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Disinfection, Sterilization, and Control of Hospital Waste
Each year in the United States there are approximately 53,000,000 outpatient surgical procedures and 46,000,000 inpatient surgical procedures. For example, there are at least 18 million gastrointestinal endoscopies per year. Each of these procedures involves contact by a medical device or surgical instrument with a patient's sterile tissue and/or mucous membranes. A major risk of all such procedures is the introduction of infection. Failure to properly disinfect or sterilize medical devices and surgical instruments may lead to transmission via these devices (e.g., endoscopes contaminated with carbapenem-resistant Enterobacteriaceae [CRE]).
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, health care 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. Failure to comply with scientifically based guidelines has led to numerous outbreaks. In this chapter, which is an update of previous chapters, 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. In addition, we briefly review the management of medical waste in health care facilities.
Definition of Terms
Sterilization is defined as the complete elimination or destruction of all forms of microbial life and is accomplished in health care facilities through either physical or chemical processes. Steam under pressure, dry heat, ethylene oxide (ETO) gas, hydrogen peroxide gas plasma, vaporized hydrogen peroxide, hydrogen peroxide with ozone, and liquid chemicals are the principal sterilizing agents used in health care facilities. Sterilization is intended to convey an absolute meaning, not a relative one. Unfortunately, some health professionals and the technical and commercial literature refer to “disinfection” as “sterilization” and items as “partially sterile.” When chemicals are used for the purposes of destroying all forms of microbiologic 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 with 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 time of exposure to the germicide; the nature of the object (e.g., crevices, hinges, and lumens); the presence of biofilms; the temperature and pH during the disinfection process; and in some cases 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 (e.g., 3–12 hours) and are called chemical sterilants. At similar concentrations but with shorter exposure periods (e.g., 12 minutes for 0.55% ortho-phthalaldehyde [OPA]) 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 299.1 will be discussed later and consulted in this context.
TABLE 299.1
Methods for Disinfection and Sterilization of Patient Care Items and Environmental Surfaces
Modified from Rutala and Weber, Rutala and Weber, Rutala and Weber, Rutala and Weber, Rutala and Weber, Rutala and Weber, and Kohn et al.
| PROCESS | LEVEL OF MICROBIAL INACTIVATION | METHOD | EXAMPLES (WITH PROCESSING TIMES) | HEALTH CARE APPLICATION (EXAMPLES) |
|---|---|---|---|---|
| Sterilization a | Destroys all microorganisms, including bacterial spores | High temperature Low temperature Liquid immersion |
Steam (approximately 40 min), dry heat (1–6 h depending on temperature) Ethylene oxide gas (approximately 15 h), hydrogen peroxide gas plasma (24–60 min, 100 NX), hydrogen peroxide and ozone (46–60 min, VP4), hydrogen peroxide vapor (28–35 min, V-Pro MAX) Chemical sterilants b : >2% glut (approximately 10 h at 20°C–25°C); 1.12% glut with 1.93% phenol (12 h at 25°C); 7.35% HP with 0.23% PA (3 h at 20°C); 7.5% HP (6 h at 20°C); 1.0% HP with 0.08% PA (8 h at 20°C); approximately 0.2% PA (12 min at 50°C–56°C) |
Heat-tolerant critical (surgical instruments) and semicritical patient care items Heat-sensitive critical and semicritical patient care items Heat-sensitive critical and semicritical patient care items that can be immersed |
| High-level disinfection | Destroys all microorganisms except some bacterial spores | Heat automated Liquid immersion |
Pasteurization (65°C–77°C, 30 min) Chemical sterilants or high-level disinfectants b : >2% glut (20–90 min at 20°C–25°C); >2% glut (5 min at 35°C–37.8°C); 0.55% OPA (12 min at 20°C); 1.12% glut with 1.93% phenol (20 min at 25°C); 7.35% HP with 0.23% PA (15 min at 20°C); 7.5% HP (30 min at 20°C); 1.0% HP with 0.08% PA (25 min at 20°C); 650–675 free chlorine (10 min at 30°C); 2.0% HP (8 min at 20°C); 3.4% glut with 20.1% isopropanol (5 min at 25°C) |
Heat-sensitive semicritical items (e.g., respiratory therapy equipment) Heat-sensitive semicritical items (e.g., GI endoscopes, bronchoscopes, endocavitary probes) |
| Low-level disinfection | Destroys vegetative bacteria, some fungi and viruses, but not mycobacteria or spores | Liquid contact | EPA-registered hospital disinfectant with no tuberculocidal claim (e.g., chlorine-based products, phenolics, improved hydrogen peroxide, hydrogen peroxide plus peracetic acid, quaternary ammonium compounds [“quats”], quats plus alcohol—exposure times approximately 1 min) or 70–90% alcohol | Noncritical patient care item (blood pressure cuff) or surface (bedside table) with no visible blood |
EPA, US Environmental Protection Agency; FDA, US Food and Drug Administration; GI, gastrointestinal; glut, glutaraldehyde; HP, hydrogen peroxide; OPA, ortho-phthalaldehyde; PA, peracetic acid; ppm, parts per million.
