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Disinfection and Sterilization of Patient-Care Equipment, 1985

Excerpted from the Guideline for Handwashing and Environmental Control, 1985

Section 2: Cleaning, Disinfecting, and Sterilizing Patient-Care Equipment

Introduction

Cleaning, the physical removal of organic material or soil from objects, is usually done by using water with or without detergents. Generally, cleaning is designed to remove rather than to kill microorganisms. Sterilization, on the other hand, is the destruction of all forms of microbial life; it is carried out in the hospital with steam under pressure, liquid or gaseous chemicals, or dry heat. Disinfection, defined as the intermediate measures between physical cleaning and sterilization, is carried out with pasteurization or chemical germicides.

Chemical germicides can be classified by several systems. We have used the system originally proposed by Spaulding (1) in which three levels of disinfection are defined: high, intermediate, and low (Table 1). In contrast, EPA uses a system that classifies chemical germicides as sporicides, general disinfectants, hospital disinfectants, sanitizers, and others. Formulations registered by the EPA as sporicides are considered sterilants if the contact time is long enough to destroy all forms of microbial life, or high-level disinfectants if contact times are shorter. Chemical germicides registered by the EPA as sanitizers probably fall into the category of low-level disinfectants. Numerous formulations of chemical germicides can be classified as either low- or intermediate-level disinfectants, depending on the specific label claims. For example, some chemical germicide formulations are claimed to be efficacious against Mycobacterium tuberculosis; by Spaulding's system, these formulations would be classified at least as intermediate-level disinfectants. However, chemical germicide formulations with specific label claims for effectiveness against Salmonella cholereasuis, Staphylococcus aureus, and Pseudomonas aeruginosa (the challenge microorganisms required for EPA classification as a "hospital disinfectant") could fall into intermediate- or low-level disinfectant categories.

The rationale for cleaning, disinfecting, or sterilizing patient-care equipment can be understood more readily if medical devices, equipment, and surgical materials are divided into three general categories (critical items, semicritical items, and noncritical items) based on the potential risk of infection involved in their use. This categorization of medical devices also is based on the original suggestions by Spaulding (1).

Critical items are instruments or objects that are introduced directly into the bloodstream or into other normally sterile areas of the body. Examples of critical items are surgical instruments, cardiac catheters, implants, pertinent components of the heart-lung oxygenator, and the blood compartment of a hemodialyzer. Sterility at the time of use is required for these items; consequently, one of several accepted sterilization procedures is generally recommended.

Items in the second category are classified as semicritical in terms of the degree of risk of infection. Examples are noninvasive flexible and rigid fiberoptic endoscopes, endotracheal tubes, anesthesia breathing circuits, and cystoscopes. Although these items come in contact with intact mucous membranes, they do not ordinarily penetrate body surfaces. If steam sterilization can be used, it is often cheaper to sterilize many of these items, but sterilization is not absolutely essential; at a minimum, a high-level disinfection procedure that can be expected to destroy vegetative microorganisms, most fungal spores, tubercle bacilli, and small nonlipid viruses is recommended. In most cases, meticulous physical cleaning followed by an appropriate high-level disinfection treatment gives the user a reasonable degree of assurance that the items are free of pathogens.

Noncritical items are those that either do not ordinarily touch the patient or touch only intact skin. Such items include crutches, bedboards, blood pressure cuffs, and a variety of other medical accessories. These items rarely, if ever, transmit disease. Consequently, depending on the particular piece of equipment or item, washing with a detergent may be sufficient.

The level of disinfection achieved depends on several factors, principally contact time, temperature, type and concentration of the active ingredients of the chemical germicide, and the nature of the microbial contamination. Some disinfection procedures are capable of producing sterility if the contact times used are sufficiently long; when these procedures are continued long enough to kill all but resistant bacterial spores, the result is high-level disinfection. Other disinfection procedures that can kill many types of viruses and most vegetative microorganisms (but cannot be relied upon to kill resistant microorganisms such as tubercle bacilli, bacterial spores, or certain viruses) are considered to be intermediate- or low-level disinfection (Table1).

