Sterilization and disinfection

Question 1

Costs associated with hospital acquired infections in the UK

Answer 1

• Leading cause of preventable diseases
• > 5000 deaths/year
• > £1bn / year

Question 2

Decontamination

Answer 2

= the process whereby pathogens are removed, inactivated of destroyed

Involves
* Thorough cleaning: essential before high-level disinfection and sterilization because inorganic and organic materials that remain on the surfaces of instruments interfere with the effectiveness of these processes
* Then disinfection and/or sterilization

Question 3

Differences between sterilization vs disinfection vs cleaning

Answer 3

**Sterilization **
* = the complete elimination or destruction of all forms of microbial life
* Physical or chemical processes

Disinfection
* = a process that eliminates many or all pathogenic micro-organisms on inanimate objects with the exception of bacterial spores
* Usually using liquid chemicals

**Cleaning **
* = removal of visible soil (organic or inorganic) from objects and surfaces. Physical removal of the infectious material, or organic matter, on which organisms thrive.
* Usually manual or mechanical means using water with detergents or enzymatic products

Question 4

Spaulding categories of instruments/items for patient care

Answer 4

3 categories based on risk of infection involved. Used to plan methods for disinfection or sterilization

Critical: e.g. surgical instruments, urinary catheters, needles
* Enter normally sterile tissue or the vascular system or through which blood flows
* High risk of infection
* Should be sterilized

Semi-critical: e.g. laryngoscope blades
* Touch mucous membranes or skin that is not intact. I
* Intermediate risk of infection (intact mucous membranes are generally resistant to infection)
* Require high-level disinfection: kills all micro-organisms except high numbers of bacterial spores

Non-critical: e.g. bedpans, BP cuffs
* Touch only intact skin - low risk of infection.
* Require low-level disinfection

Question 5

Sterility assurance value (SAL): definition, what is the SAL of a sterile device?

Answer 5

Represents the probability that a device remains contaminated after it has gone through a sterilization process.

A sterile device has a SAL of 10^-6 i.e. probability of organism surviving on that device is 1 in a million

Question 6

What influences efficacy of disinfection and sterilization?

Answer 6

• Cleaning of the object
• Organic and inorganic load present
• Type and level of microbial contamination
• Concentration of, and exposure time to, sterilant
• Nature of the object
• Temperature and relative humidity

Question 7

Sterilization methods: types, uses

Answer 7

• High temperature: Steam (most common), dry hot air (not used in hospitals - higher temp than most medical devices can withstand, relatively inefficient and lengthy)
• Low temperature: ethylene oxide, hydrogen peroxide gas plasma, peracetic acid immersion, ozone, ionizing radiation

Most medical and surgical devices are made of heat stable materials -> sterilised by heat, primarily steam sterilization
Some materials e.g. plastics require low temperature sterilisation -> e.g. ethylene oxide gas used for heat and moisture sensitive medical devices

Question 8

Steam sterilization: equipment, parameters, minimum exposure period for wrapped healthcare supplies

Answer 8

Moist heat (in form of steam under pressure) is **most widely used method of sterilization. **
Uses an autoclave (basic setup shown in picture)

Four parameters:
* Steam
* Pressure
* Temperature
* Time

Principle = expose each item to direct steam contact at required temp and pressure for specified time
Recognised common minimum exposure periods for sterilization of wrapped healthcare supplies:
* 30 mins at 121 degrees C in a gravity displacement sterilizer
* 4 minutes qt 132 degrees C in a prevacuum sterilizer

Question 9

Steam sterilisation: advantages and disadvantages

Answer 9

Advantages:
* Rapidly micobicidal
* Least affected by soils
* Penetrates medical packing and device lumens
* Non-toxic
* Rapid cycle time
* Easy control or monitor of cycle
* Inexpensive

Disadvantages:
* Adverse for heat liable items
* Potential for burns

Question 10

Ethylene oxide gas sterilisation: what is it, temperature, advantages/ disadvantages

Answer 10

• Flammable colourless gas at temperatures above 10.7 degrees C
• Smels like ether at toxic levels
• Low temperature sterilant