a Prions (as in Creutzfeldt-Jakob disease) exhibit an unusual resistance to conventional chemical and physical decontamination methods and are not readily inactivated through conventional sterilization procedures.
b Consult the FDA cleared package insert for information about the cleared contact time and temperature, and see for discussion of why >2% glutaraldehyde products are used at a reduced exposure time (2% glutaraldehyde at 20 min, 20°C). Increasing the temperature through use of an automated endoscope reprocess (AER) will reduce the contact time (e.g., OPA 12 min at 20°C but 5 min at 25°C in AER). Exposure temperatures for some high-level disinfectants listed in the table varies from 20°C to 25°C; check FDA-cleared temperature conditions. Tubing must be completely filled for high-level disinfection and liquid chemical sterilization. Material compatibility should be investigated when appropriate (e.g., HP and HP with PA may cause functional damage to endoscopes). Intermediate-level disinfectants destroy vegetative bacteria, mycobacteria, most viruses, and most fungi but not spores and may include chlorine-based products, phenolics, and improved hydrogen peroxide). Intermediate-level disinfectants are not included in Table 299.1 because there is no device or surface for which intermediate-level disinfection is specifically recommended over low-level disinfection.
Cleaning , on the other hand, is the removal of visible soil (e.g., organic and inorganic material) and microbial contaminants 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 because inorganic and organic materials that remain on the surfaces of instruments interfere with the effectiveness of these processes. Also, if the soiled materials become dried or baked onto the instruments, the removal process becomes more difficult and the disinfection or sterilization process less effective or ineffective. Surgical instruments should be pretreated or rinsed to prevent drying of blood and to soften or remove blood from the instruments immediately or as soon as feasible after use. Treating contaminated instruments with alcohol, allowing instruments to soak in water for prolonged periods, or drying increases cleaning difficulty and should be discouraged. 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, whereas disinfectants are antimicrobials applied only to inanimate objects. Preservatives are agents that inhibit the growth of microorganisms capable of causing biologic deterioration of substances and materials. In general, antiseptics are used only 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.
Rational Approach to Disinfection and Sterilization
About 50 years ago, Earle H. Spaulding devised a rational approach to disinfection and sterilization of patient care items or equipment. This classification scheme is so clear and logical that it has been retained, refined, and successfully used by infection-control professionals and others when planning methods for disinfection or sterilization. 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. Although the scheme remains valid, there are some examples of disinfection studies with viruses, mycobacteria, and protozoa and of disinfectants that challenge the current definitions and expectations of high- and low-level disinfection. The three categories Spaulding 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. 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, arthroscopes, laparoscopes, and ultrasound probes used in sterile body cavities. Most of the items in this category should be purchased as sterile or be sterilized with steam sterilization if possible. If heat sensitive, the object may be treated with ETO, hydrogen peroxide gas plasma, vaporized hydrogen peroxide vapor, hydrogen peroxide vapor plus ozone, or liquid chemical sterilants if other methods are unsuitable. Tables 299.1, 299.2, and 299.3 summarize sterilization processes and liquid chemical sterilants and the advantages and disadvantages of each. Sterilization technologies can be relied on to produce sterility only if cleaning—to eliminate organic and inorganic material and microbial load—precedes treatment. Other issues that sterile reprocessing and operating room professionals must deal with when reprocessing instruments include weight limits for instrument trays, wet packs, packaging, loaned instruments, cleaning monitoring, and water quality.