The tubercle bacillus, lipid and nonlipid viruses, and other groups of microorganisms in Table I are used in the context of indicator microorganisms that have varying degrees of resistance to chemical germicides and not necessarily because of their importance in causing nosocomial infections. For example, cells of M. tuberculosis or M. bovis, which are used in routine efficacy tests, are among the most resistant vegetative microorganisms known and, after bacterial endospores, constitute the most severe challenge to a chemical germicide. Thus, a tuberculocidal chemical germicide may be used as a high or intermediate-level disinfectant targeted to many types of nosocomial pathogens but not specifically to control respiratory tuberculosis.

Control Measures

Since it is neither necessary nor possible to sterilize all patient-care items, hospital policies can identify whether cleaning, disinfecting, or sterilizing of an item is indicated to decrease the risk of infection. The process indicated for an item will depend on its intended use. Any microorganism, including bacterial spores, that come in contact with normally sterile tissue can cause infection. Thus, it is important that all items that will touch normally sterile tissues be sterilized. It is less important that objects touching mucous membranes be sterile. Intact mucous membranes are generally resistant to infection by common bacterial spores but are not resistant to many other microorganisms, such as viruses and tubercle bacilli; therefore, items that touch mucous membranes require a disinfection process that kills all but resistant bacterial spores. In general, intact skin acts as an effective barrier to most microorganisms; thus, items that touch only intact skin need only be clean.

Items must be thoroughly cleaned before processing, because organic material (e.g., blood and proteins) may contain high concentrations of microorganisms. Also, such organic material may inactivate chemical germicides and protect microorganisms from the disinfection or sterilization process. For many noncritical items, such as blood pressure cuffs or crutches, cleaning can consist only of 1) washing with a detergent or a disinfectant-detergent, 2) rinsing, and 3) thorough drying.

Steam sterilization is the most inexpensive and effective method for sterilization. Steam sterilization is unsuitable, however, for processing plastics with low melting points, powders, or anhydrous oils. Items that are to be sterilized but not used immediately need to be wrapped for storage. Sterility can be maintained in storage for various lengths of time, depending on the type of wrapping material, the conditions of storage, and the integrity of the package.

Several methods have been developed to monitor steam sterilization processes. One method is to check the highest temperature that is reached during sterilization and the length of time that this temperature is maintained. In addition, heat- and steam-sensitive chemical indicators can be used on the outside of each pack. These indicators do not reliably document sterility, but they do show that an item has not accidentally bypassed a sterilization process. As an additional precaution, a large pack might have a chemical indicator both on the outside and the inside to verify that steam has penetrated the pack.

Microbiological monitoring of steam sterilizers is recommended at least once a week with commercial preparations of spores of Bacillus stearothermophilus (a microorganism having spores that are particularly resistant to moist heat, thus assuring a wide margin of safety). If a sterilizer is working properly and used appropriately, the spores are usually killed. One positive spore test (spores not killed) does not necessarily indicate that items processed in the sterilizer are not sterile, but it does suggest that the sterilizer should be rechecked for proper temperature, length of cycle, loading, and use and that the test be repeated. Spore testing of steam sterilization is just one of several methods for assuring adequate processing of patient-care items (Table 2).

Implantable items, such as orthopedic devices, require special handling before and during sterilization; thus, packs containing implantable objects need to be clearly labeled so they will be appropriately processed. To guarantee a wide margin of safety, it is recommended that each load of such items be tested with a spore test and that the sterilized item not be released for use until the spore test is negative at 48 hours. If it is not possible to process an implantable object with a confirmed 48-hour spore test before use, it is recommended that the unwrapped object receive the equivalent of full-cycle steam sterilization and not flash sterilization. Flash sterilization [270°F (132°C) for 3 minutes in a gravity displacement steam sterilizer] is not recommended for implantable items because spore tests cannot be used reliably and the margin of safety is lower.

