This 2005 colorized scanning electron micrograph
(SEM) depicted numerous clumps of methicillin-resistant Staphylococcus
aureus bacteria, commonly referred to by the acronym, MRSA;
Magnified 4780.Courtesy of CDC/
Janice Carr; Jeff Hageman. Photo courtesy of Janice Carr.
The CDC released, in 2008,
Guidelines for Disinfection and Sterilization in Healthcare
Facilities, 2008 (Rutala, et al., 2008).
The following information is largely taken from that document.
the presence of microorganisms on an item or surface.
Cleaning is the removal
of visible soil and foreign materials (e.g., organic and inorganic
material such as dirt, body fluids, lubricants) from objects
and surfaces and normally is accomplished manually or mechanically
using water with soaps, detergents or enzymatic products,
through washing or scrubbing the object or surface. Thorough
cleaning is essential before high-level disinfection and sterilization
because inorganic and organic materials that remain on the
surfaces of instruments interfere with the effectiveness of
the use of physical or chemical means to remove, inactive
or destroy pathogens on a surface or item to the point where
they are no longer capable of transmitting infectious particles.
Decontamination removes pathogenic microorganisms from items
so they are safe to handle, use, or discard.
the removal or destruction of all microorganisms and their
spores. Sterilization describes a process that destroys
or eliminates all forms of microbial life and is carried out
in health-care facilities by physical or chemical methods.
Steam under pressure, dry heat, EtO gas, hydrogen peroxide
gas plasma, and liquid chemicals are the principal sterilizing
agents used in health-care facilities. Sterilization is intended
to convey an absolute meaning; unfortunately, however,
some health professionals and the technical and commercial
literature refer to "disinfection" as "sterilization" and
items as "partially sterile." When chemicals are used to destroy
all forms of microbiologic life, they can be called chemical
sterilants. These same germicides used for shorter exposure
periods also can be part of the disinfection process (i.e.,
a process that eliminates many or all pathogenic microorganisms,
except bacterial spores, on inanimate objects. In healthcare
settings, objects usually are disinfected by liquid chemicals
or wet pasteurization. Each of the various factors that affect
the efficacy of disinfection can nullify or limit the efficacy
of the process. Factors that affect the efficacy of both disinfection
and sterilization include prior cleaning of the object; organic
and inorganic load present; type and level of microbial contamination;
concentration of and exposure time to the germicide; physical
nature of the object (e.g., crevices, hinges, and lumens);
presence of biofilms; temperature and pH of the disinfection
process; and in some cases, relative humidity of the sterilization
process (e.g., ethylene oxide).
- High-level disinfection is capable of killing all
organisms, except high levels of bacterial spores, and is
effected with a chemical germicide cleaned for marketing
as a sterilant by the FDA.
- Intermediate level agent destroys all vegetative
bacteria, including tubercle bacilli, lipid and some nonlipid
viruses, and fungi, but not bacterial spores. These agents
are registeres as "tuberculocide" by the US Environmental
Protection Agency (EPA).
- Low-level agent is one that destroys all vegetative
bacteria (except tubercle bacilli), lipid viruses, some
nonlipid viruses, and some fungi, but not bacterial spores.
These agents are registered as a hospital disinfectant by
The CDC Guidelines utilize the Spauling classification, which
divides instruments and items for patient care into critical,
semicritical or non-critical items. Depending on the category,
planning for disinfection or sterilization can be determined
for the most part.
- Critical items are those that enter sterile tissue
or the vascular system and must be sterile. Critical items
have a high risk for infection if they are contaminated
with any microorganism. This category includes surgical
instruments, cardiac and urinary catheters, implants, and
ultrasound probes used in sterile body cavities.
Most of the items in this category should be purchased
as sterile or be sterilized with steam if possible. Heat-sensitive
objects can be treated with EtO, hydrogen peroxide gas
plasma; or if other methods are unsuitable, by liquid
chemical sterilants. Germicides categorized as chemical
sterilants include >/=2.4% glutaraldehyde-based formulations,
0.95% glutaraldehyde with 1.64% phenol/phenate, 7.5% stabilized
hydrogen peroxide, 7.35% hydrogen peroxide with 0.23%
peracetic acid, 0.2% peracetic acid, and 0.08% peracetic
acid with 1.0% hydrogen peroxide. Liquid chemical sterilants
reliably produce sterility only if cleaning precedes treatment
and if proper guidelines are followed regarding concentration,
contact time, temperature, and pH.
- Semicritical items contact mucous membranes or
nonintact skin. This category includes respiratory therapy
and anesthesia equipment, some endoscopes, laryngoscope
blades, esophageal manometry probes, cystoscopes, anorectal
manometry catheters, and diaphragm fitting rings. These
medical devices should be free from all microorganisms;
however, small numbers of bacterial spores are permissible.
