Sterilization and Disinfection

Question 1

Sterilization

Answer 1

Sterilization is the complete elimination or destruction of all forms of microbial life.
This is accomplished by either physical or chemical processes.

Question 2

Disinfection

Answer 2

Disinfection describes a process that eliminates many or all-pathogenic micro-organisms on inanimate objects with the exception of bacterial spores.
It is usually accomplished by the use of liquid chemicals.

Question 3

Cleaning

Answer 3

Cleaning is the removal of visible soil (e.g. organic and inorganic material) from objects and surfaces.
Usually this is accomplished by manual or mechanical means using water with detergents or enzymatic products.

Question 4

Spaulding categories for sterilization: critical

Answer 4

Critical objects are those which enter normally sterile tissue or the vascular system or through which blood flows. They have a high risk of infection and should be sterilized. Examples include surgical instruments, urinary catheters and needles.

Question 5

Spaulding categories for sterilization: semi-critical

Answer 5

Semi-critical objects are those which touch mucous membranes or skin that is not intact. As intact mucous membranes are generally resistant to infection, such equipment poses an intermediate risk. Hence they require a disinfection process (high-level disinfection) that kills all micro-organisms except high numbers of bacterial spores.

Question 6

Spaulding categories for sterilization: non-critical

Answer 6

Non-critical objects are those which touch only intact skin. As skin is an effective barrier to micro-organisms, such equipment poses a low risk of infection. Hence, they require low-level disinfection. Examples of non-critical items are bedpans and blood pressure cuffs.

Question 7

Sterility assurance value, or SAL

Answer 7

A sterile device has a SAL of 10⁻⁶, which means that the probability of an organism surviving on that device is one in a million.

Question 8

Methods of sterilization: (moist) steam

Answer 8

Moist steam is the most widely used and dependable method of sterilization. There are four parameters:

• Steam
• Pressure
• Temperature
• Time

Two recognised temperatures and times are:

• 30 minutes at 121°C for wrapped medical items
• 4 minutes at 132°C

Question 9

Methods of sterilization: ethylene oxide gas

Answer 9

Low temperature sterilization can be accomplished with ethyene oxide gas. It is very effective at killing micro-organisms, penetrates plastic and packaging and is compatible with most materials.

However, it is a hazard to humans, expensive and requires a long time (24h)

Question 10

Methods of sterilization: hydrogen peroxide gas plasma sterilization

Answer 10

Safe for the environment and health care worker; it leaves no toxic residuals. Fast cycle time. Used for heat and moisture sensitive items (e.g. endoscopes).

However, paper and liquids cannot be processed. Small chamber. Requires synthetic packaging.

Question 11

Methods of sterilization: Ozone

Answer 11

Uses O3 molecules created by an intense electric field

Question 12

Methods of sterilization: Dry Hot Air

Answer 12

Requires high temperature of 160°C for 2 hours - inefficient and lengthy.

Question 13

Methods of sterilization: Ionizing radiation

Answer 13

Ionizing radiation uses gamma rays from cobalt-60 to produce sterility. It is ideal for pre-packed, heat labile, single use items like needles and face masks and is widely used in the industry.

Question 14

Decontamination

Answer 14

Decontamination is the process when pathogens are removed, inactivated or destroyed. This involves cleaning and then disinfection and/or sterilization.

Question 15

Disinfection: thermal washer disinfection

Answer 15

Sprays a device with water and detergent. The device must be able to withstand powerful water jets and repeated exposure to wet heat of 80°C.

Most organisms are inactivated except for bacterial spores, some heat-resistant viruses and cryptosporidia.

Question 16

Disinfection: Pasteurization (or low temperature steam)

Answer 16

Not sterilization, can destroy all pathogenic organisms apart from bacterial spores. Generally >70°C for 30 minutes. Unsuitable for oily/greasy items or those with sealed cavities.

Question 17

Disinfection: Boiling water disinfection

Answer 17

Boiling a device in water for 5 minutes is a cheap and non-toxic way of inactivating most non-sporing micro-organisms, fungi, viruses and some heat-sensitive spores.

Question 18

Disinfection: Chemical disinfectants

Answer 18

A chemical disinfectant is a compound which destroys micro-organisms by chemical or physiochemical means. It can eliminate gram-positive and negative bacteria.

Chemical disinfectants:

• Are less effective against non-enveloped viruses, protozoal cysts and bacterial endospores
• Can be used alone or in combinations
• Are not interchangeable

Question 19

Disinfection: Alcohols

Answer 19

e.g. ethyl alcohol and isopropyl alcohol. Most effective 60-90% volume/volume with water (less than 50% - ineffective).

Alcohols are rapidly bactericidal rather than bacteriostatic against vegetative forms of bacteria; they are also tuberculocidal, fungicidal and virucidal but do not destroy bacterial spores

Flammable

Question 20

Disinfection: Glutaraldehyde

Answer 20

Glutaraldehyde has gained wide acceptance as a high-level disinfectant and chemical sterilant. Antimicrobial activity is dependent not only on age, but also on use conditions such as dilution and organic stress. The use of glutaraldehyde-based solutions in healthcare facilities is widespread because of their advantages. These include:

Excellent biocidal properties
Activity in the presence of organic matter
Non-corrosive action to endoscopic equipment, thermometers, rubber or plastic equipment.

Question 21

Disinfection: Iodophors (iodine-containing solutions)

Answer 21

Iodophors are bactericidal, mycobactericidal and virucidal but may require prolonged contact times to kill certain fungi and bacterial spores. Iodophors have also been used for the disinfection of blood culture bottles and medical equipment such as hydrotherapy tanks, thermometers and, in the past, endoscopes.