Because ethylene oxide gas sterilization is a more complex and expensive process than steam sterilization, it is usually restricted to objects that might be damaged by heat or excessive moisture. Before sterilization, objects also need to be cleaned thoroughly and wrapped in a material that allows the gas to penetrate. Chemical indicators need to be used with each package to show that it has been exposed to the gas sterilization process. Moreover, it is recommended that gas sterilizers be checked at least once a week with commercial preparations of spores, usually Bacillus subtilis var. niger. Because ethylene oxide gas is toxic, precautions (e.g., local exhaust ventilation ) should be taken to protect personnel (2). All objects processed by gas sterilization also need special aeration according to manufacturer's recommendations before use to remove toxic residues of ethylene oxide.

Powders and anhydrous oils can be sterilized by dry heat. Microbiological monitoring of dry heat sterilizers and following manufacturers' recommendations for their use and maintenance usually provides a wide margin of safety for dry heat sterilization.

Liquid chemicals can be used for sterilization and disinfection when steam, gas, or dry heat sterilization is not indicated or available. With some formulations, high-level disinfection can be accomplished in 10-30 minutes, and sterilization can be achieved if exposure is for significantly longer times. Nevertheless, not all formulations are equally applicable to all items that need to be sterilized or disinfected. No formulation can be considered as an "all purpose" chemical germicide. In each case, more detailed information can be obtained from the EPA, descriptive brochures from the manufacturers, peer-review journal articles, and books. The most appropriate chemical germicide for a particular situation can be selected by responsible personnel in each hospital based on the object to be disinfected, the level of disinfection needed, and the scope of services, physical facilities, and personnel available in the hospital. It is also important that the manufacturer's instructions for use be consulted.

Gloves may be indicated to prevent skin reactions when some chemical disinfectants are used. Items subjected to high-level disinfection with liquid chemicals need to be rinsed in sterile water to remove toxic or irritating residues and then thoroughly dried. Subsequently, the objects need to be handled aseptically with sterile gloves and towels and stored in protective wrappers to prevent recontamination.

Hot-water disinfection (pasteurization) is a high-level, nontoxic disinfection process that can be used for certain items, e.g., respiratory therapy breathing circuits.

In recent years, some hospitals have considered reusing medical devices labeled disposable or single use only. In general, the primary, if not the sole, motivation for such reuse is to save money. For example, the disposable hollow-fiber hemodialyzer has been reprocessed and reused on the same patient in hemodialysis centers since the early 1970s. By 1984, 51% of the 1,200 U.S. dialysis centers were using dialyzer reprocessing programs. It has been estimated that this practice saves more than 100 million dollars per year (3). When standard protocols for cleaning and disinfecting hemodialyzers are used, there does not appear to be any significant infection risk to dialysis patients (4). Moreover, the safety and efficacy of dialyzer reuse programs are supported by several major studies (5-7). Few, if any, other medical devices that might be considered candidates for reprocessing have been evaluated in this manner.

Arguments for and against reprocessing and reusing single-use items in the 1980's have been summarized (4). Since there is lack of evidence indicating increased risk of nosocomial infections associated with reusing all single-use items, a categorical recommendation against all types of reuse is not considered justifiable. Rather than recommending for or against reprocessing and reuse of all single-use items, it appears more prudent to recommend that hospitals consider the safety and efficacy of the reprocessing procedure of each item or device separately and the likelihood that the device will function as intended after reprocessing. In many instances it may be difficult if not impossible to document that the device can be reprocessed without residual toxicity and still function safely and effectively. Few, if any, manufacturers of disposable or single-use medical devices provide reprocessing information on the product label.

Hydrotherapy pools and immersion tanks present unique disinfection problems in hospitals. It is generally not economically feasible to drain large hydrotherapy pools that contain thousands of gallons of water after each patient use. Typically, these pools are used by a large number of patients and are drained and cleaned every one to two weeks. The water temperature is typically maintained near 37°C. Between cleanings, water can be contaminated by organic material from patients, and high levels of microbial contamination are possible. One method to maintain safe pool water is to install a water filter of sufficient size to filter all the water at least three times per day and to chlorinate the water so that a free chlorine residual of approximately 0.5 mg/l is maintained at a pH of 7.2 to 7.6. Local public health authorities can provide consultation regarding chlorination, alternate halogen disinfectants, and hydrotherapy pool sanitation.