TABLE 299.2
Summary of Advantages and Disadvantages of Chemical Agents Used as Chemical Sterilants or as High-Level Disinfectants a
Modified from Rutala and Weber, Rutala and Weber, Rutala and Weber, Rutala and Weber, Rutala and Weber, Rutala and Weber.
| STERILIZATION METHOD | ADVANTAGES | DISADVANTAGES |
|---|---|---|
| Peracetic acid and hydrogen peroxide | No activation required |
|
| Glutaraldehyde |
|
|
| Hydrogen peroxide (standard) |
|
|
| Ortho-phthalaldehyde (OPA) |
|
|
| Peracetic acid |
|
|
| Improved hydrogen peroxide (2.0%); high-level disinfectant |
|
|
AER, Automated endoscope reprocessor; FDA, US Food and Drug Administration.
a All products are effective in presence of organic soil, are relatively easy to use, and have a broad spectrum of antimicrobial activity (bacteria, fungi, viruses, bacterial spores, and mycobacteria). The listed characteristics are documented in the literature; contact the manufacturer of the instrument and high-level disinfectant or chemical sterilant for additional information. All products listed here are FDA cleared as chemical sterilants except OPA, which is an FDA-cleared high-level disinfectant.
TABLE 299.3
Summary of Advantages and Disadvantages of Commonly Used Sterilization Methods
Modified from Rutala and Weber, Rutala and Weber, Rutala and Weber, Rutala and Weber, Rutala and Weber, Rutala and Weber.
| STERILIZATION METHOD | ADVANTAGES | DISADVANTAGES |
|---|---|---|
| Steam |
|
|
| Hydrogen peroxide gas plasma |
|
|
| 100% Ethylene oxide (ETO) |
|
|
| Vaporized hydrogen peroxide |
|
|
| Hydrogen peroxide and ozone |
|
|
FDA, US Food and Drug Administration; TWA, time-weighted average.
Semicritical Items
Semicritical items are those that come in contact with intact mucous membranes or nonintact skin. Respiratory therapy and anesthesia equipment, some endoscopes, laryngoscope blades and handles, esophageal manometry probes, endocavitary probes, nasopharyngoscopes, prostate biopsy probes, infrared coagulation devices, anorectal manometry catheters, cystoscopes, 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 organisms such as bacteria, mycobacteria, and viruses. Semicritical items minimally require high-level disinfection with chemical disinfectants. Glutaraldehyde, hydrogen peroxide, OPA, peracetic acid, hypochorite (via superoxidized water) and peracetic acid with hydrogen peroxide are cleared by the Food and Drug Administration (FDA) and are dependable high-level disinfectants, provided that the factors influencing germicidal procedures are met (see Tables 299.1 and 299.2 ). 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. The FDA's definition of high-level disinfection is a sterilant used for a shorter contact time to achieve at least a 6-log 10 kill of an appropriate Mycobacterium species. Cleaning followed by high-level disinfection should eliminate all pathogens capable of causing infection.
Ideally, semicritical items should be rinsed with sterile water after high-level disinfection to prevent their contamination with organisms that may be present in tap water, such as nontuberculous mycobacteria, Legionella, or gram-negative bacilli such as Pseudomonas. In circumstances in which rinsing with sterile water rinse is not feasible, a tap water or filtered water (0.2-µ filter) rinse should be followed by an alcohol rinse and forced-air drying. Forced-air drying markedly reduces bacterial contamination of stored endoscopes, most likely by removing the wet environment favorable for bacterial growth. After rinsing, items should be dried and stored (e.g., packaged or hung) 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, ultrasound probes on intact skin [includes central line puncture site]) are usually considered noncritical surfaces and are disinfected with low or intermediate-level disinfectants. Because hydrotherapy tanks have been associated with spread of infection, some facilities have chosen to disinfect them with recommended levels of chlorine.
