++
Although the terms are often used interchangeably, disinfectants
and antiseptics have specific definitions (Table 30–1).
Disinfectants are chemical agents that inhibit or kill various microorganisms
on nonliving objects in the environment (Table 30–2). They
should not be used on living tissue. Antiseptics inhibit microorganism
growth and reproduction on inanimate objects, but they are also
safe enough to be used on the surfaces of living tissue, such as
skin. Notably, disinfectants and antiseptics do not have selective
toxicity; each agent displays a different microbicidal profile that
must be considered for appropriate and effective use. Sterilization refers to the use of physical or
chemical means to destroy all microbial life, including highly resistant
bacterial endospores.
++
Disinfection involves the destruction of infective organisms
by physical or chemical means (Table 30–2), reducing the
number of potentially infective organisms either by killing, removing, or
diluting them. Disinfection is often accomplished by ionizing radiation
or dry or moist heat.
++
The ideal disinfectant would be able to kill all pathogenic microorganisms
without harming healthy human tissue. Since the ideal disinfectant
does not exist, a combination of agents is often used (e.g., addition
of a disinfectant to a detergent), and the choice of which to use
depends on the particular situation.
++
Washing, which dilutes and partially removes potentially infectious
organisms, and the use of barriers (e.g., gloves, condom, respirator),
which prevent pathogens from gaining entry into the host, are foremost
in infection prevention and control.
++
Hand washing is the single most important way to prevent transmission
of pathogens from person to person or from regions of higher microbial
load (e.g., mouth, nose, gut) to potential sites of infection. Although
hand washing with soap and water effectively removes and dilutes
most infectious agents, skin disinfectants are added to detergents
for preoperative surgical cleansing of the surgeon’s hands
and the patient’s surgical incision site. To minimize irritation,
dryness, and skin sensitization, regular hand washing should be
done without disinfectants. In addition, for regular hand washing,
it may be preferable to create conditions that are inhospitable
to bacterial reproduction rather than to kill bacteria with disinfectants.
Because of their rapid reproduction rate, it is possible that survival
of bacteria following an antiseptic challenge may result in increased
propagation of strains of antiseptic-resistant bacteria. For this
reason, the wisdom of the current trend of adding antibacterial
agents to regular hand soap and impregnated cloths and fabrics may
be questioned.
+++
Appropriate
Choice of a Disinfectant, Antiseptic, or Sterilant
++
The choice of antiseptic, disinfectant, or sterilant (or combination)
depends on several factors including, but not limited to, risk of
infection associated with the use of each agent, intrinsic resistance
of the microorganism, number of microorganisms present (microbial
load), mixed populations of organisms, amount of organic material
present (e.g., blood, feces, tissue), stability and concentration
of agent, time and temperature of exposure, pH, and hydration and
binding of the agent to surfaces.
++
As noted, disinfectants, antiseptics, and sterilants do not have
selective toxicity. Every agent has more or less marked cytotoxic
properties. For cleansing wounds, antiseptics are often avoided because
they interfere with wound healing. Thus, both the patient and health-care
professionals must consider the short-term and long-term toxicity
of each agent. The Environmental Protection Agency (EPA) regulates
disinfectants and sterilants and the Food and Drug Administration (FDA)
regulates antiseptics. Major classes of antiseptics, disinfectants,
and sterilants are described below.
++
The most frequently used alcohols for treatment table disinfection
and skin antisepsis are ethanol and isopropyl alcohol (isopropanol). Alcohols
rapidly kill vegetative bacteria, Mycobacterium
tuberculosis, and many fungi. Alcohol’s biocidal effects
are due to its ability to dehydrate cells, disrupt membranes, and
coagulate proteins. Exposure to 70 to 80% ethanol or isopropanol
(by volume in water) for at least 5 minutes is the best practice
for optimal surface and skin disinfection. These high-concentration
alcohol mixtures also quickly and effectively inactivate HIV and
hepatitis B and C viruses on surfaces. Alcohols are not considered
sterilants because they do not inactivate spores, penetrate protein-containing
organic material, or inactivate hydrophilic viruses. In addition,
rapid evaporation prevents alcohols from having a lasting residual
action. Alcohols are useful in situations in which access to running
water and soap is limited (e.g., home
care setting). To limit their skin-drying effect, emollients are
often added to hand-use antiseptic formulations. Because of alcohols’ flammability,
they should be used and stored in cool and well-ventilated areas.
Their complete evaporation must be allowed before use of any flame, cautery,
or lasers.
