Sterilization and disinfection

Background

Definitions

• Cleaning is the process of removing soil and organic material, usually with water and detergents or enzymes
• Sterilization is a process that eliminates all forms of microbial life
• Disinfection is a process that eliminates many or all pathogenic microbes on inanimate objects, with the exception of spores
• Chemical sterilants are disinfectants that will kill spores with prolonged exposure (2 to 12 hours)
• High-level disinfectants will kill all microorganisms except large numbers of bacterial spores within a shorter amount of time (e.g. 20 minutes)
• Low-level disinfectants will kill most vegetative bacteria, some fungi, and some viruses within a short amount of time (e.g. 10 minutes)
• Intermediate-level disinfectants may be cidal for mycobacteria, vegetative bacteria, most viruses, and most fungi, but are not sporicidal

Sterilization

• The process of sterilization destroys all forms of microbial life
• May be physical or chemical methods
  • Steam under pressure
  • Dry heat
  • EtO gas
  • Hydrogen peroxide gas plasma
  • Liquid chemicals
• Equipment must be cleaned first, before attempting to disinfect or sterilize it

Spaulding Classification of Medical Equipment

Classification	Contact with	Processing	Examples
Critical	Sterile tissue or vascular system	Cleaning followed by sterilization	Surgical instruments, biopsy instruments, and foot care equipment
Semi-critical	Non-intact skin or mucous memranes, but not penetrating the skin	Cleaning followed by a minimum high level disinfection	Respiratory equipment, flexible endoscopes
Non-critical	Intact skin	Cleaning followed by low level disinfection	Tourniquets, BP cuffs, linen, and furniture

Rutala Modification

• Endoscopes, which secondarily enter sterile tissues, should be considered critical

Methods of Sterilization and Disinfection

Method	Corrodes Metal	Smooth, Hard Surfaces				Rubber Tubing and Catheters		Polyethylene Tubing and Catheters		Lensed Instruments		Thermometers	Hinged Instruments
		S	HLD	ILD	LLD	S	HLD	S	HLD	S	HLD	LLD	S	HLD
Heat sterilization, including steam or hot air for 3 to 30 min		X				X		X		X			X
Ethylene oxide gas for 1 to 6 hours		X				X		X		X			X
Hydrogen peroxide gas plasma for 45 to 72 minutes		X				X		X		X			X
Glutaraldehyde-based formulations (>2% gluteraldehyde) or gluteraldehyde 1.12% and phenol/phenate 1.93%		10 h	X			10 h	X	10 h	X	10 h	X		10 h	X
Hydrogen peroxide 7.5%	X	6 h	X			6 h	X	6 h	X	6 h	X		6 h	X
Peracetic acid >0.2% for 12 min at 50 to 56ºC		X				X		X		X			X
Hydrogen peroxide 7.35% and peracetic acid 0.23%, or hydrogen peroxide 1% and peracetic acid 0.08%	X	3 to 8 h	X			3 to 8 h	X	X	X	3 to 8 h	X		X	X
Ortho-phthalaldehyde (OPA) 0.55%			X				X		X		X			X
Wet pasteurization (30 min at 70ºC) with detergent cleaning			X				X		X					X
Hypochlorite generated by electrolyzing saline	X		X				X		X		X			X
Ethyl or isopropyl alcohol 70 to 90%				X	X							X
Sodium hypochlorite 5.25 to 6.15% (diluted household bleach)				X	X
Phenolic germicidal detergent solution				X	X
Iodophor germicidal detergent solution				X	X
Quaternary ammonium germicidal detergent solution					X

• Exposure times:
  • Sterilization: varies by method
  • High-level disinfection: 12 to 30 minutes at ≥20ºC
  • Intermediate disinfection: ≥1 min
  • Low-level disinfection: ≥1 min

Medical Device Reprocessing Department (MDRD)

• Needs separate areas for receiving soiled instruments, decontaminating, cleaning, sterilizing, and storing
• Treated essentially like an OR, with controlled temperature and humidity, with dedicated ventilation system
• Negative pressure in decontamination areas and positive pressure in clean areas

Pre-Cleaning

• Dismantle and sort devices, then soak them

Cleaning

• Remove all visible soil from every accessible surface
• Can use ultrasonic machines and washing machines
• Rinse to remove detergents, then dry

Sterilization

• High temperature sterilization whenever possible
• Low-temperature sterilization can be done for heat sensitive critical and semi-critical items
  • Uses gas, including hydrogen peroxide gas plasma or vapour, or ozone (but that needs 4 hours)
  • Needed for things with plastic, for example
• Liquid emersion can be done for heat sensitive crticical and semi-critical items
  • Hydrogen peroxide most common liquid

Monitoring

• Spore tests: compare a strip that went through the autoclav to a control that was held outside
• ATP system test strips

Storage

• Equipment must be stored until results are available from the spore test for that batch
• Controlled temperature and humidity

Further Reading

• APIC