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, toys, portable equipment (e.g., wheelchairs, infusion pumps, pulse oximeters, medication carts), and floors. The five most commonly touched noncritical items in the patient environment have been quantitatively shown to be bed rails, bed surface, supply cart, overbed table, and intravenous pump. 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 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 health care providers or by contact with medical equipment that will subsequently come in contact with patients. Table 299.4 lists several low-level disinfectants that may be used for noncritical items. Many Environmental Protection Agency (EPA)–registered liquid 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 30 to 60 seconds. Accordingly, 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 approximately 1 minute. Because the typical drying time for a liquid disinfectant on a surface is 1 to 2 minutes (unless the product contains alcohol [e.g., a 60%–70% alcohol product will dry in about 30 seconds]), one application of the germicide on all hand contact or touchable surfaces to be disinfected is recommended.
TABLE 299.4
Summary of Advantages and Disadvantages of Disinfectants Used as Low-Level Disinfectants
Modified from Rutala and Weber, Rutala and Weber.
| DISINFECTANT ACTIVE | ADVANTAGES | DISADVANTAGES |
|---|---|---|
| Alcohol |
|
|
| Sodium hypochlorite |
|
|
| Improved hydrogen peroxide |
|
|
| Iodophors |
|
|
| Phenolics |
|
|
| Quaternary ammonium compounds a (e.g., didecyl dimethyl ammonium bromide, dioctyl dimethyl ammonium bromide) |
|
|
| Peracetic acid and hydrogen peroxide |
|
|
EPA, Environmental Protection Agency; HIV, human immunodeficiency virus.
a If low-level disinfectant is prepared on-site (not ready-to-use product), document correct concentration at a routine frequency.
Mops (microfiber and cotton-string), reusable cleaning cloths, disposable wipes, and sprays are regularly used to achieve low-level disinfection. Disinfectant cleaning wipes and sprays (e.g., quaternary ammonium compounds [“quats”] and alcohol, chlorine) have been found to be highly effective (>4-log 10 reduction) in removing or inactivating epidemiologically important pathogens. Hospital laundering practices may not be sufficient to remove microbial contaminants of reusable cleaning towels. 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 when compared with the detergent cleaner (95% vs. 68%, respectively). 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 health care facility. In one study, standard laundering provided acceptable decontamination of heavily contaminated mopheads, but chemical disinfection with a phenolic was less effective. 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. Three other methods have been offered for monitoring patient room hygiene: adenosine triphosphate (ATP) bioluminescence ; fluorescent markers ; and microbiologic sampling. Studies have demonstrated suboptimal cleaning through use of aerobic colony counts, ATP bioluminescence, and fluorescent markers. ATP bioluminescence and fluorescent markers are preferred to aerobic plate counts because they provide an immediate assessment of cleaning effectiveness. When the four major hospital cleaning validation methods (i.e., visual, microbiologic, ATP, and fluorescence) were compared, the fluorescent marker was the most useful tool in determining how thoroughly a surface was cleaned, and mimicked the microbiologic data better than ATP (<500 relative light units). There was no statistical correlation between ATP levels and standard aerobic plate counts.
Disinfection of Health Care Equipment and Surfaces
Disinfectants are used alone or in combinations in the health care setting. These include alcohols, chlorine and chlorine compounds, formaldehyde, glutaraldehyde, OPA, standard and improved (or accelerated) hydrogen peroxide, hydrogen peroxide plus peracetic acid, iodophors, peracetic acid, phenolics, quats, and quats and alcohol. Key considerations for selecting the optimal disinfectant include kill claims; treatment time or contact time; safety; and ease of use. 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. In addition, caution must be exercised to avoid hazards with use of 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 health care worker burns.
Disinfectants are not interchangeable, and an overview of the performance characteristics of each is provided in the following sections 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 and infection risks 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, and chlorine, and precautions (e.g., gloves, proper ventilation) should be used to minimize exposure. 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 Occupational Health and Safety Administration (OSHA) or recommended by the National Institute for Occupational Safety and Health (NIOSH). The preferred method of control is to eliminate the chemical (by means of engineering controls or substitution) or relocate the worker.
