Decontamination, Disinfection, and Sterilization

PRINCIPLES OF TERMINOLOGY, DEFINITIONS, AND

CLASSIFICATION OF MEDICAL DEVICES Back to top

Background

There is no uniform terminology for disinfection and sterilization, and many problems arise

as a result. Many terms are ill defined even within the United States or Europe. In addition,

the testing procedures for disinfectants are not as far advanced and well defined as MIC

testing based on the recommendations of the Clinical and Laboratory Standards Institute

(CLSI). However, there currently are efforts to standardize and harmonize the terminology

on an international level. For example, the International Organization for Standardization

(ISO) norms for sterilization were published in 2004 and included in the new guidelines

published in 2010 (229). In addition, manufacturers now must provide specific data on how

to reprocess their medical devices. In the past, such information was frequently missing in

the user’s manuals.

Classification of Devices for Reprocessing

Background

The principal goal of disinfection and sterilization is to reduce the numbers of microorganisms

on a device to a level that is insufficient to transmit infectious organisms, with a considerable

safety margin. The most conservative approach would be to reprocess all items and devices

with overkill sterilization. Obviously, not all items must undergo the most vigorous process to

eliminate any microorganisms. For example, items such as blood pressure cuffs that are used

at nonsterile body sites do not need to be sterilized between patients. In contrast, only

sterilization will eliminate any risk of infection for devices used in a normally sterile body

site. In some cases, the best choice may be to use disposable items instead of reusable

devices, because reprocessing may be more expensive or does not provide the desired level

of safety. The latter may apply to items in contact with neural tissue of a patient suffering

from any form of CJD or with tonsils and other lymphatic tissues of persons with spongiform

encephalopathy (bovine spongiform encephalopathy [BSE] or vCJD) (25, 70, 280).

Therefore, devices must be classified to allow staff to define the appropriate method for

disinfection and/or sterilization for each item. A classification system should balance the

potential risks for transmission of infection (e.g., the infectious dose) and the resources

available to achieve the necessary or desired level of antimicrobial killing. The most

commonly used classification was proposed by Earle H. Spaulding in 1968 (249). He

proposed three categories that are based on the devices’ potential for transmitting infectious

agents: critical, semicritical, and noncritical (Table 1). The Centers for Disease Control and

Prevention (CDC) cites this classification in its Guidelines for Handwashing and Hospital

Environmental Control(http://www.cdc.gov/mmwr/PDF/rr/rr5116.pdf), as does the U.S. Food

and Drug Administration (FDA), for approval of sterilants and high-level disinfectants

(see http://www.fda.gov/MedicalDevices/ DeviceRegulationandGuidance/

ReprocessingofSingle-UseDevices/ucm133514.htm). Most infection control professionals

worldwide use this classification as well. However, this simple classification does not work

perfectly for all devices. Even the definition of sterilization as the absence of any viable

microorganisms must be revised to address the prions responsible for CJD and vCJD (202).

Overview of Commonly Used Disinfectants for Devices

Glutaraldehyde

Among aldehydes that exhibit biocidal activity, including glyoxal, ortho-phthalaldehyde

(OPA), succinaldehyde, and benzaldehydes, glutaraldehyde and formaldehyde are the most

extensively studied aldehydes. In-depth reviews may be found elsewhere (19, 213, 216).

In commercially available products, glutaraldehyde is the predominant aldehyde. Because it

has potent and broad-spectrum microbicidal activity and is compatible with many materials

(including metal, rubber, and plastic), glutaraldehyde is often regarded as the high-level

disinfectant and chemical sterilant of choice in many health care facilities. Glutaraldehydebased

formulations are most commonly used for high-level disinfection of medical equipment

such as endoscopes, transducers, dialysis systems, and anesthesia and respiratory therapy

equipment (216). The mechanism of action is complex and is related to alkylation of

sulfhydryl, hydroxyl, carboxy, and amino groups in the cell wall, cell membrane, nucleic

acids, enzymes, and other proteins of microorganisms. The biocidal activities of

glutaraldehyde solutions are dependent on a variety of variables, such as pH, temperature,

concentration at the time of use, the presence of inorganic ions, and the age of the solution

(19). Aqueous solutions of glutaraldehyde are usually acidic and are not sporicidal in this

form. Therefore, they need to be activated by adding an alkalinizing agent. These activated

solutions, however, rapidly lose their activity because glutaraldehyde molecules polymerize

at an alkaline pH. Therefore, the shelf life of such solutions is limited to 14 days unless the

manufacturer recommends otherwise. To overcome this problem, some manufacturers have

developed novel formulations with longer shelf lives (e.g., activated dialdehyde solutions

containing 2.4 to 3.5% glutaraldehyde with a maximum reuse life of 28 days).

The activities of disinfectants increase as the temperature rises. Among eight disinfectants

tested, glutaraldehyde was found to be the chemical most strongly affected by temperature

(108). Some stable acid glutaraldehydes may be used at temperatures of 35 to 55°C at

concentrations below 2%. Glutaraldehyde retains its activity in the presence of organic

matter. A standard 2% aqueous solution of glutaraldehyde buffered to pH 7.5 to 8.5 is

bactericidal, tuberculocidal, sporicidal, fungicidal, and virucidal. It rapidly kills both gramnegative

and gram-positive vegetative bacteria. Longer exposure times are required to

inactivate spores and mycobacteria. Spores of Bacillus and Clostridium spp. are generally

destroyed by 2% glutaraldehyde in 3 h, whereas spores of Clostridium difficile are eliminated

more rapidly (221). In contrast,Cryptosporidium parvum oocysts remained viable and

infectious after 10 h in a 2.5% glutaraldehyde solution (290). Several investigators have

questioned glutaraldehyde’s ability to inactivate mycobacteria. For example, Rubbo et al.

(212) demonstrated that glutaraldehyde more slowly inactivated Mycobacterium

tuberculosis than did alcohols, formaldehyde, iodine, and phenol. Ascenzi (19) showed in the

quantitative suspension test that 2% glutaraldehyde killed only 2 to 3 log units of M.

tuberculosis in 20 min at 20°C. Similarly, Collins (69) reported that glutaraldehyde could not

completely inactivate a standardized suspension of M. tuberculosiswithin 10 min.

Nontuberculous mycobacteria such as Myobacterium avium, Myobacterium intracellulare,

andMyobacterium gordonae are more resistant to inactivation than M. tuberculosis (68).

These and other data suggest that 20 min (at 20°C) is the minimum exposure time needed

to reliably inactivate tuberculous and nontuberculous mycobacteria by 2% glutaraldehyde,

provided that the contaminated item has been thoroughly cleaned before disinfection

(140, 216). Glutaraldehyde-resistant mycobacteria have been isolated from endoscope

washer-disinfectors (116, 269; see “ Endoscopes” below). The virucidal activity of

glutaraldehyde extends to the nonenveloped (hydrophilic) viruses, which are generally more

resistant to disinfectants than are the enveloped (lipophilic) viruses. Numerous viruses were

documented to be inactivated, including HIV, hepatitis A virus (HAV), HBV, poliovirus type 1,

coxsackievirus type B, yellow fever virus, and rotavirus (19, 151). The disadvantages of

glutaraldehyde include the fact that it coagulates blood and can fix proteins and tissue to

surfaces (177, 216). In addition, glutaraldehyde has a pungent and irritating odor and its

vapor at the level of 0.2 ppm irritates the eyes, throat, and nose. HCWs exposed to

glutaraldehyde can develop allergic contact dermatitis, asthma, rhinitis, and epistaxis.

Measures that may minimize employee exposure include covering immersion baths with

tight-fitting lids, improved ventilation, ducted exhaust hoods or ductless fume hoods with

vapor absorbents, personal protective equipment, and appropriate automated machines for

endoscope disinfection (12, 216). Due to dilution, glutaraldehyde concentrations commonly

decline during use in manual and automatic baths used for endoscopes (177). Test strips

should be used to ensure that the glutaraldehyde concentration has not fallen below 1 to

1.5%. Equipment disinfected with glutaraldehyde and rinsed inadequately has caused serious

clinical complications including proctocolitis (colonoscopes), (87, 282); and keratopathy

(ophthalmic instruments). Because the infectivity of prions can be stabilized when

instruments are treated with formaldehyde before they are autoclaved (48), aldehydes are

no longer recommended for disinfecting endoscopes in some European countries (e.g.,

France) (see “Bovine Spongiform Encephalopathy and Variant Creutzfeldt- Jakob Disease”

below).

ortho-Phthalaldehyde

A 0.55% OPA solution has been approved as a high-level disinfectant by the FDA and by

agencies in other countries. However, different countries or areas have set different

exposure times for a 0.55% solution of OPA at 20°C to achieve high-level disinfection: 12

min in the United States, 10 min in Canada, and 5 min in Europe, Asia, and Latin America.

Compared with glutaraldehyde, OPA has several advantages: (i) it does not require

activation; (ii) it is compatible with many materials (i.e., similar to glutaraldehyde); (iii) it is

more stable during storage and reuse as well as at a wide pH range of 3 to 9; (iv) it has low

vapor properties; (v) its odor is barely perceptible; (vi) it is more rapidly mycobactericidal

than glutaraldehyde in vitro and has good activity against glutaraldehyde-resistant strains at

longer exposure times (102). However, 0.5% OPA is slowly sporicidal and does not inactivate

all spores within 270 min of exposure (273). In addition, OPA stains proteins, skin, clothing,

and instruments. OPA vapors may irritate the respiratory tract and eyes. At present, the

effects of long-term exposure and safe exposure levels are not well defined. Therefore, OPA

must be handled with appropriate safety precautions (i.e., gloves, fluid-resistant gowns, and

eye protection) and it must be stored in containers with tight-fitting lids. If additional studies

corroborate OPa ’s advantages, this compound may replace glutaraldehyde for many uses,

especially endoscope disinfection. The new agent appears to be particularly useful in washerdisinfectors,

where glutaraldehyde-resistant mycobacteria have emerged (269, 273).