++
Formaldehyde and glutaraldehyde (sometimes called cold
sterilants) are used for high-level disinfection or sterilization
of medical instruments that cannot tolerate exposure to the high
temperatures required for steam sterilization (autoclaving). Thus,
they are used for sterilizing plastic and rubber and equipment that
cannot be autoclaved. By cross-linking proteins and nucleic acids,
aldehydes inactivate a broad spectrum of microorganisms and viruses.
Aldehyde disinfection or sterilization may fail if dilutions are
below effective concentrations, if organic material is present,
or if the liquid formulation is unable to penetrate into crevices
in medical instruments. For this last reason, circulating baths
can be used to increase penetration of aldehyde solutions, while
decreasing exposure of the operator to irritating fumes.
++
Formaldehyde is available as a 40% weight/volume
solution in water (100% formalin). At a concentration of
8%, formaldehyde exhibits a broad spectrum of activity
against bacteria, bacterial toxins, spores, viruses, and fungi.
Destruction of spores may take up to 18 hours, but the speed of action
may be increased by solution in 70% alcohol. Alcohol probably
strips protective lipids, allowing formaldehyde better access to
the pathogen. Formalin is used for high-level disinfection of hemodialyzers,
preparation of vaccines, and embalming of tissues.
++
A 2% glutaraldehyde solution is activated by alkali
for use as a broad-spectrum disinfectant. Specific applications
for its use include disinfecting respiratory therapy equipment,
physical therapy whirlpool tubs, and dialysis treatment equipment.
Glutaraldehyde is found in commonly used products such as Cidex,
Hospex, and Sonacide. While glutaraldehyde has greater sporicidal
activity than formaldehyde, it may not be as effective at killing M tuberculosis. Once activated by
alkali, glutaraldehyde begins to polymerize. Thus, its activated
shelf life is about 2 weeks. Test strips are available to measure
activity.
++
Formaldehyde and glutaraldehyde are highly irritating to the
skin, eye, and respiratory tract even at low levels for short periods.
Formaldehyde gas has a distinctive, pungent, and irritating odor that
is detectable even at extremely low concentrations (<1 ppm).
The Occupational Safety and Health Administration (OSHA) has declared
that formaldehyde is a potential carcinogen and has established
an exposure standard that limits the 8-hour time-weighted exposure
of employees to 0.75 ppm (permissible exposure limit [PEL]).
However, for sensitized individuals, odor may not be an adequate
indicator of the presence of formaldehyde and may not provide a
reliable warning of hazardous concentrations. Because it is slightly
heavier than air, vapors can result in asphyxiation in poorly ventilated,
enclosed, or low-lying areas. Glutaraldehyde solutions are pale
yellow liquids with a rotten-apple odor. Although OSHA does not
currently have a required PEL for glutaraldehyde, the National Institute
for Occupational Safety and Health (NIOSH) has established a recommended
exposure limit of 0.2 ppm. There are several ways to minimize or
limit occupational exposure to the aldehydes, including ensuring
the agents are used in fume hoods with exhaust ventilation, using
only enough to perform required disinfecting procedure, avoiding
skin contact by use of personal protective equipment (PPE) such
as gloves, goggles, face shields, and respirators. Gloves should
be made of nitrile or butyl rubber because latex gloves do not provide adequate
protection.
++
For many years, heavy metal salts were used as antiseptics and
disinfectants because of their ability to denature proteins. Most
heavy metal ion preparations are now considered to be too toxic
for routine use. However, mercury and silver still have a limited number
of applications.
++
Mercury is an environmental hazard, and many strains of bacteria
have developed resistance to mercurials. While the use of mercury-containing
preservatives has declined in recent years because of an increasing
awareness of the theoretic potential for neurotoxicity, thimerosal is still used as a preservative
(0.001 to 0.004%) in numerous biologic and drug products,
including immune sera, antitoxins, and certain vaccines. Notably,
thimerosal was removed from or reduced to trace amounts in all vaccines
routinely recommended for children ≤6 years
of age except for influenza vaccines. Mercurochrome, generically
known as merbromin, was a popular topical antiseptic for years.
In 1998, the FDA declared merbromin “not generally recognized
as safe and effective” because of concerns about its mercury
content. Although distribution has effectively been discontinued
in the United States, it is still available in most other countries.
