Which sterilization method is the one most widely used in the medical office?

Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 2015 : 3294–3309.e4.

Guest Editor [s]: John E. Bennett, MD, MACP

Adjunct Professor of Medicine, Uniformed Services University of the Health Sciences, F. Edward Hebert School of Medicine, Bethesda, Maryland

Guest Editor [s]: Raphael Dolin, MD

Maxwell Finland Professor of Medicine [Microbiology and Molecular Genetics], Harvard Medical School, Boston, Massachusetts

Attending Physician, Beth Israel Deaconess Medical Center, Boston, Massachusetts

Brigham and Women' s Hospital, Boston, Massachusetts

Guest Editor [s]: Martin J. Blaser, MD

Muriel G. and George W. Singer Professor of Translational Medicine, Professor of Microbiology, Director, Human Microbiome Program, Departments of Medicine and Microbiology, New York University School of Medicine, Langone Medical Center, New York, New York

Each year in the United States there are approximately 53 million outpatient surgical procedures and 46 million inpatient surgical procedures.1 For example, there are at least 10 million gastrointestinal endoscopies per year.2 Each of these procedures involves contact by a medical device or surgical instrument with a patient's sterile tissue or mucous membranes. A major risk of all such procedures is the introduction of 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 for person-to-person transmission [e.g., hepatitis B virus] and transmission of environmental pathogens [e.g., Clostridium difficile].

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 item's intended use.

Multiple studies in many countries have documented lack of compliance with established guidelines for disinfection and sterilization.3, 4 Failure to comply with scientifically based guidelines has led to numerous outbreaks of infectious diseases.2, 4, 5, 6, 7, 8 In this chapter, which is an update of previous chapters,9, 10, 11, 12, 13 a pragmatic approach to the judicious selection and proper use of disinfection and sterilization processes is presented, based on well-designed studies assessing the efficacy [via laboratory investigations] and effectiveness [via clinical studies] of disinfection and sterilization procedures. In addition, we briefly review the management of medical waste in health care facilities.

Definition of Terms

Sterilization is the complete elimination or destruction of all forms of microbial life and is accomplished in health care facilities by either physical or chemical processes. Steam under pressure, dry heat, ethylene oxide [ETO] gas, hydrogen peroxide gas plasma, vaporized hydrogen peroxide, 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 care 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 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 by the use of liquid chemicals or wet pasteurization in health care settings. The efficacy of disinfection is affected by a number of factors, each of which may nullify or limit the efficacy of the process. Some of the factors that affect both disinfection and sterilization efficacy are the prior cleaning of the object; the organic and inorganic load present; the type and level of microbial contamination; the concentration of and exposure time to the germicide; the nature of the object [e.g., crevices, hinges, and lumens]; the presence of biofilms; the temperature and pH of the disinfection process; and, in some 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 to 12 hours] and are called chemical sterilants. At similar concentrations but with shorter exposure periods [e.g., 12 minutes for 0.55% ortho-phthalaldehyde] 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.

Cleaning, on the other hand, is the removal of visible soil [e.g., organic and inorganic material] from objects and surfaces, and it normally is accomplished by manual or mechanical means using water with detergents or enzymatic products. Thorough cleaning is essential before high-level disinfection and sterilization because inorganic and organic materials that remain on the surfaces of instruments interfere with the effectiveness of these processes. Also, if the soiled materials become dried or baked onto the instruments, the removal process becomes more difficult and the disinfection or sterilization process less effective or ineffective. Surgical instruments should be presoaked or rinsed to prevent drying of blood and to soften or remove blood from the instruments. 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 antimicrobial agents applied only to inanimate objects. Preservatives are agents that inhibit the growth of microorganisms capable of causing biologic deterioration of substances/materials. 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.14, 15, 16, 17, 18, 19

Rational Approach to Disinfection and Sterilization

About 45 years ago, Earle H. Spaulding15 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 for infection involved in the use of the items. Although the scheme remains valid, some examples of disinfection studies with viruses, mycobacteria, and protozoa challenge the current definitions and expectations of high- and low-level disinfection.22 The three categories Spaulding described were critical, semicritical, and noncritical.