Formaldehyde

Formaldehyde and its condensates are reviewed in depth elsewhere (207). Formaldehyde in

aqueous solutions or as a gas has been used as a disinfectant and sterilant for many

decades. Its use in the health care setting, however, has sharply decreased for several

reasons. The irritating vapors and pungent odor produced by formaldehyde are apparent at

very low levels (<1 ppm). Moreover, allergy to formaldehyde is fairly common. In addition,

the Occupational Safety and Health Administration in the United States and the Health and

Safety Executive of the United Kingdom indicated that formaldehyde vapors may be

carcinogenic. Thus, the Occupational Safety and Health Administration limits the 8-h timeweighted

average exposure in the workplace to a concentration of 0.75 ppm. Elevated levels

of occupational exposures have been found among workers in dialysis units and gross

anatomy laboratories (8). Consequently, formaldehyde and formaldehyde-releasing agents

are used infrequently in health care institutions, despite this agent’s broad-spectrum

microbicidal activity. In fact, formaldehyde has been largely replaced by peracetic acid as an

agent for disinfecting hemodialysis equipment and water dialysate tubing systems.

Paraformaldehyde vaporized by heat is used to decontaminate biological safety cabinets.

Chlorine and Chlorine-Releasing Compounds

Due to its hazardous nature, chlorine gas is rarely used as a disinfectant. Among the large

number of chlorine compounds commercially available, hypochlorites are the most widely

used disinfectants. Hypochlorite has been used for more than a century and remains an

important disinfectant. Rutala and Weber published an extensive review of uses for inorganic

hypochlorite in health care facilities (225), and Karol reviewed the potential hazards and

significant benefits of chlorine use (148). Aqueous solutions of sodium hypochlorite are

usually called household bleach. Bleach commonly contains 5.25% sodium hypochlorite or

52,500 ppm available chlorine; a 1:10 dilution of bleach provides about 300 to 600 mg of

free chlorine per liter. Alternative chlorine-releasing compounds frequently used in health

care facilities include chloramine-T, sodium dichloroisocyanurate tablets, and chlorine

dioxide. Demand-release chlorine dioxide is an extremely reactive compound and must be

prepared at the point of use. It is used primarily to chlorinate potable water, swimming

pools, and wastewater. In Europe, commercial chlorine dioxide preparations are available to

disinfect instruments. In aqueous solution, all chlorine compounds release hypochlorous acid,

the most likely active compound. The mechanism of microbicidal action of hypochlorous acid

has not been fully elucidated, but it inhibits key enzymatic reactions within cells and

denaturates proteins. Lowering the pH or raising the temperature or concentration increases

its antimicrobial efficacy. Chlorine compounds have broad antimicrobial spectra including, at

higher concentrations, bacterial spores and M. tuberculosis. Therefore, hypochlorite can be

used as a high-level disinfectant for semicritical items. Concentrations of 100 ppm of

available chlorine inactivate vegetative bacteria and viruses in 10 min. Suspension tests

document that both enveloped and nonenveloped viruses, including HIV, HAV, HBV, herpes

simplex virus types 1 and 2, poliovirus, coxsackievirus, and rotavirus are inactivated (225).

In one study, a concentration of 100 ppm chlorine eliminated 99.9% ofBacillus

subtilis endospores in 5 min (289). However, endospore-forming bacteria, mycobacteria,

fungi, and protozoa usually are less susceptible to chlorine than other microorganisms, and

high concentrations of chlorine (1,000 ppm) are required to completely destroy them.

Despite this limitation, sodium hypochlorite solutions (500 ppm and 1,600 ppm) have been

reported to decrease C. difficile environmental contamination and terminate outbreaks of

infections caused by this organism (143). Cryptosporidium oocysts are particularly resistant

to chlorine. These oocysts remain infective for several days in swimming pool water

containing recommended chlorine concentrations, and because of their small size they may

not be removed efficiently by conventional pool filters. Outbreaks of cryptosporidium

infections have been associated with drinking water and swimming pools (54). Of note,

chloramine-T and sodium dichloroisocyanurate seem to have less sporicidal action than does

sodium hypochlorite. Hypochlorite is fast acting, nonstaining, nonflammable, and

inexpensive. However, its use is limited because it is corrosive, inactivated by organic

matter, and relatively instable. Sodium hypochlorite can injure tissue; however, this occurs

rarely in health care facilities (225). Inhalation of chlorine gas may irritate the respiratory

tract, resulting in cough, dyspnea, and pulmonary edema or chemical pneumonitis. The

potential carcinogens trihalomethanes have been detected in chlorine-treated water, and

high levels of trihalomethanes can be detected when hospitals hyperchlorinate their water

systems (127).

Chlorine compounds have other important disadvantages. Blood or other organic matter

substantially inactivates hypochlorites and other chlorine compounds. Consequently, items

used for patient care and environmental surfaces must be cleaned before hypochlorite is

used. In addition, biofilm (e.g., in the pipes of a water distribution system) also reduces the

efficacy of chlorines significantly. Moreover, the free available chlorine levels in solutions can

decay to 40 to 50% of the original concentration after the container has been opened for 1

month. Therefore, concentrations higher than those established in laboratory experiments

should be used in practice. Loss of free chlorine can be minimized if the solutions are kept

and used at room temperature, in dilution, in an alkaline pH range, and stored in closed

opaque containers.

Depending on the concentrations employed, sodium hypochlorite is used in hospitals as a

high-level disinfectant for selected semicritical devices (e.g., dental equipment and

mannequins used for cardiopulmonary resuscitation training), as an intermediate-level

disinfectant (e.g., hemodialysis equipment), and as a low-level disinfectant for environmental

surfaces and hydrotherapy tanks. For example, the CDC recommends that HCWs use a

1:100 dilution (5,000 ppm) of hypochlorite to decontaminate spills of blood and certain other

body fluids (55). Because chlorine can be inactivated by blood and other organic material, a

full-strength solution or a 1:10 dilution will be safer unless the surface is cleaned before it is

disinfected (64, 97,276). Household bleach also can be used to disinfect tabletops,

incubators, and spills in laboratories or to disinfect syringes used by drug addicts if sterile

disposable syringes are not available (56). At low concentrations, chlorines (usually about

0.5 ppm free chlorine) are used to chlorinate the drinking water. Hyperchlorination of

institutional water systems has controlled epidemics caused by Legionella pneumophila(127)

but also corrodes the water distribution system (127). Stabilized solutions of chlorine dioxide

appear to be less toxic and more efficacious than chlorine for controlling growth of

legionellae (122). A growing number of municipal water treatment plants in the United

States are using monochloramine as a residual disinfectant. Chloramination of drinking water

has several advantages compared to the use of free chlorine, including decreasing the risk of

Legionnaires’ disease at the municipal level or in individual hospitals (154). However,

outbreaks of Cryptosporidium infections have occurred in cities that use chloramines in their

drinking water.

Hydrogen Peroxide

Hydrogen peroxide, a strong oxidizer, is used for high-level disinfection and sterilization. It

produces destructive hydroxyl free radicals that attack membrane lipids, DNA, and other

essential cell components. Although the catalase produced by anaerobic and some aerobic

bacteria may protect cells from hydrogen peroxide, this defense is overwhelmed by the

concentrations used for disinfection (164). Generally, a 3% hydrogen peroxide solution is

rapidly bactericidal, but it kills organisms with high cellular catalase activity (e.g.,S.

aureus and Serratia marcescens) less rapidly. Surprisingly, 3% hydrogen peroxide was

ineffective against vancomycin-resistant enterococci (174, 239). Spores are more resistant

than vegetative bacteria to hydrogen peroxide. For example, a 3% solution of hydrogen

peroxide destroyed 106 spores in six of seven exposure trials that were 150 min long; a 10%

solution was always successful in 60 min (275). Higher concentrations of hydrogen peroxide

(17.7 and 35.4%) killed Bacillus subtilis spores in 9.4 and 2.3 min, respectively (162). In a

recent investigation, 10% hydrogen peroxide was the most active of the seven chemical

disinfectants tested against B. subtilis spores (234). However, other investigators found that

the sporicidal activity of hydrogen peroxide was lower than those of peracetic acid and

chlorine (10). Hydrogen peroxide’s sporicidal activity can be enhanced by increasing the

concentration or temperature or by using it in conjunction with ultrasonic energy, UV

radiation, and some chemical agents such as peracetic acid (172, 180, 265). A 0.3% solution

of hydrogen peroxide is able to inactivate HIV in 10 min (172), and a 3% concentration

inactivates rhinovirus in 6 to 8 min at 37°C (180). However, a 6% solution was ineffective

against poliovirus at 1 min (265). Hydrogen peroxide does not coagulate blood and does not

fix tissues to surfaces. In fact, it may enhance removal of organic material from equipment.

Hydrogen peroxide has a low toxicity for humans. It decomposes to oxygen and water, and

therefore, it is environmentally safe. It is neither carcinogenic nor mutagenic. Concentrated

solutions may irritate the eyes, skin, and mucous membranes. Hydrogen peroxide can be

destroyed easily by heat or enzymes (catalase and peroxidases). Stabilized solutions can be

used for high-level disinfection of semicritical items, considering the corrosive effects of

hydrogen peroxide on copper, zinc, and brass (216). The FDA has approved commercial

products containing either 7.5% hydrogen peroxide alone or combinations with peracetic acid

as liquid sterilants and high-level disinfectants for processing reusable medical and dental

devices (www.fda.gov) (232). Concentrations of 3 to 6% are used to disinfect ventilators,

soft contact lenses (3% for 2 to 4 h) (134), and tonometer biprisms (163, 164, 216).

