L42: Disinfection, Sterilisation, Infection Control

Question 1

Contamination definition

Answer 1

Soiling of inanimate or living objects with harmful, potentially infectious or unwanted matter

Question 2

Routes of transmission

Answer 2

1. Contact: direct / indirect
2. Droplet (1-2m, deposit on mucous membrane): cough, sneeze, aerosol-generating procedure (bronchoscopy)
3. Droplet nuclei: airborne (remain airborne for long periods, deposit in LRT and lungs)
4. Vector borne: arthropods
5. Blood borne
6. Food and water

Question 3

Microbes transmitted via Contact

Answer 3

S. aureus
S. pyogenes
C. difficile
E. coli
Hepatitis A virus
Rotavirus

Question 4

Microbes transmitted via Droplet

Answer 4

H. influenzae
N. meningitidis
Diphtheria
Pertussis
Influenza
Parainfluenza
Mumps
Rubella

Question 5

Microbes transmitted via Droplet nuclei

Answer 5

1. Measles
2. Varicella-zoster
3. M. tuberculosis
4. Small pox

Question 6

Principles of infection control

Answer 6

1. Remove the source
2. Block the route of transfer
3. Enhance patients’ resistance

Question 7

2-tiered infection control

Answer 7

Standard precautions

• hand hygiene (hand cleansing, handwashing, hygienic hand disinfection, surgical hand disinfection)
• PPE
• proper handling of sharps
• cough etiquette
• cleaning and disinfection
• body substance isolation (blood, body fluids)

Transmission-based precaution

1. Airborne:
   - airborne infection isolation room (AIIR: negative pressure)
   - increased air exchanges
   - HEPA filter
   - N95 masks
2. Droplet:
   - single patient room
   - surgical mask
3. Contact:
   - single patient room
   - PPE
   - regular cleaning and disinfection of surfaces

Question 8

Cleaning, Decontamination, Sterilization, Disinfection, Antisepsis

Answer 8

Cleaning: removal of visible soil, prerequisite for sterilization and disinfection

Decontamination: removal of pathogenic organisms

Sterilization: physical/chemical procedure to destroy ALL microbial life

Disinfection: physical/chemical procedure performed on INANIMATE objects that destroy MOST pathogenic microbes

Antisepsis: Germicide on LIVING tissue for inhibiting/destroying microbes

Question 9

Methods for sterilisation and disinfection

Answer 9

Physical:

1. Heat
   - Sterilization: autoclave, dry heat
   - Disinfection: boilers, thermal washer disinfectors
2. Radiation (ionising, UV radiation)
3. Filtration

Chemical:

1. Sterilants
   - Ethylene oxide
   - Hydrogen peroxide gas plasma
   - Gutaraldehyde
   - Formaldehyde
2. Disinfectants
   - Broad spectrum —> aldehyde, phenolics (chloroxylenol), halogens (clorox, iodophors)
   - Quaternary ammonium compound —> cetrimide
   - Alcohol —> ethanol, isopropanol, n-propanol
   - Biguanide —> chlorhexidine

Question 10

Spaulding’s classification of devices

Answer 10

Critical device: in contact with blood / sterile site —> sterilization
Semi-critical device: in contact with mucous membrane —> sterilization / high level disinfection
Non-critical device: in contact with intact skin —> low level disinfection / simple cleaning

Question 11

Level of resistance of different organisms

Answer 11

Most difficult —> easiest
Prions (disposable items / autoclave 134oC for 18 minutes)
Bacterial Spores
Mycobacteria
Parasitic cysts
Non-enveloped virus
Gram -ve
Fungi
Gram +ve
Enveloped virus