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大綱

Sterilization & disinfection Dr Irene Hui

Introduction To prevent transmission of infection by elimination of micro-organisms from contaminated instruments, equipments, environments or other items Decontamination of equipment, instruments or environment Handling of spills Waste disposal Quality control

Terms Sterilization Complete killing or removal of all types of micro-organisms, including spores Disinfection Reduce the number of viable micro-organisms on a surface or in a load May not necessarily inactivate spores Different levels of disinfection

Terms Sterilant Chemical compounds which can kill sporing bacteria under controlled conditions Disinfectant Chemical agent which can destroy vegetative micro-organisms and viruses Antiseptic Disinfectant applied to skin or living tissue

Sterilization Methods Heat sterilization: Moist heat vs Dry heat Incineration Chemical sterilant E.g. ethylene oxide, glutaraldehyde, and peracetic acid Exposure to moist heat is the most reliable & controllable method

Autoclave Downward displacement Steam admitted into upper part of the chamber push air downwards Suitable for simple unwrapped instruments Porous load sterilizer Air effectively removed from a sealed chamber and the load by vacuum before steam admission For sterilization of porous loads Sterilization cycle 121°C x15 mins 134°C x 4 mins

Monitoring of autoclave Keep temperature & pressure records for each cycle Chemical indicators: ‘processed’ ≠ sterilized Biological indicators: spore test Other tests / monitoring as required Refer to manufacturers instructions and recommendations Regular maintenance

Glutaraldehyde ‘cidex’ Effective vs vegetative organisms, spores, viruses, & fungi Relatively slow vs mycobacteria 2% alkaline glutaraldehyde activated at alkaline pH 7.5 to 8.5 Long exposure time required for sporicidal activity Non-damaging to metals, plastics, rubber Irritant to eyes, skin, respiratory tract

Disinfection-Heat Heat more reliable than chemical methods 100°C for 10 mins à disinfect reliably Beware of risk of scalding

Disinfection-Chemical methods Pre-cleaning Presence of organic material Type & number of micro-organisms Exposure time Concentration of disinfectants Physical configuration of the object (Crevices, hinges, lumens) Avoid bubbles during immersion in disinfectants Temperature & pH

Resistance to disinfectants Prions Bacterial spores Mycobacteria Nonlipid or small viruses Fungi Vegetative Bacteria Lipid or medium sized viruses

Disinfectants Halogens Alcohol Phenolics Peroxygen Formaldehyde

Halogens - Chlorine releasing agents 1 “Chlorox” Rapidly effective vs viruses, fungi, bacteria and spores Cheap Readily inactivated by organic matter Corrosive especially when high concentration are used Incompatible with some detergents Activity decreases as pH increases

Halogens - Chlorine releasing agents 2 Solutions Unstable à Prepare fresh solution daily Solid Sodium dichloroisocyanurate (NaDCC) tablets, powders or granules E.g. ‘Haztab’ Advantage: stable during storage and allow accurate preparation of solutions Applications Disinfection of compatible instruments & equipments Environmental disinfectants Disinfection of spillage

Alcohol 70% ethyl alcohol (ethanol) & 60-70% isopropyl alcohol (isopropanol) Effective vs most viruses but not hydrophilic viruses (e.g. echovirus, coxsackievirus) Not active vs mycobacteria & spores Effective & rapid Inactivated by organic matter Coagulate & precipitate proteins à Do not apply to proteinaceous materials Poor penetrating power à use on clean surface only (e.g. equipment surfaces) Flammable Store in cool & ventilated area Keep away from fire or sparks

Phenolics Activity Active vs mycobacteria, bacteria & fungi Active vs lipid-containing viruses but not non-lipid containing viruses Poor vs spores Cheap Not readily inactivated by organic matter Absorbed by rubber and plastic Avoid contact with skin or mucous membrane

Peroxygen “Virkon”: potassium peroxymonosulfate, sodium chloride and inorganic surfactant Supplied as a sacket granulated compound In-use-concentration, 1% Stable for 7 days or until the pink color fades Active vs bacteria and virus Ineffective vs spores Less corrosive than hypochlorite

Formaldehyde Can be generated by boiling formalin or heating of paraformaldehyde Slow acting Neutralize with ammonia Ventilate area before return to use Irritating odor Probable carcinogen Useful space decontaminants for biological safety cabinets

Storage & Use Storage Location Avoid prolong storage: Fresh preparation and frequent change Quantity Containers Do not top up disinfectant Clean and dry Clear label contents, in use dilution, and expiry date Keep covered Use Avoid overloading with contaminated items Avoid unintended dilution of disinfectants during use

Selection of disinfectants Intended use Spectrum of activity Speed of action Inactivation by organic material Compatibility Safety Stability Cost

Thank you