Vaporized hydrogen peroxide is also used for plasma sterilization (see below). Despite its

limited toxicity, hydrogen peroxide can damage human tissues. Patients exposed to

endoscopes contaminated by residual hydrogen peroxide have developed pseudomembranelike

enterocolitis (pseudolipomatosis) (232). In addition, patients who were exposed to

tonometer tips disinfected with hydrogen peroxide and rinsed improperly suffered corneal

damage (163). Use of hydrogen peroxide to clean wounds and in dental regimens remains

controversial (164).

Peracetic Acid

Peracetic acid (or peroxyacetic acid) is a more potent germicidal agent than hydrogen

peroxide and was the most active agent in several in vitro studies (9, 235). Concentrations

of ≤1% are sporicidal even at low temperatures. The mechanism of action of peracetic acid

has not been fully elucidated, but its mechanism of action is likely to be similar to that of

hydrogen peroxide and other oxidizing agents. Peracetic acid remains effective in the

presence of organic matter. At low concentrations it is considerably less stable than

hydrogen peroxide; preparations with appropriate stability have been developed and are

commercially available. Peracetic acid corrodes steel, galvanized iron, copper, brass, and

bronze, and it attacks natural and synthetic rubbers. In addition, concentrated solutions can

seriously damage eyes and skin. Furthermore, some investigators have raised concerns

about the potential toxicity of the combination of peracetic and acetic acids (126). Feldman

et al. reported that mortality rates in freestanding dialysis facilities that reprocessed

dialyzers with peracetic and acetic acid were higher than in facilities that discarded dialysis

filters or used formaldehyde for reprocessing (94). To date, investigators have not

determined whether the higher death rate was caused by the disinfectants or was associated

with other practices at the facilities or with patient risk factors. Nevertheless, because

peracetic acid has powerful germicidal activity and does not produce toxic residues, peracetic

acid is very attractive for use in health care settings, most frequently in combination with

hydrogen peroxide to disinfect hemodialyzers. The FDA lists several commercial products

containing a combination of peracetic acid and hydrogen peroxide as high-level disinfectants

and chemical sterilants. The use of peracetic acid for chemical sterilization of instruments

and endoscopes (Steris System 1) is discussed below.

Alcohols

For centuries, the alcohols have been appreciated for their antimicrobial properties. Alcohol is

defined by the FDA as having one of the following active ingredients: ethyl alcohol, 60% to

95% by volume in an aqueous solution, or isopropyl alcohol, 50% to 91.3% by volume in an

aqueous solution. Ethyl alcohol (ethanol) and isopropyl alcohol (isopropanol) are the

alcoholic solutions most often used as surface disinfectants and antiseptic agents in health

care institutions because they possess many qualities that make them suitable both for

disinfection of equipment and for antisepsis of skin. They are fast acting, minimally toxic to

the skin, nonstaining, and nonallergenic. Alcohols evaporate readily, which is advantageous

for most disinfection and antisepsis procedures. The uptake of alcohol by intact skin and the

lungs when alcohol is used topically is negligible. Alcohols have better wetting properties

than water due to their lower surface tensions, which along with their cleansing and

degreasing actions make alcohols effective skin antiseptics. Alcoholic formulations used to

prepare the skin before invasive procedures should be filtered to ensure that they are free of

spores, or 0.5% hydrogen peroxide should be added (208). Alcohols are also excellent

products for intermediate-level and low-level disinfection of small, clean surfaces,

equipment, and the environment (e.g., rubber stoppers of medication vials, stethoscopes,

and medication preparation areas). Alcohols have some disadvantages. If alcoholic

antiseptics are used repeatedly, they may dry and irritate the skin. Therefore, preparations

for hand disinfection should contain emollients (see the discussion on hand antisepsis in

“Disinfectants for Living Tissue” below). Moreover, alcohols may damage rubber, certain

plastic items, and the shellac mountings of lensed instruments after prolonged and repeated

use (216). Moreover, alcohols are flammable (one should consider the flash point) and thus

must not be used on large surfaces, particularly in closed, poorly ventilated areas. Alcohols

cannot penetrate protein-rich materials. Therefore, a spray or a wipe with alcohol may not

disinfect a surface contaminated with blood or other body fluids that has not been cleaned

first.

The exact mechanism by which alcohols destroy microorganisms is not fully understood. The

most plausible explanation for the antimicrobial action is that alcohols coagulate (denature)

proteins (e.g., enzymatic proteins), impairing specific cellular functions (160). Ethyl and

isopropyl alcohols at appropriate concentrations have broad spectra of antimicrobial activity

that include vegetative bacteria, fungi, and viruses. In fact, their antimicrobial efficacies are

enhanced in the presence of water, with optimal alcohol concentrations being 60 to 90% by

volume.

Alcohols (i.e., 70 to 80% ethyl alcohol) rapidly (i.e., within 10 to 90 s) kill vegetative

bacteria, such as S. aureus, Streptococcus pyogenes, Enterobacteriaceae, and P.

aeruginosa in suspension tests (208). Isopropyl alcohol is slightly more bactericidal than

ethyl alcohol (160) and is highly effective against vancomycin-resistant enterococci (239). It

also has excellent activity against fungi, such as Candida spp., Cryptococcus

neoformans, Blastomyces dermatitidis, Coccidioides immitis, Histoplasma

capsulatum, Aspergillus niger, and dermatophytes and mycobacteria, including M.

tuberculosis. However, alcohols generally do not destroy bacterial spores. In fact, fatal

infections due to Clostridium spp. occurred when alcohol was used to sterilize surgical

instruments. Both ethyl and isopropyl alcohols inactivate most viruses with a lipid envelope

(e.g., influenza virus, herpes simplex virus, and adenovirus). However, several investigators

found that isopropyl alcohol had less virucidal activity against naked, nonenveloped viruses

(216). In the experiments by Klein and DeForest, 2-propanol, even at 95%, could not

inactivate the nonenveloped poliovirus type 1 and coxsackievirus type B in 10 min (151). In

contrast, 70% ethanol inactivated these enteroviruses (151). Neither 70% ethanol nor 45%

2-propanol killed HAV when their activities were assessed on stainless steel disks

contaminated with fecally suspended virus. Among 20 disinfectants tested, only 3 reduced

the titer of HAV by greater than 99.9% in 1 min (2% glutaraldehyde, sodium hypochlorite

with >5,000 ppm free chlorine, and a quaternary ammonium formulation containing 23%

HCl) (176). Bond et al. (34) and Kobayashi et al. (153) demonstrated that 2-propanol (70%

for 10 min) or ethanol (80% for 2 min) made human plasma contaminated with HBV at high

titer noninfectious for susceptible chimpanzees (153). Both 15% ethyl alcohol and 35%

isopropyl alcohol (172) readily inactivate HIV, and 70% ethanol rapidly inactivates high titers

of HIV in suspension, independent of the protein load. However, the rate of inactivation

decreased when virus was dried onto a glass surface and high levels of protein were present

(267). In a suspension test, 40% propanol reduced the rotavirus titer by at least 4 log in 1

min (157) and both 70% propanol and 70% ethanol reduced the release of rotavirus from

contaminated fingertips by 2.7 log units. In comparison, the mean reductions obtained with

liquid soap and an aqueous solution of chlorhexidine gluconate were 0.9 and 0.7 log units,

respectively (15).

Phenolics

Since Lister’s pioneering use of phenol (carbolic acid) as an antiseptic, a large number of

phenol derivatives (or phenolics) have been developed and marketed. Phenol derivatives

originate when one of the hydrogen atoms on an aromatic ring is replaced by a functional

group (e.g., alkyl, benzyl, phenyl, amyl, or chloro). The three phenolics most commonly used

as constituents of disinfectants are o-phenylphenol, o-benzyl-p-chlorophenol, and p-tertamylphenol.

The addition of detergents to the basic formulation results in products that

clean, dissolve proteins, and disinfect in one step. Phenolics at higher concentrations act as

gross protoplasmic poisons, penetrating and disrupting the bacterial cell wall and

precipitating the cell proteins (193). Lower concentrations of these compounds inactivate

cellular enzyme systems and cause essential metabolites to leak from the cell. Phenol

compounds at concentrations of 2 to 5% are generally considered bactericidal,

tuberculocidal, fungicidal, and virucidal against lipophilic viruses (193). However, the

manufacturers’ efficacy claims have generally not been verified by independent laboratories

or the EPA (216). A collaborative study by Rutala and Cole documented the fact that

randomly selected EPA-registered phenolic detergents and quaternary ammonium

compounds do not consistently meet the manufacturers’ bactericidal label claims (218).

Phenolics tested by the AOAC use-dilution method at the recommended use dilution failed to

kill P. aeruginosa in 33 to 78% of laboratories. However, extreme variability of test results

has been observed among laboratories testing identical products (218). Phenolics at in-use

dilutions are not lethal to bacterial spores. Terleckyj and Axler found that a 2% phenolic

killed a wide spectrum of clinically important fungi but did not kill Aspergillus

fumigatus (260). Although 5% phenol inactivated both lipophilic and hydrophilic viruses,

Klein and DeForest found that 12% o-phenylphenol was effective only against lipophilic

viruses (151). Similarly, other investigators demonstrated little or no virucidal effect of a

phenolic against coxsackievirus type B4, echovirus type 11, or poliovirus type 1 (190). Martin

et al. showed that a 0.5% commercial phenolic formulation (2.8% o-phenylphenol and

2.7% o-benzyl-p-chlorophenol) inactivated HIV (172), but another commercial product

containing phenolics at a final concentration of 1% did not completely inactivate cellassociated

HIV suspended in blood (89). A phenol-based preparation (14.7% phenol diluted

1:256 in tap water) and a bleach dilution (800 ppm available chlorine) reduced rotavirus

numbers similarly and interrupted transfer of virus from disks to fingerpads (238). Phenolic

compounds are relatively tolerant of anionic and organic matter. They are absorbed by

rubber and plastics and leave a residual film, which may irritate skin and tissues. p-tert-

Butylphenol and p-tert-amylphenol have been reported to depigment skin. Although

differences between the various compounds exist, phenolics are degraded in wastewater at a

lower rate than other germicides, which limits their use in Europe. Phenolic germicidal

detergent solutions may be used for intermediate-level and low-level disinfection of surgical

instruments and noncritical patient care items. These compounds are also appropriate for

decontaminating the hospital environment, including laboratory surfaces. They should not be

used to disinfect bassinets and incubators because they can cause hyperbilirubinemia in

infants (216).