++
Inorganic silver salts are strongly bactericidal. Bacterial (and
probably fungal) silver sensitivity relates to silver’s
ability to irreversibly denature key enzyme systems. Silver exhibits
low toxicity in humans, with minimal expected risk from clinical
exposure by dermal applications or through urologic and hematogenous
routes. Silver sulfadiazine (1%)
is a widely used safe and effective topical cream used to help prevent
gram-positive and gram-negative bacterial colonization of burned
skin and tissues. Physical therapists should be aware that a blue-black
pseudoeschar forms over the wound surface that must be removed before more
cream is applied or wound healing will be hindered.
++
Over the past 5 years, silver has undergone a renaissance as
a topical antibacterial agent in wound healing. It is incorporated
into virtually all classes of wound dressings. The popularity of
silver-based antimicrobial dressings may be due to new formulations
allowing slow and sustained release of silver, newer research indicating
that colonized wounds display delayed wound healing, and aggressive
manufacturer marketing. The majority of in vivo studies indicate
that silver dressings decrease wound bioburden and may be effective
against antibiotic-resistant organisms (e.g., Staphylococcus, Pseudomonas, Enterococcus);
however, bacterial resistance may occur. Although some evidence
suggests that silver retards wound epithelialization, the majority
of in vivo evidence suggests that silver is not cytotoxic to viable
cells.
+++
Halogens (Iodine,
Iodophors, Chlorine)
++
Iodine antiseptics have a wide spectrum of antimicrobial and
antiviral activity. Thus far, microorganisms appear unable to develop
resistant strains to iodine. Iodine in a 1:20,000 solution is bactericidal
within one minute and sporicidal within 15 minutes. It is usually
used in an alcohol solution called tincture of iodine as a preoperative
antiseptic for intact skin. Although iodine preparations are effective
bactericidals, many studies have demonstrated some degree of cytotoxicity, impaired
wound healing, and reduced wound strength. In addition, iodine use
is decreasing because of serious hypersensitivity reactions and
its propensity to stain clothing and dressings.
++
Iodophors are mixtures of iodine with solubilizing agents such
as surfactants or povidone. Iodophor topical solutions release free
iodine, but are more gentle to the skin, less likely to provoke
hypersensitivity reactions, and less likely to stain fabric than
tincture of iodine. Although they maintain germicidal action, the
effectiveness of any iodophor depends on the percentage of released
free iodine. They may be used as antiseptics or disinfectants, with
the latter containing more free iodine. The most common iodophor
is povidone-iodine
(polyvinylpyrolidone [PVP]); marketed as
Betadine. Povidone itself has no germicidal action; it controls
the release of the inorganic iodine. Povidone-iodine is widely used
for cleaning dirty wounds, scrubbing surgeons’ hands, and
patients’ intact preoperative surgical site. Povidone iodine
has not been proven to be effective for decontaminating medical
equipment.
++
When chlorine dissolves in water, hypochlorous acid is produced.
Chlorine is a fairly universal and inexpensive disinfectant. It
is found most commonly as a 5.25% sodium hypochlorite
solution in the form of common household bleach. Depending on the
concentration, sodium hypochlorite is
effective against most common pathogens, including HIV, tuberculosis,
hepatitis B and C, fungi, antibiotic-resistant strains of staphylococci,
and enterococci. The Centers for Disease Control and Prevention
(CDC) recommends a 1:10 dilution of 5.25% household bleach
(5000 ppm of available chlorine) for disinfecting blood spills.
At this concentration, most pathogens and spores are killed or inactivated.
The exception is that a concentration range of 1,000 to 10,000 ppm
is required to kill mycobacteria. In a recent review of 33 studies,
sodium hypochlorite was effective for sterilization at a concentration
of 5000 ppm for 5 minutes and for disinfection at 1000 ppm for 10
minutes. Dilutions of sodium hypochlorite in water (pH 7.5 to 8.0)
will retain antimicrobial activity for months if kept in tightly
closed opaque containers. However, frequent opening and closing
markedly reduces its efficacy.
++
Because chlorine is inactivated by blood, serum, feces, and protein-containing
materials, organic material must be removed from the surface to
be disinfected prior to use of sodium hypochlorite. Thus, bleach
is an excellent disinfectant, but a poor cleaner. After cleaning,
a 1:10 solution is effective simply by being wiped on and left to
dry. Extreme caution must be taken not to combine sodium hypochlorite
with either ammonia or with any acid because irritating chlorine
gas evolves. If sodium hypochlorite solution contacts a product
containing formaldehyde, a carcinogenic compound results. The best
practice is not to add anything to sodium hypochlorite except water. Sodium
hypochlorite solutions are caustic to the skin and eyes, so users
should wear rubber gloves and—if ventilation is not ideal—goggles.