Critical Items

Critical items are so called because of the high risk for 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, arthroscopes, laparoscopes, and ultrasound probes used in sterile body cavities. Most of the items in this category should be purchased in sterile form or be sterilized by steam sterilization if possible. If heat sensitive, the object may be treated with ETO, hydrogen peroxide gas plasma, hydrogen peroxide vapor, or liquid chemical sterilants if other methods are unsuitable. Tables 301-1 and 301-2 list several germicides categorized as chemical sterilants and high-level disinfectants. These include 2.4% or greater glutaraldehyde-based formulations, hypochlorous acid/hypochlorite 650 to 675 ppm free chlorine, 1.12% glutaraldehyde with 1.93% phenol/phenate, 3.4% glutaraldehyde with 26% isopropanol,23 7.5% stabilized hydrogen peroxide, 2.0% 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% or greater ortho-phthalaldehyde, and 0.08% peracetic acid with 1.0% hydrogen peroxide.24 Liquid chemical sterilants can be relied on to produce sterility only if cleaning [to eliminate organic and inorganic material] precedes treatment and if proper use as to concentration, contact time, temperature, and pH is met.25

TABLE 301-1

Methods of Sterilization and Disinfection

Modified from the works of Rutala and Simmons and their colleagues.9, 10, 13, 16, 18, 19, 303

TABLE 301-2

Summary of Advantages and Disadvantages of Chemical Agents Used as Chemical Sterilants or as High-Level Disinfectants

Modified from references 13, 93, 278, 304.

Semicritical Items

Semicritical items are those that come in contact with mucous membranes or nonintact skin. Respiratory therapy and anesthesia equipment, some endoscopes, laryngoscope blades and handles,26 esophageal manometry probes, endocavitary probes,26 nasopharyngoscopes, prostate biopsy probes,27 infrared coagulation device,28 anorectal manometry catheters, cystoscopes,29 and diaphragm fitting rings are included in this category.26 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 using chemical disinfectants. Glutaraldehyde, hydrogen peroxide, ortho-phthalaldehyde, peracetic acid, and peracetic acid with hydrogen peroxide are cleared by the U.S. Food and Drug Administration [FDA] and are dependable high-level disinfectants provided the factors influencing germicidal procedures are met [see Tables 301-1 and 301-2]. 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-log10 kill of an appropriate Mycobacterium species. Cleaning followed by high-level disinfection should eliminate sufficient pathogens to prevent transmission of infection.30, 31

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,8, 32 Legionella, 33, 34 or gram-negative bacilli such as Pseudomonas. 18, 20, 35, 36, 37 In circumstances where rinsing with sterile water rinse is not feasible, a tap water or filtered water [0.2-µm filter] rinse should be followed by an alcohol rinse and forced air drying.9, 37, 38, 39 Forced-air drying markedly reduces bacterial contamination of stored endoscopes, most likely by removing the wet environment favorable for bacterial growth.38 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 Because 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 that come 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 noncritical items in the patient environment have been quantitatively shown to be bed rails, bed surface, supply cart, overbed table, and intravenous-line 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 items36 when they are used as noncritical items and do not contact nonintact skin or mucous membranes. However, these items [e.g., bedside tables, bed rails] could potentially contribute to secondary transmission by contaminating hands of health care workers or by contact with medical equipment that will subsequently come in contact with patients.14, 42, 43, 44, 45 Table 301-1 lists several low-level disinfectants that may be used for noncritical items. The exposure time listed in Table 301-1 is equal to or greater than 1 minute. Many U.S. 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 30 to 60 seconds.42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58 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.9, 59 Because the typical drying time for a germicide on a surface is 1 to 3 minutes [unless the product contains alcohol [e.g., a 60% to 70% alcohol will dry in about 30 seconds]] [N. Omidbakhsh, written communication], one application of the germicide on all hand contact 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.60, 61 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.61 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 3 to 4 rooms, no longer than 60-minute intervals], the mopping procedure may actually spread heavy microbial contamination throughout the health care facility.62 In one study, standard laundering provided acceptable decontamination of heavily contaminated mop heads but chemical disinfection with a phenolic was less effective.62 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.63 Three other methods have been offered for monitoring patient room hygiene and they include adenosine triphosphate [ATP] bioluminescence,64, 65 fluorescent markers,66, 67 and microbiologic sampling.65 Studies have demonstrated suboptimal cleaning by aerobic colony counts as well as the use of the ATP bioluminescence and fluorescent markers.64, 66 ATP bioluminescence and fluorescent markers are preferred to aerobic plate counts because they provide an immediate assessment of cleaning effectiveness.