Quaternary Ammonium Compounds

A wide variety of quaternary ammonium compounds (quats) with antimicrobial activity have

been introduced in the past decade. Some of the compounds used in health care settings are

benzalkonium chloride, alkyldimethylbenzyl ammonium chloride, and didecyldimethyl

ammonium chloride. Quats are cationic surface-active detergents, which appear to kill

microorganisms by disrupting cell membranes, inactivating enzymes, and denaturing cell

proteins (181). However, they have a limited antimicrobial spectrum. Products sold as

hospital disinfectants are not sporicidal and are generally not tuberculocidal or virucidal

against hydrophilic viruses. Scientific investigations using the AOAC use-dilution method

have not reproduced the bactericidal and tuberculocidal claims made by the manufacturers

(219). Consequently, HCWs should be suspicious of the claims on labels and of results from

in-house evaluations that have not been verified by an independent laboratory. The

overestimation of the germicidal activity may be related to incomplete inactivation of the

compounds tested. In this case, the bacteriostatic (inhibitory) activity rather than the

bactericidal activity is measured (181). The antimicrobial spectrum of quats may be

improved by combining them with amines and biguanides or by using them at higher

temperatures in washing machines. Several outbreaks of infections have been associated

with quat solutions contaminated in use by gram-negative bacteria such

asPseudomonas spp. or S. marcescens or by Mycobacterium abscessus (99, 189, 262). The

contaminated solutions were used as antiseptics on skin and tissue and to disinfect patient

care supplies or equipment (i.e., cardiac catheters and cystoscopes). In fact, microbiology

laboratories use the quat cetrimide in selective media to isolate P. aeruginosa. Quats have

other disadvantages. Genes conferring resistance to quats have been detected in 6 to 42%

of S. aureus isolates collected in Japan and Europe (175). Organic matter, anionic detergents

(soaps), and materials such as cotton and gauze pads can reduce the microbicidal activities

of quats. Despite these limitations, quats are nonstaining, odorless, noncorrosive, and

relatively nontoxic. They are excellent cleaning agents, but sticky residue may build up on

surfaces. On the basis of their limited antimicrobial spectra, they should be used in hospitals

only for environmental sanitation of noncritical surfaces such as floors, furniture, and walls

(216).

Other Germicides of Interest

Glucoprotamine, the conversion product of L-glutamic acid and cocopropylene-1,3-diamine,

possesses a broad antimicrobial spectrum that includes vegetative bacteria, mycobacteria,

fungi, and enveloped viruses (85,183). A clinical study examining used specula from a

gynecologic clinic demonstrated that the product killed >6 log units of vegetative bacteria

excluding spores (284). The manufacturer’s data sheets indicate good compatibility of the

compound with humans, the environment, and various materials. A commercial product,

available in Europe, can be used to disinfect instruments and endoscopes.

Peroxygen compounds have proven efficacy against bacteria, bacterial spores, fungi, and a

broad spectrum of viruses. A 1% concentration of a new commercial formulation containing

peroxygen achieved a 105-fold killing of B. subtilis in 2 to 3 h in the absence of blood, but

killing was poor in the presence of blood (67). Moreover, several investigators have found

that peroxygen has poor mycobactericidal activity (45, 116). Besides other applications,

these compounds may be suitable for disinfecting laboratory equipment and workbenches.

Superoxidized water is prepared at the point of use by the electrolysis of NaCl solution,

which generates hypochlorous acid and a mixture of radicals with strong oxidizing properties

(185). Freshly generated solutions rapidly destroy bacteria including spores and

mycobacteria, fungi, and viruses in the absence of organic loading (245). A commercial

adaptation of this process (i.e., Sterilox) has been marketed in Europe since 1999 and

recently was approved by the FDA (see “Endoscopes” below) (185). Because Sterilox

solutions are unstable, they should be used only once for high-level disinfection. Some

investigators have claimed that superoxidized water is compatible with instruments and that

it does not damage the environment, irritate the respiratory tract and skin, or corrode metal.

However, others have reported that superoxidized water damages flexible endoscopes.

Further studies are needed to explore the use of this new disinfectant in clinical settings.

Metals such as copper and silver ions inactivate a wide variety of microorganisms (233).

Although further work is required to explore their use in health care, they currently are used

to disinfect water and to prevent infections associated with medical devices (e.g.,

intravascular catheters impregnated with silver sulfadiazine). For example, copper-silver

ionization systems are successfully used to minimize legionella colonization in water systems

(254). Surfacine is a new silver-based surface germicide that may be applied to inanimate or

animate surfaces. Surfacine immediately eliminates microorganisms from surfaces and also

has long-term residual activity (44, 227). This novel antimicrobial coating might be suitable

for a wide range of applications including the preventing of microbial contamination of

medical devices, if further studies confirm the promising preliminary data.

Specific Issues

Cleaning and Disinfecting Surfaces and Floors

In general, the environment is not a primary reservoir for nosocomial pathogens. However,

in some cases environmental contamination may be important. Recent examples include

respiratory syncytial virus (121) and the SARS coronavirus (106). The CDC’s recent

guidelines for environmental infection control in health care facilities recommend using an

EPA-registered hospital detergent/disinfectant designed for general housekeeping purposes

in patient care areas, especially in intensive care units, operating theaters, and emergency

rooms, where blood, body fluids, or multidrug-resistant organisms may have contaminated

surfaces (243). A one-step process is adequate in most areas, but a rinse step is necessary

in nurseries and neonatal intensive care units, especially if a phenolic agent was used (294).

Products with quats allow cleaning and disinfecting in one step, but residual quats on the

surface may result in sticky, smeary surfaces. Other products may require a two- step

approach (a cleaning step and a disinfection step), doubling the workload. “High-touch”

surfaces (e.g., doorknobs, bed rails, and light switches) should be disinfected more

frequently than “minimal-touch” surfaces. A simple detergent is adequate for cleaning

surfaces for other patient care areas and in non-patient care areas. Cleaning with a

detergent is much more important than adding a disinfectant to the solution. In fact, several

studies found that adding a disinfectant did not prolong the reduction in bacterial load on

surfaces (83). Routine disinfection of environmental surfaces is necessary for all areas with

patients in contact isolation (e.g., patients infected with methicillin-resistant S.

aureus [MRSA]). Twice-daily disinfection is necessary to control an outbreak with

vancomycin-intermediate S. aureus (78, 178).

In rare situations, routine disinfection of surfaces and floors is crucial: when cases of

norovirus or clusters with C. difficile or MRSA are detected, an immediate switch from

cleaning floors and surfaces to using a highly active disinfectant is warranted. Several

studies demonstrate a correlation between contaminated surfaces and clinical cases

(66, 75, 150). When patients with suspected norovirus infection vomit, immediate

disinfection of the vomitus with highly concentrated bleach or an oxygen-release compound

is crucial. Norovirus is highly contagious; in fact, 100 virions are sufficient to induce

infection, but >106 virions are shed by infected patients.

Emergence of Resistance to Biocides

Microorganisms rarely become resistant to disinfectants. However, frequent use of sublethal

concentrations of disinfectants can select for resistant strains (17, 36, 271). Mechanisms of

resistance include acquisition of resistance plasmids, changes in the cell membrane (e.g.,

chlorhexidine in Psuedomonas stutzeri), capsule formation (Klebsiella spp.), and activation of

the norA efflux pump (S. aureus). A large proportion of household soaps now contain

antibacterial agents (up to 45% in one study), which may increase the probability that

resistant bacteria will emerge (197). Multiple outbreaks have been associated with soaps

containing antibacterial agents such as chlorhexidine, hexetidine solution, or chlorxylenol

(17, 36, 271). However, the concentrations of biocides used in the health care setting are

much higher than the minimum biocidal concentrations in vitro. Therefore, resistance has not

become a major problem in the clinical setting to date. Readers desiring more information

about disinfectants and antiseptics (33, 98) and resistance to these agents should read

several excellent articles (33, 98, 167, 244).

Inactivation of Emerging Pathogens and Antibiotic-Resistant Bacteria

New and emerging pathogens such as the causative agent of vCJD, noroviruses, SARS

coronavirus, avian and swine influenza viruses, hypervirulent C. difficile, Panton- Valentine

leukocidin-producing S. aureus, gram-negative rods producing extended-spectrum β-

lactamases or metallo-β- lactamases, or Klebsiella pneumoniae producing carba penemases

threaten the public health. Only limited data exist regarding the susceptibility of emerging

pathogens to commonly used disinfectants or sterilants. Surrogate microbes have been

studied for some pathogens. Examples include feline calicivirus for noroviruses, vaccinia

virus for variola virus, and Bacillus atrophaeus (formerly B. subtilis) for B. anthracis (278).

Other infectious agents that cannot be evaluated by standard testing procedures (e.g.,

hepatitis C virus [HCV]) have been tested by alternative methods, such as PCR. With the

exception of prions, there is no evidence that emerging pathogens are less susceptible to

approved standard disinfection and sterilization procedures than are comparable classical

pathogens. Standard disinfection and sterilization procedures for patient care equipment as

recommended in guidelines and in this chapter are adequate to disinfect or sterilize

instruments or devices contaminated with blood and other body fluids (228). Hospital

disinfectants registered by the EPA, other than one peroxygen compound, do not have

specific claims for activity against noroviruses. Because noroviruses are nonenveloped, most

quats do not have significant activity against them. Phenolic-based preparations have been

found to be active in vitro against a surrogate virus of this group. However, concentrations

two- to four-fold higher than those recommended for routine use by manufacturers may be

required. In the event of a norovirus outbreak, the CDC recommends using a hypochlorite

solution (minimum concentration of 1,000 ppm chlorine) to decontaminate hard, nonporous,

environmental surfaces (http://www.cdc.gov /ncidod/dhqp/id_norovirusFS.html). SARS

coronavirus and avian influenza virus are inactivated by sodium hypochlorite and a

commercially available peroxygen compound (158); phenolic compounds and quats are less

effective. A sporicidal germicide is required to efficiently eliminate C. difficilespores. In a

recent study, glutaraldehyde (2%), peracetyl ions (1.6%, equivalent to 0.26% peracetic

acid), and acidified nitrite demonstrated biocidal activity against C. difficile spores (293).