Sodium hypochlorite solutions are corrosive to aluminum, silver,
and stainless steel.
++
Chlorhexidine gluconate is a water-soluble antiseptic whose bacteriostatic
and bactericidal properties arise from its ability to disrupt bacterial
membranes. It is more effective against gram-positive cocci and
mycobacteria and less effective against gram-negative rods. It also
has moderate activity against fungi and viruses. Chlorhexidine inhibits
spore germination (unlike alcohol-based antiseptics), and is effective
in the presence of blood and organic materials (unlike sodium hypochlorite).
++
One of the primary uses of chlorhexidine is as an oral mouthwash
used in the prevention and treatment of gingivitis. This application
may be appropriate in patients who cannot independently or adequately
brush their teeth because it provides up to 24 hours of antimicrobial
activity. Nondental uses for chlorhexidine include preoperative
skin preparation and antiseptic hand wash (Hibiclens: 4% chlorhexidine
gluconate) against MRSA. Chlorhexidine is inactivated by anionic and
nonionic compounds found in many mouthwashes, toothpastes, soaps,
and moisturizers. Chlorhexidine mouth rinses should be used approximately
2 hours after use of other dental products. Likewise, hand moisturizers
or soaps should not be used after hand washing with chlorhexidine
immediately prior to patient care. Because chlorhexidine binds strongly
to the skin and mucosa, it has significant residual activity; it
inhibits the proliferation or survival of microorganisms after application.
Often, low concentrations (0.5% to 1.0%) of chlorhexidine
are added to alcohol-based hand-washing preparations to increase
the residual activity of alcohol alone. Chlorhexidine is safe for
cleansing the skin of adults and infants, and has a low potential
for eliciting skin sensitivity. Although uncommon, skin irritation
is concentration dependent, so products containing 4% chlorhexidine
are the most likely to cause skin reactions with frequent use. Eye
contact should be avoided because it can cause corneal damage.
++
Phenol was the first disinfectant to be used in clinical medical
practice. Although effective, it is highly corrosive, toxic upon
absorption, and carcinogenic. Many less toxic derivatives of phenol have
been developed. Among the most popular are hexachlorophene and
chlorhexidine (discussed above).
++
Phenolic disinfectants are commonly used for hard surface decontamination
in hospitals (e.g., floors, counters, beds). Phenolics are bactericidal
(including mycobacteria), fungicidal, and capable of inactivating
many viruses such as HIV and herpes simplex types 1 and 2. Phenolics
do not destroy spores.
++
Because of its bacteriostatic properties (especially against S aureus), hexachlorophene was
widely used as an antiseptic hand wash in hospitals. It has residual
activity for several hours after use and gradually reduces bacterial
counts on hands after repetitive use. However, with repeated use,
hexachlorophene is absorbed through the skin. In 1972, the FDA warned
that hexachlorophene should not be used routinely to bathe infants
because of its potential neurotoxic effects. Hexachlorophene should
not be used to bathe patients with burns or extensive areas of sensitive
skin. Soaps containing 3% hexachlorophene are available
by prescription only, and routine use of hexachlorophene is generally
not recommended for hand antisepsis.
++
When used at appropriate concentrations, the peroxygen compounds, hydrogen peroxide and peracetic acid, are useful as disinfectants
and sterilants. Their advantages include effectiveness against a
wide variety of organisms (bacteria, yeast, fungi, viruses, and
spores) and the fact that their decomposition products (oxygen
and water) are nontoxic. The primary disadvantage is a rather short-lived antimicrobial
effect.
++
Hydrogen peroxide’s killing ability is due to the hydroxyl
radical, which is one of the strongest oxidants known. It is an
effective disinfectant when used for inanimate objects with low
water content. Anaerobes are most sensitive because they do not
produce catalase, which breaks down peroxide. In the home, hydrogen
peroxide can be found in diluted form (3% to 10%),
whereas industrial uses involve concentrated solutions (30% or
greater). Hydrogen peroxide is not stable; it must be protected
from light and kept in a cool place because light and heat exposure
cause degradation. Hydrogen peroxide is used to disinfect surfaces
such as respirators, plastic eating utensils, and soft contact lenses.
To be an effective sporicidal, concentrations of 10 to 25% are required.