Hubbard and immersion tanks present entirely different problems than large pools, since they are drained after each patient use. All inside surfaces need to be cleaned with a disinfectant-detergent, then rinsed with tap water. After the last patient each day, an additional disinfection step is performed. One general procedure is to circulate a chlorine solution (200-300 mg/l) through the agitator of the tank for 15 minutes and then rinse it out. It is also recommended that the tank be thoroughly cleaned with a disinfectant-detergent, rinsed, wiped dry with clean cloths, and not filled until ready for use.

An alternative approach to control of contamination in hydrotherapy tanks is to use plastic liners and create the "whirlpool effect" without agitators. Such liners make it possible to minimize contact of contaminated water with the interior surface of the tank and also obviate the need for agitators that may be very difficult to clean and decontaminate.

Recommendations

1. Cleaning

   All objects to be disinfected or sterilized should first be thoroughly cleaned to remove all organic matter (blood and tissue) and other residue. Category I

2. Indications for Sterilization and High-Level Disinfection
   1. Critical medical devices or patient-care equipment that enter normally sterile tissue or the vascular system or through which blood flows should be subjected to a sterilization procedure before each use. Category I
   2. Laparoscopes, arthroscopes, and other scopes that enter normally sterile tissue should be subjected to a sterilization procedure before each use; if this is not feasible, they should receive at least high-level disinfection. Category I
   3. Equipment that touches mucous membranes, e.g., endoscopes, endotracheal tubes, anesthesia breathing circuits, and respiratory therapy equipment, should receive high-level disinfection. Category I
3. Methods of Sterilization
   1. Whenever sterilization is indicated, a steam sterilizer should be used unless the object to be sterilized will be damaged by heat, pressure, or moisture or is otherwise inappropriate for steam sterilization. In this case, another acceptable method of sterilization should be used. Category II
   2. Flash sterilization [270°F (132°C) for 3 minutes in a gravity displacement steam sterilizer] is not recommended for implantable items. Category II
4. Biological Monitoring of Sterilizers
   1. All sterilizers should be monitored at least once a week with commercial preparations of spores intended specifically for that type of sterilizer (i.e., Bacillus stearothermophilus for steam sterilizers and Bacillus subtilis for ethylene oxide and dry heat sterilizers). Category II
   2. Every load that contains implantable objects should be monitored. These implantable objects should not be used until the spore test is found to be negative at 48 hours. Category II
   3. If spores are not killed in routine spore tests, the sterilizer should immediately be checked for proper use and function and the spore test repeated. Objects, other than implantable objects, do not need to be recalled because of a single positive spore test unless the sterilizer or the sterilization procedure is defective. Category II
   4. If spore tests remain positive, use of the sterilizer should be discontinued until it is serviced. Category I
5. Use and Preventive Maintenance

   Manufacturers' instructions should be followed for use and maintenance of sterilizers.
   Category II

6. Chemical Indicators

   Chemical indicators that will show a package has been through a sterilization cycle should be visible on the outside of each package sterilized. Category II

7. Use of Sterile Items

   An item should not be used if its sterility is questionable, e.g., its package is punctured, torn, or wet. Category I

8. Reprocessing Single-Use or Disposable Items
   1. Items or devices that cannot be cleaned and sterilized or disinfected without altering their physical integrity and function should not be reprocessed. Category I
   2. Reprocessing procedures that result in residual toxicity or compromise the overall safety or effectiveness of the items or devices should be avoided. Category I

