Lecture 9 Controlling Microbes 1 Aims of lecture

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Lecture 9Controlling Microbes 1 Aims of lecture

• To define the terms
• sterilization
• disinfection
• decontamination
• antisepsis
• To understand the meaning of nosocomial infections

• To understand the principles and methods of
  sterilization
• To become aware of some agents used as
  disinfectants
• Some added notes on the assignment

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Sterilization defined

• A physical or chemical process used to destroy or
  remove all forms of life
• In the health care context it means killing all
  microbial life forms including including spores

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Disinfection defined

• A process directed at killing pathogens
• The process is less lethal than sterilization
  (eg. may not kill all spores)
• The process is not a substitute for sterilization
  and has a reduced a safety margin
• Tends to refer to inanimate objects

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Decontamination

• A process which renders a device, instrument,
  environmental surface safe to handle or contact
• In the clinical setting this does not necessarily
  mean the instrument is safe to reuse

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Antisepsis defined

• The process of topical application of a chemical
  which can be tolerated without injury on living
  tissue
• The process is not the same as disinfection-the
  latter term tends to refer to inanimate objects

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Nosocomial infections

• This term will be revisited later in the course
• In general refers to infections which are
  acquired by patients which were not present or
  incubating prior to admission
• Generally accepted to arise at least 48 hours
  post admission, but can include infections
  developing after discharge eg s/wound

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Sterilization in detail1. Efficiency of
sterilization

• Sterilization is an all/or nothing process
  either an item is sterile or not
• In reality there is always the chance that a
  contaminant may survive a process
• The efficiency of a sterilization process is
  often related to the degree of severity of
  treatment eg length of exposure to heat
• The process effectiveness must be validated

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The sterilizer

• Several process are available
• Depends on the item being sterilized, eg
• Autoclave(heat under pressure)
• Ethylene oxide (for heat labile items)
• Gamma radiation (plastics)
• Gluteraldehyde?? (endoscopes)

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Confidence in the process

• In practice not possible to guarantee that
  everything has been killed
• Tend to talk about the probability of survival
  eg. 11000 1 1,000,000
• Certain items eg surgical instruments may need
  confidence levels in range 1106

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How doe we get confidence
106 Bacterial numbers 105 104 103 102 10 10-1 10-2
10-3 10-4 10-5 10-6
0 1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16 17
18 TIME (min)
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Monitoring efficiency

• Use controls
• Usually place very resistant life forms in the
  process- if they survive process has failed
• eg Bacillus stereothermophilus spores
• Temperature gauges
• Chemical autoclave tapes- change colour

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Heat sterilization

• Dry and wet heat can be used
• Dry heat cheaper-but less reliable
• Microbes vary enormously in their capacity to
  resist heat
• Heats main effect degradation of organic matter
  esp proteins

• Examples of heat tolerance
• M. tuberculosis 65-100oC
• T. aquaticus gt 75oC
• L. monocytogenes 70oC
• Fungi viruses 60-100oC
• HIV 60oC 30 min
• HBV gt80oC
• Prions gt134oC moist 18 min
• Spores gt 100oC

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Autoclaving

• Steam under pressure
• Steam can be heated gt 100oC if under pressure
• Heat in steam gt 100oC is called latent heat
• When hot steam touches cooler item latent heat
  released
• Instrument called an autoclave

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The steam autoclave
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Disinfectants(usually aqueous)

• Alcohols
• Generally 70 in water (better penetration)
• Evaporate at RT
• No residue
• Short acting
• Flammable
• Not effective HIV

• Aldehydes
• 1-2 active
• Toxic
• Carcinogenic?
• Good antiviral
• Active against spores
• Active against HIV at higher concentration

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Disinfectants contin...

• Chlorhexidine
• Can be diluted in alcOH
• Effective at 0.2-1
• Generally non toxic
• Often used as antiseptic

• Chlorine
• Na hyperchlorate
• Can be irritant
• Corrosive
• Effective against HBV and HIV
• Needs to be fresh and at recommended

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Disinfectant contin...

• Phenols
• Toxic irritants
• Strong disinfectant
• General purpose hospital disinfectant
• Odourless forms now more in use

• Ammonium compounds
• Soluble in water
• Low spectrum of activity
• Generally non toxic low grade household
  disinfectant

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Susceptibility of microbes to disinfection

• Susceptibility variable
• In some cases microbes can grow in disinfectants
• Mycobacteria (TB) need a detergent to penetrate
  waxy coat
• Bacterial spores aldehydes and halogens if high
  

• Viruses aldehydes and halogens eg HBV HIV with
  2 glut or 1 available chlorine
• Fungi agents usually fungistatic rather than
  fungicidal- aldehydes have some activity

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A few notes on the essay

• The essay should contain discussion of control
  measures relevant at the
• bedside
• Ward
• Hospital
• Intra hospital levels

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Some of the items you may want to discuss at each
level

• Bed level
• Handwashing
• Standard precautions
• Additional precautions
• Management of catheterization and other invasive
  devices
• Wound care and surveillance
• Patient monitoring

• Patient isolation
• Intubator maintenance
• Respirator maintenance
• Other equipment
• Cleaning
• Waste
• Vaccination prophylaxis

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• Ward level
• Infection control outbreak protocols (eg MRSA)
• Patient cohorting
• Ward design airflow
• Recording infections notification and
  surveillance
• Infection control teams

• Education basic and continuing inservice
• Notifiable disease requirements eg HIV, HBV, STDs
• Implementation of protocols and education
  programs
• Education of visitors
• Education of support staff

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• Hospital level
• Infection control Committee
• Policy determination
• funding for continuing programs
• Recording and reporting infection rates
• Surveillance programs
• Educational program design review
• Review processes
• Standards practitioner IC accreditation

• Intrahospital level
• Patient screening incoming and outgoing eg MRSA,
  GRGNs
• Information gathering, updating eg VRE worl wide
• Conference attendance
• Workshops
• Professional associations