Hypochlorite-based disinfectants have been used, with some success, to disinfect

environmental surfaces in areas with ongoing transmission of C. difficile. Recent outbreaks

with virulent strains may require more focus on environmental cleaning and disinfection

(95, 178). There are no data demonstrating that disinfectants used at recommended contact

conditions and concentrations are less effective against antimicrobial-resistant bacteria than

against antimicrobial-susceptible bacteria (228). Inactivation of prions, including those

causing vCJD, is discussed below.

Decontamination in the Event of Biological Terrorism

If a biological agent is released, environmental decontamination measures may be necessary

to decrease the risk of spreading of the disease. A decontamination agent should be effective

against possible pathogens and readily available at reasonable cost. Therefore, sodium

hypochlorite (household bleach) is usually recommended, especially if bacterial spores are

involved. This agent is well suited for various decontamination procedures in the laboratory

and health care setting. In addition, it may be used to decontaminate protective equipment

and clothing worn by first responders and decontamination workers. Smallpox virus does not

survive long in the environment but may remain viable for extended periods under favorable

conditions. CDC guidelines recommend incinerating items that are not needed or cannot be

decontaminated, sterilizing items in an autoclave or an ethylene oxide sterilizer,

decontaminating spaces and rooms with vaporized paraformaldehyde (or use of an Amphyl

fogger), and soaking equipment or wiping down surfaces with a 5% aqueous solution of a

phenolic germicidal detergent (http://www.bt.cdc.gov/agent /smallpox/responseplan/

index.asp#guidef). Since contaminated clothing can spread the virus to personnel, bed

linens and clothes must be autoclaved or laundered in hot water supplemented with bleach

(128). Other disinfectants that are used for standard hospital infection control, such as

sodium hypochlorite and quaternary ammonium compounds, are also effective to

decontaminate surfaces (128). Only vaccinated personnel should perform the

decontamination procedures. B. anthracis spores are extremely stable and can remain viable

for decades in the environment (138). The CDC recommends that laboratory staff use a

1:10-diluted hypochlorite solution when addressing spills, items, and surfaces contaminated

with B. anthracis(http://www.bt.cdc.gov/agent/anthrax/infection-control/). Decontamination

of a building or of large areas contaminated with anthrax spores is extremely difficult. Spotts

et al. summarized the literature on inactivation of B. anthracis spores (250). C.

botulinum and its spores are killed by a 1:10 dilution of sodium hypochlorite. Heat (≥85°C

for 5 min) or 0.1 M sodium hydroxide (contact time, 20 min) inactivates the toxin (18).

Persons with direct exposure to powder or liquid aerosols containing Francisella

tularensis should wash their body and clothing with soapy water (79). In the circumstances

of a laboratory spill or intentional release, environmental surfaces can be decontaminated

with a 1:10-diluted hypochlorite solution. After 10 min, a 70% alcohol solution can be used

to further clean the area and reduce the corrosive action of the bleach (79). Yersinia

pestis does not survive long outside the host. The WHO estimated that a plague aerosol

would be effective and infectious for 1 h. Thus, areas exposed to aerosols of Y. pestis do not

need to be decontaminated (137). Equipment or environmental surfaces contaminated with

the agents causing Ebola hemorrhagic fever, Marburg hemorrhagic fever (Filoviridae), Lassa

fever, and related infections (Arenaviridae and Bunyaviridae) should be disinfected with a

suitable registered hospital disinfectant or a 1:100 dilution of a hypochlorite solution.

Surfaces grossly soiled with vomitus or stool should be disinfected with a 1:10 dilution. If

possible, serum used for laboratory tests should be pretreated with heat inactivation at 56°C

and polyethylene glycol p-tert-octylphenyl ether (Triton X-100). Treatment with 10 μl of 10%

Triton X-100 per ml of serum for 1 h reduces the titer of hemorrhagic fever viruses in serum.

If treatment with Triton X-100 is not feasible, heat inactivation alone may reduce infectivity

somewhat (52). Medical, public health, and laboratory responses to the release of organisms

or toxins that pose a risk to national security, i.e., variola major virus (smallpox), Bacillus

anthracis, Clostridium botulinum toxin, Francisella tularensis, Yersinia pestis, and certain

filoviruses and arenaviruses are discussed in chapter 10 of this Manual and in numerous

publications (18, 79, 128, 137, 138). The CDC published guidelines for the management of

patients with suspected viral hemorrhagic fever (52) and recently posted updated guidelines

atwww.cdc.gov/ncidod/hip/BLOOD/VHFinterimGuidance05_19_05.pdf.

Endoscopes

Reprocessing endoscopes is probably the most challenging reprocessing task in health care.

Multiple reports of outbreaks associated with insufficient reprocessing techniques or defects

of the endoscope have been published (Table 7). However, ample data indicate that a

sufficient level of safety can be achieved even with manual disinfection of endoscopes if the

guidelines are strictly followed (173). Today, endoscopes are involved in transmission of

infectious diseases in less than 1 of 106 Mio endoscopies. Flexible endoscopes have intricate,

sophisticated small parts that are difficult to clean but must be cleaned before they can be

disinfected because organic material such as blood, feces, and respiratory secretions

interfere with disinfection (71). Several studies have demonstrated the importance of

cleaning in experimental studies with duck HBV, HIV, and Helicobacter pylori, (82, 292). A

large study in several centers in the United States found that 23.9% of the cultures of

specimens from the internal channels of 71 gastrointestinal reprocessed endoscopes grew

≥106 CFU of bacteria and that 78% of the facilities did not sterilize all biopsy forceps (144).

Other studies have documented that up to 40% of the institutions do not follow published

guidelines for endoscope disinfection (12, 92, 113) and reuse of disposable endoscopic

accessories is common in the United States. These items frequently are not sterilized, and

reprocessing protocols are not standardized. Therefore, reused disposable items might be a

source of cross- transmission (63, 71). Currently, most high-level disinfectants approved by

the FDA for reprocessing endoscopes contain >2% aldehyde with or without peracetic acid

(http://www.fda.gov/cdrh/ode/germlab.html). However, aldehydes should only be used after

completing the cleaning cycle because they may stain prions to the instruments. Endoscopes,

which are semicritical items, must be immersed in ≥2% glutaraldehyde for ≥20 min to

achieve the necessary level of disinfection. These parameters are sufficient to kill ≥3 log

units of mycobacteria, the most resistant vegetative bacteria. Glutaraldehyde-resistant

mycobacteria have been identified (116). Several authors raised concerns that C.

difficile may not be fully inactivated by standard reprocessing procedures. However,

transmission of C. difficile by contaminated endoscopes has not been reported to date.

Moreover, cryptosporidia withstand several hours of exposure to glutaraldehyde (290) but do

not survive on dry surfaces (206). Therefore, drying before storing reprocessed items is part

of the process and should not be cut to save time, e.g., in endoscopy units. The

glutaraldehyde concentration in commercial cleaner-disinfectors can decrease by more than

50% after 2 weeks, which may promote the emergence of resistant bacteria (269). Higher

concentrations of glutaraldehyde (3.2% instead of 2%) appear to be safe for endoscopes and

achieve the required ≥3-log-unit killing with a higher margin of safety than achieved with the

standard concentration (7). OPA and peracetic acid plus hydrogen peroxide can be used to

disinfect endoscopes. Because the latter might corrode some endoscopes, reprocessing staff

should ensure that the manufacturer of the endoscope approves this disinfectant for

reprocessing. Automated washer-disinfectors specifically for endoscopes were developed, in

part, to reduce the work needed to reprocess endoscopes and to decrease the risk of human

errors during manual reprocessing. These machines rinse the endoscopes, clean them in

several steps, and run a full-cycle disinfection process. The time endoscopes are exposed to

disinfectants is set by the machine and cannot be shortened, as it can be by busy staff

manually reprocessing endoscopes. However, endoscope washers can become contaminated

with pathogenic bacteria. For example, one study found gram-negative bacteria and/or

mycobacteria in 27% of cultures of specimens obtained before the final alcohol rinse and in

10% of cultures of specimens obtained thereafter. In the same study, 37 and 27% of the

manually disinfected endoscopes remained contaminated at the same time points (101). In

1992, Olympus recalled (recall no. Z-039/040-2 by the FDA) its 835 model endoscope

washers because the design allowed the internal tanks and tubing to become colonized by

waterborne organisms such as Pseudomonas spp. In 1999, CDC reported three outbreaks

related to the Steris System 1 (53). This device is supposed to sterilize the endoscopes, but

they must first be cleaned manually (42). See Table 7 for a summary of outbreaks related to

endoscopes, including those related to contaminated washer-disinfectors. Newer washerdisinfectors

should continuously monitor the pressure in all channels to detect debris

blocking the channels, provide adapters for all types of endoscopes, use an appropriate

disinfection process with an FDA-approved disinfectant, use filtered water or sterile water for

rinsing, and have a built-in automatic disinfection process. These washer-disinfectors can

help staff trace problems by monitoring and documenting the disinfecting process in a

manner similar to that used by autoclaves. To avoid problems, knowledgeable staff should

review currently marketed machines before purchasing a washer-disinfector to ensure that

the one they choose is appropriate for their needs (21). To facilitate this process, the FDA

recommends that the manufacturer provide a list of all brands and models of endoscopes

that are compatible with the washer-disinfector and highlight limitations associated with

processing of certain brands and models of endoscopes and accessories. Preferably, the

manufacturer should identify endoscopes and accessories that cannot be reliably reprocessed

in the device (negative list). In addition, HCWs should be trained to use the equipment and

monitored subsequently to ensure that they follow the protocol exactly. Although this is not

yet mandatory, it is prudent to regularly culture the rinse water of washer-disinfectors for

pathogens such as Pseudomonas spp. and Mycobacterium spp. to identify problems before

clinical cases occur. In Europe, validation of the whole procedure is necessary to ensure that

it complies with the requirements of the European Standard EN ISO 15883 parts 1, 4, and 5

for automated endoscope reprocessing (23). However, outbreaks may occur despite negative

routine culture results (206, 290).