Chemical Disinfectants
Alcohol
In the health care setting, “alcohol” refers to two water-soluble chemical compounds whose germicidal characteristics are generally underrated: ethyl alcohol and isopropyl alcohol. These alcohols are rapidly bactericidal rather than bacteriostatic against vegetative forms of bacteria; they also are tuberculocidal, fungicidal, and virucidal 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% to 90% solutions in water (volume/volume).
Alcohols are not recommended for sterilizing medical and surgical materials, principally because of their lack of sporicidal action and their inability to penetrate protein-rich materials. Fatal postoperative wound infections with Clostridium have occurred when alcohols were used to sterilize surgical instruments contaminated with bacterial spores. Alcohols have been used effectively to disinfect oral and rectal thermometers, computers, hospital pagers, scissors, cardiopulmonary resuscitation (CPR) manikins, applanation tonometers, external surfaces of equipment (e.g., ventilators), and stethoscopes. 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. Large volumes of alcohol products need to be stored in rooms meeting special fire department regulations. 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. 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, remove dried or fixed organisms and biofilms from surfaces, and have a low incidence of serious toxicity. Sodium hypochlorite at the concentration used in domestic bleach (5.25%–6.15%) may produce ocular irritation or oropharyngeal, esophageal, and gastric burns, but the frequency is rare. Other disadvantages of hypochlorites include corrosiveness to metals at 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), and relative stability.
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 because the basic materials of saline and electricity are inexpensive and the end product (i.e., water) is not damaging to the environment. The main products of this water are hypochlorous acid (e.g., at a concentration of about 144 mg/L) and 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). The free available chlorine concentrations of different superoxidized solutions reported in the literature range from 7 to 180 ppm. Data have shown that freshly generated superoxidized water is rapidly effective (<2 minutes) in achieving a 5-log 10 reduction of pathogenic microorganisms (i.e., M. tuberculosis, Mycobacterium chelonae, poliovirus, human immunodeficiency virus [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).
Hypochlorites are widely used in health care facilities in a variety of settings. Inorganic chlorine solution is used for disinfecting tonometer heads and for disinfection of noncritical surfaces and equipment. A 1 : 10 to 1 : 100 dilution of 5.25% to 6.15% sodium hypochlorite (i.e., household bleach) or an EPA-registered tuberculocidal disinfectant 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% to 6.15% sodium hypochlorite or an EPA-registered tuberculocidal disinfectant. Because hypochlorites and other germicides are substantially inactivated in the presence of blood, 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, followed by cleaning and terminal disinfection (1 : 10 final concentration). Extreme care should always be employed to prevent percutaneous injury. At least 500 ppm available chlorine for 10 minutes is recommended for decontamination of CPR training manikins. Other uses in health care include as an irrigating agent in endodontic treatment and for disinfecting laundry, dental appliances, hydrotherapy tanks, regulated medical waste before disposal, applanation tonometers, and the water distribution system in hemodialysis centers and hemodialysis machines. 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 Clostridioides difficile (formerly Clostridium difficile ) infection rates in hospital units where there is a high endemic C. difficile infection rate or in an outbreak setting. At the University of North Carolina (UNC) Hospitals, we use a sporicidal solution (1 : 10 dilution of household bleach or approximately 5000 ppm chlorine) in all C. difficile– infected patient rooms for routine daily and terminal cleaning. This is done by means of one application of the sporicide, covering all hand contact surfaces to allow sufficient wetness for an approximately 1-minute contact time.
Chlorine has long been favored as the preferred disinfectant in water treatment. Hyperchlorination of a Legionella -contaminated hospital water system resulted in a dramatic decrease (30% to 1.5%) in the isolation of Legionella pneumophila from water outlets and a cessation of health care–associated legionnaires’ disease in the affected unit. Chloramine T and hypochlorites have been used in disinfecting hydrotherapy equipment.
Hypochlorite solutions in tap water at a pH greater than 8 stored at room temperature (20°C) in closed, opaque plastic containers may lose up to 40% to 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 1000 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.
