Sterilisation and Disinfection

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Sterilisation and Disinfection
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Factors affecting spread of infection

• Infectivity of organism
• - cant change
• Susceptibility of population
• - medical and social
• - long to medium term interventions
• Level of exposure
• - interrupt chain of transmission
• - decontaminate (lower exposure)

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Decontamination
physical or chemical process
reservoirs vectors vehicles
Microorganisms eliminate inhibit reduce
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Decontamination

• cidal process - kills organisms
• static process - inhibits growth
• For example, some disinfectants are viricidal
  but only bacteristatic

Sterilization
Disinfection
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Factors affecting Decontamination

• Microbial susceptibility - spores
• Number of microorganisms - cleaning
• Concentration or dose - temperature
• Length of exposure - surfaces
• Environmental conditions - cleaning

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Endospores Mycobacterium (Tb) Non lipid viruses
(polio) Fungi Normal bacteria Lipid viruses
(HIV, Hep B)
Decreasing resistance to disinfectants
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Heat

• Dry heat and moist heat kill cells differently
• Moist heat is MORE effective
• Heat killing is TIME and TEMP dependant.

Moist heat 15 mins at 121 C
Dry heat 6 hrs at 121 C
Milk pasteurization
3 secs at 114 C
15 secs at 72 C
30 mins at 63 C
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Autoclave

• Principle is to use moist heat (steam) under
  pressure to achieve sterilization.
• 121 C at 15 lb/in for 15 minutes (136/3)
• Penetration of the steam is CRITICAL
• - pre-evacuation of air.
• - steam removal and drying
• Entire cycle may take 40 mins to an hour.

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Monitoring autoclaves

• Heat tape - it got hot, big deal
• Temperature probes and charts - better.
• Spore strip challenges - are best
• - quarantine stock
• How often do you test ?
• Quality control
• Quality assurance

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Other physical methods

• Radiation - gamma rays
• - heat sensitive materials
• Filtration - liquids and gases
• - pore sizes and thickness
• - face masks
• - HEPA

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Chemical decontamination

• Most chemical treatments DO NOT sterilize, but if
  it is necessary, you use
• High concentration
• Noxious agents
• Need to do post disinfection removal.
• Glutaraldehyde
• Ethylene oxide
• Hydrogen peroxide

Problems with penetration - a last resort option
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Chemical Disinfectants

• Very widely used (with ignorance?)
• Toxicity versus efficiency
• Spectrum of activity
• - High, intermediate and low level
• Phenolics, quat ammonium, iodine, alcohols,
  chlorine, chlorhaxidine.
• CAUTION - spectrum
• - limited shelf life
• - dilution and inactivation

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Decontamination

• MAKE AN INFORMED CHOICE
• What level of decontamination?
• Effect on my object?
• Effect of conditions on the process?