Common Antiseptic Compounds

Alcoholic Compounds

The reader is referred to the section above on alcohols. As outlined above, alcohol is the

most important skin disinfectant. Alcohols used for skin disinfection prior to invasive

procedures should generally be free of spores to avoid any contamination. Although the risk

of infection is minimal, the low additional cost for a spore-free product is justified. One study

indicated that alcohol may result in dermal absorption of isopropyl alcohol from a commercial

hand rub, which may interfere with religious beliefs of HCWs (264). However, the WHO

resolved this issue in their most recent guidelines published in 2009, and Muslims, for

example, are allowed to use alcoholic compounds for hand hygiene.

Chlorhexidine

Chlorhexidine gluconate, a cationic bisbiguanide, has been widely recognized as an effective

and safe antiseptic for nearly 40 years (80, 204). Chlorhexidine formulations are extensively

used for surgical and hygienic hand disinfection (see previous discussion). Other applications

include preoperative showers (or whole-body disinfection), antisepsis in obstetrics and

gynecology, management of burns, wound antisepsis, and prevention and treatment of oral

disease (plaque control, pre- and postoperative mouthwash, and oral hygiene) (80, 204).

When chlorhexidine is used orally, its bitter taste must be masked and it can stain the teeth.

Intravenous catheters coated with chlorhexidine and silver sulfadiazine are used to prevent

catheter-associated bloodstream infections (169). In fact, an infection control program to

prevent catheter-associated bloodstream infections included hand hygiene, chlorhexidine site

care, and full-barrier precautions in a large clinical study in intensive care units: these

interventions led to an infection rate close to zero (201). Today, chlorhexidine compounds

are considered the gold standard for catheter site care (186). Chlorhexidine is most

commonly formulated as a 4% aqueous solution in a detergent base. However, alcoholic

preparations have been demonstrated in numerous studies to have better antimicrobial

activity than detergent-based formulations (161). Bactericidal concentrations destroy the

bacterial cell membrane, causing cellular constituents to leak out of the cell and cell contents

to coagulate (80). Chlorhexidine gluconate bactericidal activity against vegetative grampositive

and gram-negative bacteria is intermediately rapid. In addition, it provides a

persistent antimicrobial action that prevents the regrowth of microorganisms for up to 6 h.

This effect is desirable when a sustained reduction in the microbiota reduces infection risk

(e.g., during surgical procedures). Chlorhexidine has little activity against bacterial and

fungal spores except at high temperatures. Mycobacteria are inhibited but are not killed by

aqueous solutions. Yeasts and dermatophytes are usually susceptible, although the fungicidal

action varies with the species (79). Chlorhexidine is effective against lipophilic viruses (e.g.,

HIV, influenza virus, and herpes simplex virus types 1 and 2), but viruses such as poliovirus,

coxsackievirus, and rotavirus are not inactivated (80). Unlike what occurs with povidone

iodine, blood and other organic materials do not affect the antimicrobial activity of

chlorhexidine significantly (165). However, inorganic anions and organic anions such as

soaps are incompatible with chlorhexidine and its activity is reduced at extreme acidic or

alkaline pH and in the presence of anionic- and nonionic-based moisturizers and detergents.

Microorganisms can contaminate chlorhexidine solutions (194) and resistant isolates have

been identified. For example, Stickler found chlorhexidine-resistant Proteus mirabilis after

chlorhexidine was used extensively over a long period to prepare patients for bladder

catheterization (252). The chlorhexidine resistance among vegetative bacteria was thought

to be limited to certain gram-negative bacilli (such as P. aeruginosa,

Burkholderia [Pseudomonas] cepacia, P. mirabilis, and S. marcescens) (253). However,

genes conferring resistance to various organic cations, including chlorhexidine, have been

identified in S. aureus clinical isolates (175, 188). Chlorhexidine has several other

limitations. When absorbed onto cotton and other fabrics, it usually resists removal by

washing. If a hypochlorite (bleach) is used during the washing procedure, a brown stain may

develop (80). Long-term experience with the use of chlorhexidine has demonstrated that the

incidence of hypersensitivity and skin irritation is low. However, severe allergic reactions

including anaphylaxis have been reported (90, 295). Although cytotoxicity has been

observed in exposed fibroblasts, no deleterious effects on wound healing have been

demonstrated in vivo. There is no evidence that chlorhexidine gluconate is toxic if it is

absorbed through the skin, but ototoxicity can occur when chlorhexidine is instilled into the

middle ear during operative procedures. High concentrations of chlorhexidine and

preparations containing other compounds (e.g., alcohols and surfactants) may damage eyes

(257).

Iodophors

Iodophors essentially have replaced aqueous iodine and tincture as antiseptics. Iodophors

are chemical complexes of iodine bound to a carrier such as PVP or ethoxylated nonionic

detergents (poloxamers). These complexes gradually release small amounts of free

microbicidal iodine. The most commonly used iodophor is PVP iodine. Its preparations

generally contain 1 to 10% PVP iodine, which is equivalent to 0.1 to 1.0% available iodine.

The active component appears to be free molecular iodine (I2). A paradoxical effect of

dilution on the activity of PVP iodine has been observed. As the dilution increases,

bactericidal activity increases up to a maximum and then falls (114). Commercial PVP iodine

solutions at dilutions of 1:2 to 1:100 kill S. aureus and Mycobacterium chelonae more rapidly

than do stock solutions (27). S. aureus can survive a 2-min exposure to full-strength PVP

iodine solution but cannot survive a 15-s exposure to a 1:100 dilution of the iodophor (27).

Thus, iodophors must be used at the dilution stated by the manufacturer. The exact

mechanism by which iodine destroys microorganisms is not known. Iodine may react with

microorganisms’ amino acids and fatty acids, destroying cell structures and enzymes (114).

Depending on the concentration of free iodine and other factors, iodophors exhibit a broad

range of microbicidal activity. Commercial preparations are bactericidal, mycobactericidal,

fungicidal, and virucidal but not sporicidal at the dilutions recommended for use. Prolonged

contact times are required to inactivate certain fungi and bacterial spores (216). Despite

their bactericidal activity, PVP iodine and poloxamer-iodine solutions can become

contaminated with B. (P.) cepacia or P. aeruginosa, and contaminated solutions have caused

outbreaks of pseudobacteremia and peritonitis (28, 72). In fact, B. cepacia was found to

survive for up to 68 weeks in a PVP iodine antiseptic solution (13). The most likely

explanation for the prolonged survival of these microorganisms in iodophor solutions is that

organic or inorganic material and biofilm may mechanically protect the microorganisms.

Iodophors are widely used for antisepsis of skin, mucous membranes, and wounds. A 2.5%

ophthalmic solution of PVP iodine is more effective and less toxic than silver nitrate or

erythromycin ointment when used as prophylaxis against neonatal conjunctivitis (ophthalmia

neonatorum) (139). In some countries, PVP iodine alcoholic solutions are used extensively

for skin antisepsis before invasive procedures (16). Iodophors containing higher

concentrations of free iodine may be used to disinfect medical equipment. Solutions designed

for use on the skin should not be used to disinfect hard surfaces because the concentrations

of the antiseptic solutions are usually too low for this purpose (216). The risk of side effects,

such as staining, tissue irritation, and resorption, is lower for iodophors than for aqueous

iodine. Iodophors do not corrode metal surfaces (114). However, a body surface treated with

an iodine or iodophor solution may absorb free iodine. Consequently, increased serum iodine

levels (and serum iodide levels) have been found in patients, especially when large areas

were treated for a long period (114). For this reason, hyperthyroidism and other disorders of

thyroid functions are contraindications for the use of iodine-containing preparations.

Likewise, iodophors should not be applied to pregnant and nursing women or to newborns

and infants (50). Because severe local and systemic allergic reactions have been observed,

iodophors and iodine should not be used in patients with allergies to these preparations

(274). Iodophores have little if any residual effect. However, for a limited time they may

have residual bactericidal activity on the skin surface, because free iodine diffuses into deep

regions but also back to the skin surface (114). The antimicrobial efficacy of iodophors is

reduced in the presence of organic material such as blood.

Triclosan and PCMX

Triclosan (Irgasan DP-300 or Irgacare MP) has been used for more than 30 years in a wide

array of skin care products, including hand washes, surgical scrubs, and consumer products.

A review of its effectiveness and safety in health care settings has been published (141). A

concentration of 1% has good activity against gram-positive bacteria, including antibioticresistant

strains, but less activity against gram-negative organisms, mycobacteria, and fungi.

Limited data suggest that triclosan has a relatively broad antiviral spectrum, with high-level

activity against enveloped viruses, such as HIV type 1, influenza A virus, and herpes simplex

virus type 1. However, the nonenveloped viruses proved more difficult to inactivate. Clinical

strains with low-level resistance to triclosan have been identified, but the clinical significance

of this remains unknown (255). Triclosan is added to various soaps, lotions, deodorants,

toothpastes, mouth rinses, commonly used household fabrics, plastics, and medical devices.