Glutaraldehyde
Glutaraldehyde is a saturated dialdehyde that has gained wide acceptance as a high-level disinfectant and chemical sterilant. 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 50 years have overcome the problem of rapid loss of activity (e.g., current use life, 28–30 days) while generally maintaining excellent microbicidal activity. 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 glutaraldehyde-based solutions in health care facilities is common because of their advantages, including excellent biocidal properties; activity in the presence of organic matter (20% bovine serum); and noncorrosive action when used on endoscopic equipment, thermometers, or rubber or plastic equipment. The advantages, disadvantages, and characteristics of glutaraldehyde are listed in Table 299.2 .
The in vitro inactivation of microorganisms by glutaraldehydes has been extensively investigated and reviewed. 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. Spores of Clostridioides difficile are more rapidly killed by 2% glutaraldehyde than are spores of species of Clostridium and Bacillus ; this includes the hypervirulent binary toxin strains of C. difficile spores (WA Rutala, unpublished data, 2017). There have been reports of microorganisms with relative resistance to glutaraldehyde, including some mycobacteria ( M. chelonae, Mycobacterium avium-intracellulare, Mycobacterium xenopi ), Methylobacterium mesophilicum, Trichosporon, fungal ascospores (e.g., Microascus cinereus , Chaetomium globosum ), and Cryptosporidium. M. chelonae persisted in a 0.2% glutaraldehyde solution used to store porcine prosthetic heart valves. In a large outbreak of Mycobacterium massiliense infections in Brazil after videolaparoscopic equipment was used for different elective cosmetic procedures (e.g., liposuction), the organism was highly tolerant to 2% glutaraldehyde. Porins may have a role in the resistance of mycobacteria to glutaraldehyde and OPA.
Dilution of glutaraldehyde during use commonly occurs, and studies have shown a glutaraldehyde concentration decline after a few days of use in an automatic endoscope washer. 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 (MEC) for >2% glutaraldehyde solutions when used as a high-level disinfectant. 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), or the manufacturer's recommendation should be followed. The strips should not be used to extend the use life beyond the expiration date. Data suggest that the chemicals in the test strip deteriorate with time, 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, but the reliability has been questioned. The concentration should be considered unacceptable or unsafe when the test indicates a dilution below the product's MEC (generally to 1.0%–1.5% glutaraldehyde or lower) by the indicator not changing color.
Glutaraldehyde is used most commonly as a high-level disinfectant for medical equipment such as endoscopes, endocavitary probes, spirometry tubing, dialyzers, transducers, anesthesia and respiratory therapy equipment, hemodialysis proportioning, and dialysate delivery systems. Glutaraldehyde is noncorrosive to metal and does not damage lensed instruments, rubber, or plastics. The FDA - cleared labels for high-level disinfection with >2% glutaraldehyde at 20°C to 25°C range from 20 to 90 minutes depending on the product. However, multiple scientific studies and professional organizations support the efficacy of >2% glutaraldehyde for 20 minutes at 20°C. Minimally, one should follow this latter recommendation. Glutaraldehyde should not be used for cleaning noncritical surfaces, because it is too toxic and expensive.
Colitis believed to be due to glutaraldehyde exposure from residual disinfecting solution in the endoscope solution channels has been reported and is preventable through careful endoscope rinsing. 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). Similarly, keratopathy and corneal decompensation were caused by ophthalmic instruments that were inadequately rinsed after soaking in 2% glutaraldehyde.
Glutaraldehyde exposure should be monitored to ensure a safe work environment. In the absence of an OSHA permissible exposure limit (PEL), if the glutaraldehyde level is higher than the American Conference of Governmental Industrial Hygienists (ACGIH) ceiling limit of 0.05 ppm, it would be prudent to take corrective action and repeat monitoring.