Disinfection of Health Care Equipment and Surfaces

A great number of disinfectants are used alone or in combinations [e.g., hydrogen peroxide and peracetic acid] in the health care setting. These include alcohols, chlorine and chlorine compounds, formaldehyde, glutaraldehyde, ortho-phthalaldehyde, standard and improved hydrogen peroxide, iodophors, peracetic acid, phenolics, and quaternary ammonium compounds. 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 the use of cleaners and disinfectants on electronic medical equipment. Problems associated with the inappropriate use of liquids on electronic medical equipment have included equipment fires, equipment malfunctions, and health care worker burns.68

Disinfectants are not interchangeable and an overview of the performance characteristics of each is provided in the next section so the user has sufficient information to select an appropriate disinfectant for any item and use it in the most efficient way. It should be recognized that excessive costs may be attributed to incorrect concentrations and inappropriate disinfectants. Finally, occupational diseases among cleaning personnel have been associated with the use of several disinfectants, such as formaldehyde, glutaraldehyde, and chlorine, and precautions [e.g., gloves, proper ventilation] should be used to minimize exposure.69 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 and Safety Health Administration [OSHA] or recommended by the National Institute for Occupational Safety and Health. The preferred method of control is to eliminate the chemical [via engineering controls, or substitution] or relocate the worker.

Chemical Disinfectants

Alcohol

In the health care setting, “alcohol” refers to two water-soluble chemical compounds, the germicidal characteristics of which are generally underrated: ethyl alcohol and isopropyl alcohol.70 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 optimal bactericidal concentration is in the range of 60% to 90% solutions in water [volume/volume].71, 72

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.73 Alcohols have been used effectively to disinfect oral and rectal thermometers, computers,60 hospital pagers, scissors, cardiopulmonary resuscitation [CPR] manikins, applanation tonometers,74 external surfaces of equipment [e.g., ventilators], and stethoscopes.75 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 liquid [e.g., sodium hypochlorite] or solid [e.g., calcium hypochlorite] forms. 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,74, 76 remove dried or fixed organisms and biofilms from surfaces,77 and have a low incidence of serious toxicity.78, 79 Sodium hypochlorite at the concentration used in domestic bleach [5.25% to 6.15%] may produce ocular irritation or oropharyngeal, esophageal, and gastric burns.69, 80, 81 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],82 and relative stability.83

Reports have examined the microbicidal activity of a new disinfectant, “superoxidized water.” The concept of electrolyzing saline to create a disinfectant or antiseptic 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].84 The free available chlorine concentrations of different superoxidized solutions reported in the literature range from 7 to 180 ppm.84 Data have shown that freshly generated superoxidized water is rapidly effective [5-log10 reduction] against a wide range of microorganisms, including glutaraldehyde-resistant mycobacteria and Bacillus atrophaeus spores.150

OPA has several potential advantages compared with glutaraldehyde. It has excellent stability over a wide pH range [pH 3 to 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.93 However, skin staining would indicate improper handling that requires additional training and/or personal protective equipment [gloves, eye and mouth protection, fluid-resistant gowns]. OPA residues remaining on inadequately water-rinsed transesophageal echocardiographic 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,153 the manufacturer has modified its instructions for use of OPA and contraindicates the use of OPA as a disinfectant for reprocessing all urologic instrumentation for patients with a history of bladder cancer. Personal protective equipment should be worn when handling contaminated instruments, equipment, and chemicals.148 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 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 it is desirable to introduce automatic endoscope reprocessors to decrease disinfectant exposure levels among scope reprocessing technicians.154

Peracetic Acid

Peracetic, or peroxyacetic acid, is characterized by a very rapid action against all microorganisms. A special advantage of peracetic acid is its lack of harmful decomposition products [i.e., acetic acid, water, oxygen, hydrogen peroxide]; it enhances removal of organic material155 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 301-2.

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 to 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 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.156, 157, 158 The sterilant, 35% peracetic acid, is diluted to 0.2% with tap water that has been filtered and exposed to ultraviolet light. Simulated-use trials with the earlier version of this processing system have demonstrated excellent microbicidal activity,74, 158, 159, 160, 161, 162 and three clinical trials have demonstrated both excellent microbial killing and no clinical failures leading to infection.163, 164, 165 Three clusters of infection using 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.166, 167 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,168, 169 it tarnishes the metal of endoscopes and is unstable, resulting in only a 24-hour use life.169

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 301-2.

The bactericidal properties of peracetic acid plus hydrogen peroxide have been demonstrated.170 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.171

The combination of peracetic acid and hydrogen peroxide has been used for disinfecting hemodialyzers.172 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 1997.173

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 on 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.15, 53, 75, 141, 174, 175, 176, 177, 178

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 high-level disinfectants for use with semicritical items but could be used to preclean or decontaminate critical and semicritical devices before terminal sterilization or high-level disinfection.