Advantages:
* Very effective at killing micro-organisms
* Penetrates medical packaging and many plastics
* Compatible with most medical materials
* Cycle easy to control and monitor

Disadvantages
* Expensive (c.f. steam)
* Lengthy cycle/ aeration time: up to 24h (c.f. steam)
* Potential hazard to patients + staff

Question 11

Hydrogen peroxide gas plasma sterilization: advantages and disadvantages

Answer 11

Advantages:
* Used for heat and moisture sensitive items
* Compatible with most medical devices
* Fast-cycle time 28-52 minutes, no aeration necessary
* Simple to operate, install and monitor
* Safe for environment and health care worker: no toxic residuals

Disadvantages:
* Cannot process cellulose (paper), linens and liquids
* Endocopes or medical device restrictions based on lumen internal diameter and length
* Requires synthetic packaging and special container tray
* Small sterilization chamber

Question 12

Ozone sterilisation: what is ozone, effectiveness, mechanism

Answer 12

• Ozone = a gaseous molecule containing 3 oxygen atoms.
• Manufacturing: oxygen subejected to an intense electrical field that separates oxygen molecules (O2) into atomic oxygen (O), which combines with other ozygen molecules to form ozone (O3).
• Fresh ‘spring rain like’ scent, bluish color

Function
* One of the most powerful microbicides known: inactivates or kills even the most resistant pathogens
* Metastable: tendes to revert back to its original state, oxygen

Question 13

Ionizing radiation sterilization: mechanism, uses

Answer 13

• Uses gamma rays from cobalt-60 to produce sterility
• Widely used in industry: Ideal for pre-packed, heat labile, single use items e.g. needles and face masks

Question 14

Sterilization monitoring: parameters, examples of biological monitors for steam, dry heat, ETO, plasma sterilization, peracetic acid

Answer 14

• ** Physical:** cycle time, temperature, pressure
• Chemical: heat or chemical sensitive inks that change color when germicidal-related parameters are present
• **Biological: **bacillus spores that directly measure sterilization

Biological monitors:
* steam: geobacillus stearothermophilus
* dry heat, ETO: B. atrophaeus
* plasma sterilization, peracetic acid: G. stearothermophilus

Question 15

Routine decontamination methods for:
* airway
* breathing system tubing
* laryngeal masks
* self-inflating bags

Answer 15

Airway: single use disposable airways only: do not reprocess or reuse
Laryngeal masks: after use, send reusable masks to the sterile services department to be reprocessed. Should not be used >no. of times recommended by manufacturer (usually 40). Or use single-use devices instead.
Breathing system tubing: protect tubing with filters. Discard disposable single use tubing after each session of use. Ideally send reusable tubing to Sterile Services Department for cleaning and sterilization after each patient use
** Self inflating bags**: replaced by single use self inflating bags. For reusable: detergent and warm water after use.

Question 16

Routine decontamination methods for: laryngoscope, laryngoscope blades

Answer 16

Laryngoscope: cleaning then autoclaving
Laryngoscope blades: disposable blades preferred -> discard single use blades into appropriate sharps containers.

Question 17

Routine decontamination methods for: suction tubing, suction equipment

Answer 17

Suction tubing: discard disposable suction tubing after 24h continuous use, when visibly soiled, and between patients
Suction equipment: Use disposable liners and discard them when full, and between each patient, in a designated rigid container. Change suction equipment that is in use (i.e. has fluid in the container) every 48 h. Change jars after each patient. Reusable jars are for single patient use only -> rinse, clean, decontaminate using thermal disinfection or sterilization

Question 18

Routine decontamination methods for: BP cuff, tympanic thermometer, pulse oximeter

Answer 18

BP cuff: if reusable, wipe or clean with warm water and detergent between patient use
Tympanic thermometer: dispose single use earpiece covers after each use. Clean outer case with warm water and detergent or alcohol wipe
Pulse oximeter: warm water and detergent after each use

Question 19

Answer 19

Question 20

Answer 20

Question 21

Cleaning: definition, processes

Answer 21

= physical removal of the infectious material, or organic matter, on which organisms thrive.