Hydrogen Peroxide
The literature contains several accounts of the properties, germicidal effectiveness, and potential uses for stabilized hydrogen peroxide in the health care setting. Reports ascribing good germicidal activity to hydrogen peroxide have been published and attest to its bactericidal, virucidal, sporicidal, and fungicidal properties. Some other studies have shown limited bactericidal and virucidal activity of standard 3% hydrogen peroxide. The advantages, disadvantages, and characteristics of hydrogen peroxide are listed in Tables 299.2 and 299.4 . As with other chemical sterilants, dilution of the hydrogen peroxide must be monitored through regular testing of the MEC (i.e., 7.5%–6.0%). Compatibility testing by Olympus America of 7.5% hydrogen peroxide found both cosmetic changes (e.g., discoloration of black anodized metal finishes) and functional changes with the tested endoscopes (Olympus, written communication, October 15, 1999).
Commercially available 3% hydrogen peroxide is a stable and effective disinfectant when used on some 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), tonometer biprisms, ventilators, fabrics, and endoscopes. Hydrogen peroxide was effective in spot-disinfecting fabrics in patients’ rooms. Corneal damage from a hydrogen peroxide–soaked tonometer tip that was not properly rinsed has been reported.
Improved Hydrogen Peroxide
An improved hydrogen peroxide–based technology has been introduced into health care for disinfection of noncritical environmental surfaces and patient equipment and high-level disinfection of semicritical equipment such as endoscopes. Improved hydrogen peroxide contains very low levels of anionic and/or nonionic surfactants in an acidic product that act with hydrogen peroxide to produce microbicidal activity. This combination of ingredients speeds the antimicrobial activity of hydrogen peroxide and cleaning efficiency. Improved hydrogen peroxide is considered safe for humans and equipment, and benign for the environment. Improved hydrogen peroxide has the lowest EPA toxicity category (i.e., category IV) based on its oral, inhalation, and dermal toxicity, which means it is practically nontoxic and not an irritant. It is prepared and marketed by several companies in various concentrations (e.g., 0.5%–2%), and different companies may use different terminology for these products, such as “accelerated” or “activated.” Lower concentrations (i.e., 0.5%, 1.4%) are designed for the low-level disinfection of noncritical environmental surfaces and patient care objects; higher concentrations (i.e., 2.0%) can be used as high-level disinfectants for semicritical medical devices (e.g., endoscopes).
When a study compared the bactericidal activity of two improved hydrogen peroxide products versus standard 0.5%, 1.4%, and 3% hydrogen peroxide formulations, the improved hydrogen peroxide–based environmental surface disinfectants proved to be more effective (>6-log 10 reduction) and fast-acting (30–60 seconds) microbicides in the presence of a soil load (to simulate the presence of body fluids) than commercially available hydrogen peroxide. Only 30- to 60-second contact times were studied because longer contact times (e.g., 10 minutes) are not achievable in clinical practice. In 2017, Boyce and colleagues compared a quat disinfectant and an improved hydrogen peroxide and found the improved hydrogen peroxide reduced surface contamination and reduced a composite colonization or infection outcome. Another study demonstrated that 1.4% activated hydrogen peroxide is very effective in reducing microbial contamination of hospital privacy curtains. In fact, the activated hydrogen peroxide completely eliminated contamination with MRSA and VRE and resulted in a 98.5% reduction in microbes (only Bacillus sp. was recoverable). Thus, at UNC Hospitals, privacy curtains are being disinfected at the grab area by means of spraying the grab area of the curtain three times with activated hydrogen peroxide at discharge cleaning.
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 or high-level disinfectant with iodophors as the main active ingredient. However, iodophors have been used both as antiseptics and as 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.
There are several reports that document intrinsic microbial contamination of antiseptic formulations of povidone-iodine and poloxamer-iodine. It was found that “free” iodine (I 2 ) contributes to the bactericidal activity of iodophors and that 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 in order 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.
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.
Ortho-phthalaldehyde
OPA is a high-level disinfectant that received FDA clearance in October 1999. The solution contains at least 0.55% 1,2-benzenedicarboxaldehyde or OPA, and it has supplanted glutaraldehyde as the most commonly used “aldehyde” for high-level disinfection 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 299.2 .
In vitro studies have demonstrated excellent microbicidal activity, including superior mycobactericidal activity (5-log 10 reduction in 5 minutes) compared with glutaraldehyde. Walsh and colleagues also found OPA effective (>5-log 10 reduction) against a wide range of microorganisms, including glutaraldehyde-resistant mycobacteria and Bacillus atrophaeus spores.