Moreover, the mechanisms of triclosan resistance may be similar to those involved in

antimicrobial resistance (6) and some of these mechanisms may account for the observed

cross-resistance of laboratory isolates to antimicrobial agents (65). Consequently, concerns

have been raised that widespread use of triclosan formulations in non-health care settings

and products may select for biocide resistance and even cross-resistance to antibiotics.

However, environmental surveys have not demonstrated an association between triclosan

usage and antibiotic resistance (214). Triclosan solutions produce a sustained residual effect

against resident and transient microbiotas, which is minimally affected by organic matter.

Numerous studies have not identified toxic, allergenic, mutagenic, or carcinogenic potential.

Triclosan formulations may help control outbreaks of MRSA when used for hand hygiene and

as a bathing cleanser for patients (141). However, some MRSA isolates have reduced

triclosan susceptibility. Triclosan formulations are less effective than 2 to 4% chlorhexidine

gluconate when used for surgical scrub solutions; properly formulated triclosan solutions may

be used for hygienic hand washing. PCMX (chloroxylenol) is an antimicrobial used in handwashing

products. It is available at concentrations of 0.5 to 3.75%. Its properties are similar

to those of triclosan. Nonionic surfactants may neutralize PCMX.

Octenidine

Octenidine dihydrochloride is a novel bispyridine compound which is an effective and safe

antiseptic agent. The 0.1% commercial formulation favorably compared with other

antiseptics with respect to antimicrobial activity and toxicological properties. In vitro and in

vivo it rapidly killed both gram-positive and gram-negative bacteria as well as fungi

(110, 242). Octenidine is virucidal against HIV, HBV, and herpes simplex virus. Similar to

chlorhexidine, it has a marked residual effect. No toxicological problems have been found

when the 0.1% formulation was applied according to the manufacturer’s recommendations.

The colorless solution is a useful antiseptic for mucous membranes of the female and male

genitals and the oral cavity (24), but its bad taste limits its use orally. In a recent

observational study, the 0.1% formulation was highly effective and well tolerated for the

care of central venous catheter insertion sites (261). The results of this study have also been

supported by a randomized controlled clinical trial (81). Octenidine is not registered for use

in the United States.

STERILIZATION Back to top

Principles, Definitions, and Terms

As outlined in Table 3, sterilization is not a relative term but defines the complete absence of

any viable microorganisms including spores. However, this absence cannot be proved by

current microbiological techniques (142). Therefore, sterilization can be defined as a closely

monitored, validated process used to render a product free of all forms of viable

microorganisms, including all bacterial endospores. To test the ability of sterilization systems

to meet the latter definition of sterilization, manufacturers developed a worst-case scenario

that allows the process (log killing) to be quantified and estimates the probability of process

failure. Large safety margins were included in this test, which is based on the assumption

that items are heavily contaminated with spores, soil, and proteins. It is important to note

that while these conditions are used for the testing, in clinical practice items that are heavily

soiled should not be sterilized and such a scenario would represent a critical failure of the

reprocessing cycle. Any device undergoing sterilization first must undergo an appropriate

cleaning process. A manufacturer must demonstrate that a sterilizer is effective against a

wide range of clinically important microorganisms before being approved by the FDA. In

addition, proof of efficacy must be performed with organisms (usually bacterial spores) that

have been shown to be the most resistant to the new technology. A validated and reliable

biological indicator must be developed, and studies must establish that sterility will be

consistently achieved when critical process parameters operate within a defined range. This

assures the operator that as long as there is no operational error or equipment failure,

sterility is achieved. Several guidelines are essential documents for staff needing to

understand reprocessing and sterilization of medical devices. ISO 14937 provides general

criteria for characterizing a sterilizing agent and for the development, validation, and routine

control of a sterilization process for medical devices. ISO 11134 (moist heat) and ISO 11135

(ethylene oxide) documents describe the standards for use of these methods of sterilization

in the industrial setting in the United States. The American National Standard

Institute/Association for the Advancement of Medical Instrumentation (ANSI/AAMI) published

adaptations of these standards for health care facilities: Standard 46 (moist heat) and

Standard 41 (ethylene oxide) (Table 3). In Europe, EN 550, EN 554, and EN 285 define the

standards for steam and ethylene oxide sterilization. ISO 14161 provides guidance that staff

can use when selecting and using biological indicators and when interpreting the results of

these tests. ISO 17664 specifies which information medical device manufacturers must

provide so that the medical device can be processed safely and continue to function properly.

Readers are referred to other publications for additional information about sterilization

(33, 115, 142). Hot-air sterilization does not belong to the state-of-the-art technologies, but

it is still used in many countries. However, the distribution of dry heat to the instruments

requires long exposure times. Temperatures of >185°C resinify paraffin, destroying the

lubricating function of instruments, and higher temperatures are corrosive, resulting in loss

of hardness. Therefore, hot-air sterilization has largely been replaced by better, safer, and

faster technologies.

Monitoring

Any sterilization process must be monitored by mechanical, physical, chemical, and

facultatively biological methods. Before routine use, the performance of the machine should

be validated with the most difficult load used at the institution to ensure safety of the

process. In addition, a printout of the physical parameters (e.g., temperature and pressure)

during sterilization should be kept for documentation purposes. In addition, chemical

indicators placed on the tested items change color if they are exposed to adequate

temperatures and exposure times. They are inexpensive and easy to use and provide a

visual indication that the item has been exposed to the sterilization process. Good clinical

indicators are able to identify a sterilizer failure. However, some are too sensitive, giving

false-positive results (220, 223), which may cause unnecessary recalls of adequately

sterilized items. Less sensitive chemical indicators do not detect small deviations in the

process. In 1963 Bowie and Dick determined that if residual air remained in a sterilizer after

the vacuum phase and there was only one package in the chamber, the air would

concentrate in that package (38). They developed the Bowie-Dick test to determine whether

steam penetration and air removal occurred successfully. This test does not provide

information about the sterilization process.

Biological indicators are the best monitors of the sterilization process. If the spores in

commercially available standard biological indicators do not grow during an appropriate

incubation period, the results indicate that the process was able to kill ≥106 CFU. For flash

sterilization, the Attest Rapid Readout biological indicator detects the presence of a sporeassociated

enzyme, α-D-glucosidase, and permits staff to assess the efficacy of sterilization

within 60 min (270). Staff should investigate positive biologicals because they can provide

the only indication that something is wrong with the sterilization process (51).

An important question is whether a load can be distributed before the final results of the

biological indicator are available (i.e., parametric release). The Joint Commission on

Accreditation of Healthcare Organizations standard allows the use of appropriate chemical

indicators without routine use of a biological indicator. A common approach is to use the

sterilized items if the physical and chemical parameters of adequate sterilization were met

without awaiting the culture results from the biological indicators. In Europe, routine use of

biological indicators is not required if the sterilizer has undergone testing by a validation

procedure used for industrial steam sterilization (EN 285, EN 550, EN 554, or EN 556). Most

sterilizers in European hospitals probably do not meet these very strict requirements (268),

and consequently, biological indicators are used regularly to ensure that they are working

properly. These industrial standards for validation of steam sterilization will be implemented

in health care organizations, but this change is controversial because of the associated

expenses. The future is likely to involve parametric release with regular validation and/or

commissions of the equipment. Legal aspects will probably determine the outcome of this

discussion, and lawyers are likely to accept nothing but a zero risk. However, the goal of a

zero risk for contamination in central sterilization services will probably contribute to

excessive health care costs. Therefore, standards for sterilization should exclude a risk for

contamination after the reprocessing cycle but should avoid steps that are performed only for

legal reasons.

Packaging, Loading, and Storage

Items that are clean and dry should be inspected and then wrapped and packaged (or put in

containers) before sterilization. Wrappers should allow steam or gas to penetrate into the

package but should protect the items from recontamination after sterilization. For steam

sterilization, muslin as the only wrapper has limitations and handling of items made of

muslin leads to contamination (286). Items should be labeled with information such as

expiration date, type of sterilization, and identification code for traceability.

Steam Sterilization

The most reliable method of sterilization is one that uses saturated steam under pressure. It

is inexpensive, nontoxic, and very reliable.

Steam penetrates fabrics, and its inherent safety margin is much higher than that of any

other sterilization technique. Therefore, it should be used whenever possible. Obviously,

other techniques must be used for heat-sensitive items. Steam irreversibly coagulates and

causes denaturation of microbial enzymes and proteins. Three parameters are critical to

ensure that steam sterilization is effective: the amount of time the items are exposed to

steam, the temperature of the process, and moisture. Unlike time and temperature, the

moisture condition in the autoclave cannot be directly determined. The D-value determines

the time required to kill 106 CFU of the spores most resistant to the sterilization process

under study. Devices or instruments must reach the desired temperature, which is not

necessarily identical to the temperature displayed on the autoclave’s gauge. A drop of only

1.7°C (3°F) increases the time required to sterilize an item by 48%. Without moisture, a

temperature of 160°C is required for dry-heat sterilization. Dry air does not provide steam

for condensation, and the heat transfer to objects is slower than when moisture is present.

Pressurized steam quickly transfers energy to the sterilizer load and causes more rapid

denaturation and coagulation of microbial proteins. In addition, pressurizing the steam allows

one to achieve dry 100% saturated steam. Thus, there is no mist that could cause the

packaging and/or the items to become wet.

Residual air in the autoclave interferes with the sterilization process. The amount of air

within the sterilizer can be estimated by comparing the chamber pressure with the saturated

steam pressure calculated from the average chamber temperature. A measured pressure

greater than the calculated saturated pressure indicates the presence of residual air in the

chamber. Such monitoring devices are common in the United Kingdom.

Several types of autoclaves are available: gravity displacement steam sterilization,

prevacuum steam sterilization, and steam flash-pressure pulsing steam sterilization

autoclaves. The sterilization process is less consistent in gravity displacement steam

sterilizers than in the other sterilizers (73). For example, gravity displacement autoclaves are

more likely than the other systems to leave residual air in the chamber before the steam is

introduced. Prevacuum sterilizers resolved part of this problem and cut the cycle time in half.