Dilute hydrogen peroxide is used as a mouthwash to help control
plaque, although it has not been proven to be effective in critically
ill patients. Finally, hydrogen peroxide was previously used in
first aid kits to disinfect and debride wounds. When applied to
a wound, hydrogen peroxide combines with catalase produced in tissues,
decomposing into oxygen and water and producing effervescence. It
was rationalized that this process helped loosen necrotic or inorganic material
that might inhibit wound healing. However, hydrogen peroxide damages
healthy cells (keratinocytes and fibroblasts) required for wound
healing. Thus, hydrogen peroxide is no longer recommended for wound
care.
++
Peracetic acid is a mixture of hydrogen peroxide and acetic acid
in a watery solution. Since it is explosive in pure form, it is
used in dilute solution and transported in vented containers to
prevent increased pressure as oxygen is released. As with hydrogen
peroxide, the hydroxyl radical released from peracetic acid is the
lethal species. Peracetic acid is a stronger bactericidal and sporicidal
agent than hydrogen peroxide. At room temperature, 250 to 500 ppm
peractic acid is effective against most bacteria when applied to
contaminated surfaces for 5 minutes. Destruction of spores is increased
with both a rise in temperature and an increase in concentration
(500 to 300,000 ppm). Effectiveness is slightly decreased by the
presence of organic matter, but can be maintained by an increase
in concentration. Peracetic acid may be formulated as a liquid spray
or mop-on solution. Automatic sterilization systems using low concentrations
of peracetic acid (0.1% to 0.5%) have been designed
to sterilize medical and dental instruments.
+++
Quaternary Ammonium
Compounds
++
Quaternary ammonium compounds (“quats”) are
cationic surface-active detergents widely used in hospitals for
disinfection of noncritical hard surfaces such as bench tops and
floors. They are most likely to be encountered by health-care workers
in central supply, housekeeping, and patient and surgical services
areas. Benzalkonium chloride is the
most widely used quat antiseptic. Other quats used as antiseptics
are cetrimide, cetylpyridium chloride,
and benzethonium chloride.
++
Quaternary ammonium compounds are mostly bacteriostatic, sporistatic,
and fungistatic, although they are microbicidal against certain
pathogens at higher concentrations. Antimicrobial activity probably
involves cell membrane disruption. They are ineffective against
mycobacteria and gram-negative bacteria. In addition, their antimicrobial
activity is antagonized by the presence of organic material, soaps,
many nonionic detergents, and calcium, magnesium, ferric, and aluminum
ions. Several strains of S aureus have
recently been described with genetic resistance to quaternary ammonium
compounds. Because contamination of stock solutions with gram-negative
rods can be a problem, the CDC has recommended that benzalkonium
chloride and other similar quaternary ammonium compounds not be
used as antiseptics.
++
When all microbial life, including highly resistant bacterial
endospores, must be destroyed, sterilization is required. Sterility
is an absolute term meaning there are no relative degrees of sterility. Sterilization
can be performed by physical or chemical means. During chemical
sterilization, sterilants are applied to materials for appropriate
times and temperatures.
++
The recommended sterilization for biohazardous material is autoclaving—the
use of pressurized steam at a temperature of 120°C
for a minimum of 30 minutes. Autoclaving medical and surgical instruments
can only be done when these materials do not contain plastic or
rubber. In the latter case, gas sterilization may be performed.
Although few gases are able to kill microbes, ethylene oxide gas
is a highly effective disinfectant, and kills spores rapidly. Widespread
use of ethylene oxide is limited by its extreme flammability, its
cost, and its classification as a mutagen and carcinogen. OSHA’s
permissible exposure level for ethylene oxide is 1 ppm as a time-weighted
measure. Alternative sterilants are increasingly being employed,
such as vapor phase hydrogen peroxide, peracetic acid, ozone, gas plasma,
chlorine dioxide, formaldehyde, and propylene oxide.
++
Preservatives are required to prevent microbial growth and contamination
in many pharmaceutical, cosmetic, and therapy-related products in
multiple-use containers such as ultrasound gel or friction massage
cream. The ideal preservative must be effective against a broad
spectrum of microorganisms, soluble, stable, and nonirritating to
tissues to which they are applied.
++
Commonly used preservatives include benzoic
acid and salts, parabens, sorbic acid and
salts, propylene glycol, phenolic compounds, quaternary ammonium
salts, alcohols, and mercurials such as thimerosal. To inhibit S aureus and Escherichia
coli, the concentration of propylene glycol must exceed 10%.
At this concentration, propylene glycol is a skin sensitizer. Although
rare, cases of contact dermatitis from preservatives in ultrasonic
gels have been reported. Health-care professionals should investigate
the type and concentration of preservative in any product prior
to patient application.