OPA has several potential advantages compared with 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. However, skin staining would indicate improper handling and indicates a need for additional training and/or personal protective equipment (PPE) (gloves, eye and mouth protection, fluid-resistant gowns). OPA residues remaining on inadequately water-rinsed transesophageal echocardiography probes may leave stains on the patient's mouth. Meticulous cleaning, use of the correct OPA exposure time (e.g., 12 minutes), and copious rinsing of the probe with water should eliminate this problem. Because OPA has been associated with several episodes of anaphylaxis after cystoscopy, the manufacturer has modified its instructions for use of OPA and contraindicates the use of OPA as a disinfectant for reprocessing all urologic instruments for patients with a history of bladder cancer. PPE should be worn for handling of contaminated instruments, equipment, and chemicals. In addition, equipment must be thoroughly rinsed to prevent discoloration of a patient's skin or mucous membrane. The MEC of OPA is 0.3%, and that concentration is monitored with test strips designed specifically for the OPA solution. Monitoring of OPA exposure level revealed 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.
Peracetic Acid
Peracetic, or peroxyacetic acid, is characterized by a very rapid action against all microorganisms. Special advantages of peracetic acid include its lack of harmful decomposition products (i.e., acetic acid, water, oxygen, hydrogen peroxide); it enhances removal of organic material 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 with additives and pH modifications. The advantages, disadvantages, and characteristics of peracetic acid are listed in Table 299.2 .
Peracetic acid will inactivate gram-positive and gram-negative bacteria, fungi, and yeasts in less than 5 minutes at less than 100 ppm. In the presence of organic matter, 200 to 500 ppm is required. For viruses the dosage range is wide (12–2250 ppm), with poliovirus inactivated in yeast extract in 15 minutes with 1500 to 2250 ppm. A processing system using peracetic acid at a temperature of 50°C to 56°C can be used for processing heat-sensitive semicritical and critical devices that are compatible with the peracetic acid and processing system and that cannot be sterilized by other legally marketed traditional sterilization methods validated for that type of device (e.g., steam, hydrogen peroxide gas plasma, vaporized hydrogen peroxide). After processing, the devices should be used immediately or stored in a manner similar to that of a high-level disinfected endoscope. The sterilant, 35% peracetic acid, is diluted to 0.2% with tap water that has been filtered and exposed to ultraviolet (UV) light. Some data demonstrate the effectiveness of the liquid chemical sterilant processing system for reprocessing duodenoscopes. Simulated-use trials with the earlier version of this processing system have demonstrated excellent microbicidal activity, and three clinical trials have demonstrated both excellent microbial killing and no clinical failures leading to infection. Three clusters of infection with use of the earlier version of the peracetic acid automated endoscope reprocessor were linked to inadequately processed bronchoscopes when inappropriate channel connectors were used with the system. 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. An alternative 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, it tarnishes the metal of endoscopes and is unstable, resulting in only a 24-hour use life.
Peracetic Acid With Hydrogen Peroxide
Three chemical sterilants that contain peracetic acid plus hydrogen peroxide (e.g., 0.08% peracetic acid plus 1.0% hydrogen peroxide, 0.23% peracetic acid plus 7.35% hydrogen peroxide) have been cleared by the FDA. The advantages, disadvantages, and characteristics of peracetic acid with hydrogen peroxide are listed in Table 299.2 .
The bactericidal and sporicidal properties of peracetic acid plus hydrogen peroxide have been demonstrated. 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 Mycobacterium.
The combination of peracetic acid and hydrogen peroxide has been used for disinfecting hemodialyzers and environmental surfaces. This disinfectant product was associated with mucous membrane and respiratory health effects when used by hospital staff for surface disinfection. A study used a peracetic acid and hydrogen peroxide solution for all daily, discharge, and common area cleaning and found a significant decrease in hospital-onset C. difficile rates. The percentage of dialysis centers using a peracetic acid with hydrogen peroxide–based disinfectant for reprocessing dialyzers increased from 5% in 1983 to 72% in 1997.
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