The use of phenolics in nurseries has been questioned because of the occurrence of hyperbilirubinemia in infants placed in bassinets in which phenolic detergents were used.179 In addition, Doan and co-workers demonstrated bilirubin level increases in phenolic-exposed infants compared with nonphenolic-exposed infants when the phenolic was prepared according to the manufacturers' recommended dilution.180 If phenolics [or other disinfectants] 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.18

Quaternary Ammonium Compounds

The quaternary ammonium compounds are widely used as surface disinfectants. There have been some reports of health care–associated infections associated with contaminated quaternary ammonium compounds used to disinfect patient care supplies or equipment such as cystoscopes or cardiac catheters.181, 182 As with several other disinfectants [e.g., phenolics, iodophors], gram-negative bacteria have been found to survive or grow in them.140

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.† Poor mycobactericidal activities of quaternary ammonium compounds have been reported.49, 141

The quaternaries are commonly used in ordinary environmental sanitation of noncritical surfaces such as floors, furniture, and walls. EPA-registered quaternary ammonium compounds are appropriate to use when disinfecting medical equipment that comes 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 greater than 70° C [158° F] for 30 minutes. The water temperature and time should be monitored as part of a quality assurance program.186 Pasteurization of respiratory therapy187, 188 and anesthesia equipment189 is a recognized alternative to chemical disinfection.

Ultraviolet Light

Ultraviolet [UV] light has been recognized as an effective method for killing microorganisms. It has been suggested for use in health care for several purposes, including air disinfection, room decontamination [see “Room Decontamination,” later], surface disinfection, biofilm disinfection,190 and ultrasound probe disinfection.191 Contaminated ultrasound probes can potentially transmit pathogens. When the probe is only in contact with the patient's skin there is a low risk for 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 UV light demonstrated the median microbial reduction for UV light was 100%, 87.5% for antiseptic wiping, and 88% for dry wiping.191

Surface disinfection with UV light [100-280 nm] has been evaluated with three hospital-related surfaces, namely, aluminum [bed railings], stainless steel [operating tables], and scrubs [laboratory coats]. Acinetobacter baumannii were inoculated on small coupons [103 or 105/coupon] and exposed to 90 J/m2. This exposure was effective in the inactivation of Acinetobacter from the metal coupon surfaces but ineffective in the decontamination of scrubs.192 A hand-held room decontamination technology that utilizes far-UV radiation [185 to 230 nm] to kill pathogens was evaluated and found that it rapidly kills C. difficile spores and other health care–associated pathogens on surfaces. However, the presence of organic matter reduces the efficacy of far-UV radiation, possibly explaining the more modest results observed on surfaces in hospital rooms that were not precleaned.193

Sterilization

Most medical and surgical devices used in health care facilities are made of materials that are heat stable and thus are sterilized by heat, primarily steam sterilization. However, since 1950, there has been an increase in medical devices and instruments made of materials [e.g., plastics] that require low-temperature sterilization. ETO has been used since the 1950s for heat- and moisture-sensitive medical devices. Within the past 15 years, a number of new, low-temperature sterilization systems [e.g., hydrogen peroxide gas plasma, vaporized hydrogen peroxide] have been developed and are being used to sterilize medical devices. This section reviews sterilization technologies used in health care and makes recommendations for their optimum performance in the processing of medical devices.9, 194

Sterilization destroys all microorganisms on the surface of an object or in a fluid to prevent disease transmission associated with the use of that item. Although the use of inadequately sterilized critical items represents a high risk for transmitting pathogens, documented transmission of pathogens associated with an inadequately sterilized critical item is exceedingly rare.195, 196, 197 This is likely due to the wide margin of safety associated with the sterilization processes used in health care facilities. The concept of what constitutes “sterile” is measured as a probability of sterility for each item to be sterilized. This probability is commonly referred to as the sterility assurance level [SAL] of the product and is defined as the probability of a single viable microorganism occurring on a product after sterilization. SAL is normally expressed as 10−n. For example, if the probability of a spore surviving were one in 1 million, the SAL would be 10−6.198, 199 Dual SALs [e.g., 10−3 SAL for blood culture tubes, drainage bags; 10−6 SAL for scalpels, implants] have been used in the United States for many years, and the choice of a 10−6 SAL was strictly arbitrary and not associated with any adverse outcomes [e.g., patient infections].198

Medical devices that have contact with sterile body tissues or fluids are considered critical items. These items should be sterile when used because any microbial contamination could result in disease transmission. Such items include surgical instruments, biopsy forceps, and implanted medical devices. If these items are heat resistant, the recommended sterilization process is steam sterilization, because it has the largest margin of safety due to its reliability, consistency, lethality, and least effect from organic/inorganic soils. However, reprocessing heat- and moisture-sensitive items requires use of a low-temperature sterilization technology [e.g., ETO, hydrogen peroxide gas plasma, vaporized hydrogen peroxide].200 A summary of the advantages and disadvantages for commonly used sterilization technologies is presented in Table 301-3 .

TABLE 301-3

Summary of Advantages and Disadvantages of Commonly Used Sterilization Technologies