia equipment (264) is a recognized alternative to chemical disinfection.

Ultraviolet Light

Ultraviolet light (UV) has been recognized as an effective method for killing microorganisms. It has been suggested for use in healthcare for several purposes to include air disinfection, room decontamination (see section Room Decontamination below), surface disinfection, biofilm disinfection (265), and ultrasound probe disinfection (266). Contaminated ultrasound probes can potentially transmit pathogens. When the probe is only in contact with the patient’s skin, there is a low risk of infection and low-level disinfection is recommended; however, a higher level of disinfection is recommended when the probe contacts mucous membranes or nonintact skin. An evaluation of a new disinfection procedure for ultrasound probes using ultraviolet light demonstrated the median microbial reduction for UV was 100%, 87.5% for antiseptic wiping, and 88% for dry wiping (266).

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Tags: Hospital Epidemiology and Infection Control

Jun 22, 2016 | Posted by drzezo in GENERAL & FAMILY MEDICINE | Comments Off

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