References

1. Favero MS. Chemical disinfection of medical and surgical materials. In: Block SS, ed. Disinfection, sterilization and preservation. 3rd ed. Philadelphia: Lea and Febiger, 1983;469-92.
2. Fed Reg June 22, 1984, 29 CFR 1910, Occupational Exposure to Ethylene Oxide.
3. Romeo AA. The economics of reuse. In: Reuse of disposable medical devices in the 1980's. Proceedings of International Conference on the Reuse of Disposable Medical Devices in the 1980's, The Institute for Health Policy Analysis. Georgetown University Medical Center, 1984 Mar 29-30. Washington, D.C.: Institute for Health Policy Analysis. 1984:43-9.
4. Institute for Health Policy Analysis, Georgetown University Medical Center. Proceedings of International Conference on the Reuse of Disposable Medical Devices in the 1980's. March 29-30, 1984. Washington, D.C.
5. Jacobs C, Brunner FP, Chantler C, et al. Combined report on regular dialysis and transplantation in Europe VII. 1976. Proc Eur Dial Transplant Assoc 1977;14:3-69.
6. Levin N. Dialyzer re-use in a hospital. Dial and Transplant 1980;9(1):40-6.
7. Wing AJ, Brunner FP, Brunner FP, et al. Mortality and morbidity of reusing dialyzers. Br Med J 1978;2:853-5.

Table 1. Levels of Disinfection According to Type of Microorganism

Levels	Vegetative	Bacteria     Tubercle Bacillus	Spores	Fungi1	Viruses
					Lipid & Medium Size	Nonlipid & Small
High	+2	+	+3	+	+	+
Intermediate	+	+	±4	+	+	±5
Low	+	-	-	±	+	-

¹Includes asexual spores but not necessarily chlamydospores or sexual spores.
²Plus sign indicates that a killing effect can be expected when the normal use-concentrations of chemical disinfectants or pasteurization are properly employed; a negative sign indicates little or no killing effect.
³0nly with extended exposure times are high-level disinfectant chemicals capable of actual sterilization.
⁴Some intermediate-level disinfectants can be expected to exhibit some sporicidal action.
⁵Some intermediate-level disinfectants may have limited virucidal activity.

Table 2. Methods of Assuring Adequate Processing and Safe Use of Medical Devices

Object and Classification	Example	Method	Comment
PATIENT-CARE OBJECTS
Critical
Sterilized in the hospital	Surgical instruments and devices; trays and sets	1. Thoroughly clean objects and wrap or package for sterilization. 2. Follow manufacturer's instructions for use of each sterilizer or use recommended protocol. 3. Monitor time-temperature charts. 4. Use commercial spore preparations to monitor sterilizers. 5. Inspect package for integrity and for exposure of sterility indicator before use. 6. Use before maximum safe storage time has expired if applicable.	Sterilization processes are designed to have a wide margin of safety. If spores are not killed, the sterilizer should be checked for proper use and function, if spore tests remain positive, discontinue use of the sterilizer until properly serviced. Maximum safe storage time of items processed in the hospital varies according to type of package or wrapping material(s) used; follow manufacturer's instructions for use and storage times.
Purchased as Sterile	Intravenous fluids; irrigation fluids; normal saline; trays and sets	1. Store in safe, clean area. 2. Inspect package for integrity before use. 3. Use before expiration date if one is given. 4. Culture only if clinical circumstances suggest infection related to use of the item.	Notify the Food and Drug Administration, local and state health departments, and CDC if intrinsic contamination is suspected.
Semicritical
Should be free of vegetative bacteria. May be subjected to high-level disinfection rather than sterilization process	Respiratory therapy equipment and instruments that will touch mucous membranes	1. Sterilize or follow a protocol for high-level disinfection. 2. Bag and store in safe, clean area. 3. Conduct quality control monitoring after any important changes in the disinfection process.	Bacterial spores may survive after high-level disinfection, but these usually are not pathogenic. Microbiologic sampling can verify that a high-level disinfection process has resulted in destruction of vegetative bacteria, however, this sampling is not routinely recommended.
Non critical
Usually contaminated with some bacteria	Bedpans; crutches; rails; EKG leads	1. Follow a protocol for cleaning or, if necessary a low-level disinfection process.
Water produced or treated	Water used for hemodialysis fluids	1. Assay water and dialysis fluids monthly. 2. Water should not have more than 200 bacteria/ml and dialysis fluids not more than 2000 bacteria/ml.	Gram-negative water bacteria can grow rapidly in water and dialysis fluids and can place dialysis patients at risk of pyrogenic reactions or septicemia. These water sources and pathways should be disinfected routinely.

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