However, the effectiveness of sterilization still can be compromised by small leaks (1 to 10

mm Hg/min) in the sterilizer (142). The most current technology is the steam flash-pressure

pulsing steam sterilization technique because air leaks do not decrease the effectiveness of

the process, it nearly eliminates the problem of air in the chamber, and it reduces the

thermal lag upon heating of the load to the desired exposure temperature (73).

The process of sterilization has several cycles: conditioning, exposure, and drying. Common

cycles for steam sterilization in prevacuum or flash-pressure pulsing steam sterilizers are

121°C for 15 min (121°C for 30 min in a gravity displacement sterilizer) or 132°C for 4 min.

EN 554 requires steam sterilizers to provide this temperature throughout the entire chamber

within a narrow margin (0 to +3°C).

Flash sterilization is an emergency process used, for example, after a surgical instrument is

dropped but needs to be immediately available during a procedure (168). Unwrapped devices

are exposed to pressurized steam for 3 min, usually in the operating suite, sometimes

without a biological indicator. The autoclaves employed are gravity displacement sterilizers

that have the problems mentioned above. If HCWs are in a hurry, they may not clean the

item properly, which will prevent proper sterilization. In addition, because the items are not

wrapped, they can be contaminated easily when they are transported to the operating room.

Even properly wrapped sterile items can become contaminated if they are transported

several times (286). Moreover, some patients have been injured by items that were flash

sterilized (230). Therefore, flash sterilization is controversial and several investigators have

suggested that it should be used only in emergency situations when no other device is

available. Flash sterilization should not replace standard sterilization protocols (93) and

should not be used to save time instead of sterilizing items by the standard methods or

because the health care facility does not want to purchase an extra instrument set (170).

Flash sterilization also means there is a lack of any written documentation, rendering futile

any tracing in cases where something went wrong.

Ethylene Oxide Gas

Temperature- and/or pressure-sensitive items have been sterilized traditionally with ethylene

oxide in a standard gas. Ethylene oxide inactivates all microorganisms, including spores,

probably by an alkylation process. B. subtilis bacterial spores are among the most resistant,

and therefore, these are used as a biological monitor for this process. A new rapid-readout

ethylene oxide biological indicator indicates an ethylene oxide sterilization process failure by

producing fluorescence, which is detected in an autoreader within 4 h of incubation at 37°C,

and a color change related to a change in pH of the growth media within 96 h of continued

incubation (227).

The process of sterilizing items with ethylene oxide begins by adding nitrogen gas to remove

air or by evacuating the chamber. Items are then exposed to ethylene oxide at 55°C

(130°F). Six variable but interdependent parameters—gas concentration, vacuum, pressure,

temperature, relative humidity, and time of exposure—must be controlled when ethylene

oxide is used. The gas concentration cannot be measured online, limiting the extent of

monitoring. Therefore, the concentration should be validated as outlined in ISO 11135.

Ethylene oxide sterilization has several disadvantages. It is useful only as a surface sterilizer

because it does not reach blocked-off surfaces. In addition, ethylene oxide is flammable,

explosive, and carcinogenic to laboratory animals, and it requires special safety precautions.

Moreover, items sterilized by ethylene oxide must be aerated for approximately 12 h to

remove any traces of the gas. Thus, the entire process takes >16 h, but modern sterilizers

can run at shorter cycles. Furthermore, toxic residues can be trapped in the wrapper or the

items. Polyvinyl chloride and polyurethane absorb ethylene oxide readily and require long

periods to dissipate the oxide. The wrapper should be a barrier against recontamination after

sterilization, but it also can prevent ethylene oxide from reaching the item. Therefore, only

materials with documented ethylene oxide penetration and dissipation properties should be

used as wrappers.

The future of ethylene oxide in sterilization is limited, mainly due to its toxicity. However, no

currently available technology, including plasma sterilization (see below), can replace

sterilization with ethylene oxide entirely. In addition, sterilization with ethylene oxide does

not fail as frequently as sterilization with plasma when residual proteins and/or salts are

present on the items (11).

Plasma Sterilization

The low-temperature plasma is produced in a closed chamber with deep vacuum, an

electromagnetic field, and a chemical precursor (hydrogen peroxide or a mixture of hydrogen

peroxide and peracetic acid). The resulting free radicals, the chemical precursors, and the UV

radiation are thought to be the products that rapidly destroy vegetative microorganisms

including spores.

Sterrad

The Sterrad 100 sterilizer was the first plasma sterilizer for use in health care facilities and

has been on the market in Europe since 1990 and in the United States since 1993. In August

1997, the Sterrad 100 System was approved to sterilize certain surgical instruments with

long lumens, such as those used in urologic, laparoscopic, and arthroscopic procedures,

including instruments with single stainless steel lumens of ≥3 and <400 mm in length. The

Sterrad 100S has since replaced the Sterrad 100. The Sterrad 100S adds one sterilization

cycle and thereby fulfills the requirement to kill 106 spores halfway through the cycle. A

smaller device, the Sterrad 50, has been independently tested for efficacy (222). Other sizes,

e.g., the large Sterrad 200, approved by the FDA in 2003, can sterilize small lumens (single

stainless steel lumens with an inside diameter of 1 mm or larger or Teflon/polyethylene

lumens with an inside diameter of 6 mm or larger). The new Sterrad NX System, approved

by the FDA in April 2005, is the fastest low-temperature hydrogen peroxide gas plasma

sterilizer yet. This system employs a new vaporization system that removes most of the

water from the hydrogen peroxide, improving diffusion of peroxide into lumens.

Consequently, a broad range of instruments, including single-channel flexible endoscopes,

can be processed within 38 min. In 2001, the FDA cleared biological indicators suitable for

plasma sterilization.

Regardless of the model, the basic steps are the same. Medical instruments are placed in the

sterilization chamber, a strong vacuum is created in the chamber, and a solution of 59%

hydrogen peroxide and water is automatically injected from a cassette into the sterilization

chamber. The solution vaporizes and diffuses throughout the chamber, surrounding the items

to be sterilized. Radiofrequency energy is applied to create an electric field, which in turn

generates the low-temperature plasma, inducing free radicals. The combination of the

diffusion pretreatment and plasma phases sterilizes the item while eliminating harmful

residuals. At the end of the cycle, the radiofrequency energy is turned off, the vacuum is

released, and the chamber is filled with filtered air, returning it to normal atmospheric

pressure.

Plasma sterilizers have several disadvantages. First, materials that absorb too much

hydrogen peroxide (e.g., cellulosics and some nylons such as those from connectors, cables,

and insulators), materials that catalytically decompose hydrogen peroxide (e.g., copper and

nickel alloys from electrical wire, solder, and surgical instruments), and materials that react

with hydrogen peroxide such as organic dyes (colored anodized aluminum) and organic

sulfides of solid lubricant in endoscopic devices) cannot be sterilized in a Sterrad. Second,

the cassettes required to run the device and the special nonmuslim wrapper are relatively

expensive.

Low-Temperature Sterilization by Ozone

The 125L Ozone Sterilizer (TSO3, Quebec Canada) uses medical-grade oxygen, water, and

electricity to generate ozone within the sterilizer to provide an efficient sterilant without

producing toxic chemicals or using high temperatures. (It runs at 25 to 35°C). Ozone forms

when oxygen is submitted to an intense electrical field that separates oxygen molecules into

atomic oxygen (O), which in turn combines with other oxygen molecules (O2) to form

triatomic oxygen (O3) or ozone, providing a sterility assurance level of 10-6 in approximately

4 h. At the end of the cycle, the oxygen and water vapor safely vent directly into the room.

The sterilization chamber has a capacity of 125 liters. Processed medical instruments require

no aeration at the end of the sterilization cycle. Medical devices are packaged in a TSO3

sterilization pouch or inanodized aluminum sterilization containers. The TSO3 OZO-TEST selfcontained

biological and chemical indicators should be used to evaluate the machine’s

performance. An ozone sterilizer can be installed as a free-standing unit or recessed behind a

wall. These devices are used primarily in Canada. These sterilizers are approved by the FDA,

but few health care facilities in the United States use them.

Liquid Sterilization

The FDA approved the Steris System 1 in 1988, but it is not considered a sterilizer in Europe

(77). The machine is designed to sterilize immersible devices, including flexible endoscopes,

with 35% liquid peracetic acid (an FDA- approved sterilant that is sporicidal [132, 135]),

supplemented with buffering, anticorrosion, wetting, and surface-active agents. Peracetic

acid is automatically diluted with sterile filtered water, and the items are exposed for 12 min.

The entire sterilization process takes approximately 30 min at ca. 50°C. Items can be used

immediately after the process is completed and do not need to be aerated.

Clinical studies of the Steris System 1 have been performed with bronchoscopes,

hysteroscopes, colonoscopes, and rigid endoscopes (42, 272). Independent efficacy tests

demonstrated some failures (42). Exposure time and temperature are monitored

electronically, and conductivity is used as a surrogate marker for peracetic acid

concentration. However, the machine can complete its cycle normally and print a report

stating that the concentration of peracetic acid was in the normal range when it was run

intentionally without peracetic acid (171). Commercially available spores can be used for

monitoring sterilization (155), but false- positive test strips can occur as a result of improper

use of the clip used to attach the test strips (119). Other disadvantages of this system

include the high cost of purchasing and using the equipment, which is considerably greater

than the cost of purchasing and using systems for high-level disinfection with glutaraldehyde

(104). In addition, the device does not clean the items. Thus, the cleaning step adds to the

overall time of reprocessing the items. The Steris System 1, like all other nonsteam

sterilizers, cannot meet the requirements for sterilization if residual debris and/or proteins

are present on the items. The system has been considerably improved over the last decade,

but the changes have not yet been approved by the FDA, which has issued a letter of

concern