Intact mucous membranes, such as those of the lungs and
the gastrointestinal tract, generally are resistant to infection
by common bacterial spores but susceptible to other organisms,
such as bacteria, mycobacteria, and viruses.
Semicritical items minimally require high-level disinfection
using chemical disinfectants. Glutaraldehyde, hydrogen
peroxide, ortho-phthalaldehyde, and peracetic acid with
hydrogen peroxide are cleared by the Food and Drug Administration
(FDA) and are dependable high-level disinfectants provided
the factors influencing germicidal procedures are met.
When a disinfectant is selected for use with certain patient-care
items, the chemical compatibility after extended use with
the items to be disinfected also must be considered. Semicritical
items minimally require high-level disinfection using
- Non-critical items are those that come in contact
with intact skin but not mucous membranes. Intact skin acts
as an effective barrier to most microorganisms; therefore,
the sterility of items coming in contact with intact skin
is "not critical." In the CDC Guideline, noncritical items
are divided into noncritical patient care items and noncritical
environmental surfaces. Examples of noncritical patient-care
items are bedpans, blood pressure cuffs, crutches and
computers. In contrast to critical and some semicritical
items, most noncritical reusable items may be decontaminated
where they are used and do not need to be transported to
a central processing area. Virtually no risk has been documented
for transmission of infectious agents to patients through
noncritical items when they are used as noncritical items
and do not contact non-intact skin and/or mucous membranes.
Most Environmental Protection Agency (EPA)-registered disinfectants
have a 10-minute label claim. Federal law requires all applicable
label instructions on EPA-registered products to be followed:
use-dilution, shelf life, storage, material compatibility,
safe use, and disposal. Noncritcal environmental surfaces
include bed rails, some food utensils, bedside tables, patient
furniture and floors.
Noncritical environmental surfaces frequently
touched by hand (e.g., bedside tables, bed rails) potentially
could contribute to secondary transmission by contaminating
hands of healthcare workers or by contacting medical equipment
that subsequently contacts patients. Mops and reusable
cleaning cloths are regularly used to achieve low-level
disinfection on environmental surfaces. However, they
often are not adequately cleaned and disinfected, and
if the water-disinfectant mixture is not changed regularly
(e.g., after every three to four rooms, at no longer than
60-minute intervals), the mopping procedure actually can
spread heavy microbial contamination throughout the healthcare
facility. In one study, standard laundering provided acceptable
decontamination of heavily contaminated mopheads but chemical
disinfection with a phenolic was less effective. Frequent
laundering of mops (e.g., daily), therefore, is recommended.
Single-use disposable towels impregnated with a disinfectant
also can be used for low-level disinfection when spot-cleaning
of noncritical surfaces is needed.
The CDC, in the Guidelines, identifies the limitation of
the Spaulding classification system with complicated medical
equipment, particularly with complicated medical equipment
and those that are in the semi-critical category. Choosing
the best method for disinfection/sterilization can be difficult.
According to the Guidelines (2008, p. 13):
This is true particularly for a few medical devices (e.g.,
arthroscopes, laparoscopes) in the critical category because
of controversy about whether they should be sterilized or
high-level disinfected. Heat-stable scopes (e.g., many rigid
scopes) should be steam sterilized. Some of these items
cannot be steam sterilized because they are heat-sensitive;
additionally, sterilization using ethylene oxide (EtO) can
be too time-consuming for routine use between patients (new
technologies, such as hydrogen peroxide gas plasma and peracetic
acid reprocessor, provide faster cycle times). However,
evidence that sterilization of these items improves patient
care by reducing the infection risk is lacking. Many newer
models of these instruments can withstand steam sterilization,
which for critical items is the preferred method.
Another problem with implementing the Spaulding scheme
is processing of an instrument in the semicritical category
(e.g., endoscope) that would be used in conjunction with
a critical instrument that contacts sterile body tissues.
For example, is an endoscope used for upper gastrointestinal
tract investigation still a semicritical item when used
with sterile biopsy forceps or in a patient who is bleeding
heavily from esophageal varices? Provided that high-level
disinfection is achieved, and all microorganisms except
bacterial spores have been removed from the endoscope, the
device should not represent an infection risk and should
remain in the semicritical category . Infection with spore-forming
bacteria has not been reported from appropriately high-level
An additional problem with implementation of the Spaulding
system is that the optimal contact time for high-level disinfection
has not been defined or varies among professional organizations,
resulting in different strategies for disinfecting different
types of semicritical items (e.g., endoscopes, applanation
tonometers, endocavitary transducers, cryosurgical instruments,
and diaphragm fitting rings). Until simpler and effective
alternatives are identified for device disinfection in clinical
settings, following this guideline, other CDC guidelines
and FDA-cleared instructions for the liquid chemical sterilants/high-level
disinfectants would be prudent.