Process may be manual or mechanical:

Manual:
* immersion in a diluted detergent at 35 degrees
* non-immersion for electrical equipment: wipe with cloth soaked in cleaning solution

Mechanical:
* can be part of thermal or chemical disinfection
* ultrasonic cleaning: used in areas that are difficult to reach. Ultrasonic waves create small bubbles on the surface. Bubbles increase in size until they cavitate and collapse -> producing areas of vacuum which dislodge the contaminants

Question 22

Commonly used methods for disinfection (4)

Answer 22

• Thermal washer disinfection
• Pasterurization (or low temperature steam)
• Boiling water disinfection
• Chemical disinfection

Question 23

Thermal washer disinfector: mechanism, suitable for, effectiveness

Answer 23

Mechanism
* Cleans devices by spraying them with water and detergent
* Initial clean at or below 35 degrees. Then hot water disinfection rince where surface temperature of devices reaches 71 degrees C for 3 minutes, 80 for 1 minute, or 90 for 1 second

Suitable for:
* Devices must be able to withstand repeated exposure to wet heat at temperatures of approx 80 degrees
* NOT suitable for hollow and porous devices unless a special adaptor is available

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

Question 24

Pasteurization: method, unsuitable for

Answer 24

• Aka low temperature steam
• Method of disinfection: >70 degrees C for 30 minutes.
• An alternative to chemical disinfection. Not a sterilization process: purpose is to destroy all pathogenic micro-organisms with the exception of bacterial spores
• Unsuitable for oily or greasy items or those with sealed cavities

Question 25

Boiling water disinfection: method, effectiveness

Answer 25

Inactivates most non-sporing micro-organisms, fungi, viruses, and some heat-sensitive spores
Should take place for at least 5 minutes for effective disinfection

Question 26

Chemical disinfectants: definition, effectiveness, precautions, examples

Answer 26

= a compond which destroys micro-organisms by chemical or physiochemical means

Effectiveness
* Can elimitate gram positive and negative bacteria
* Less effective against non-enveloped viruses, protozoal cysts and bacterial endospores

Precautions (gloves, proper ventilation) should be used to minimize exposure

Common examples:
* Alcohol
* Glutaraldehyde
* Iodophors
* etc

Question 27

Alcohols as chemical disinfectants: examples, effectiveness, concentration required, uses

Answer 27

• Most commonly used: ethyl alcohol, isopropyl alcohol
• Rapidly bacteriocidal rather than bacteriostatic, also tuberculocidal, fungicidal, virucidal
• DO NOT destroy bacterial spores - therefore not recommended for sterilizing medical and surgical materials
• Cidal activity drops sharply when diluted below 50% concentration and the optimum bactericidal concentration is in the range of 60-90% solutions in water (volume/volume)

Question 28

Glutaraldehyde as chemical disinfectant: advantages (3), uses

Answer 28

• Used as high-level disinfectant and chemical sterilant for medical equipment e.g. endoscopes, spirometry tubing, dialyzers, transducers, anaesthesia therapy equipment

Advantages:
* Excellent biocidal propeties
* Activity in the presence of organic matter
* Non-corrosive action to endoscopic equipment, thermometers, rubber or plastic equipment

Question 29

Idophors

Answer 29

• Used as both antiseptics and chemical disinfectants
• Aka iodine solutions. A combination of iodine and a solubilizing agent or carrier -> sustained-release resevoir of iodine that releases small amounts of free iodine in aqueous solution. Most common = povidone-iodine
• Bacteriocidal, mycobactericidal, virucidal
• May require prolonged contact time for certain fungi and bacterial spores

Question 30

Antiseptics: definition, effectiveness

Answer 30

= antimicrobial substances that are applied to living tissue or skin to reduce the possibility of infection.
Should generally be distinguished from antibiotics that destroy micro-organisms within the body, and from disinfectants, which destroy micro-organisms found on non-living objects.
Some are bacteriocidal, others bacteriostatic

Question 31

Disinfection method descriptions

Answer 31