Disinfection and sterilisation

Question 1

What is the definition of disinfection

Answer 1

Destruction or removal of all or nearly all pathogens, but NOT all microorganisms

(Not absolute)

Question 2

Define sterilisation

Answer 2

Destruction or removal of all microorganisms

absolute - no viable microorganisms present

Question 3

Define decontamination

Answer 3

It is a combination of processes carried out to render a contaminated reusable medical device safe to use again

Question 4

What are the 3 categories of IC risk related to decon?

Answer 4

Critical, semi-critical, non-critical

Question 5

What is cross contamination?

Answer 5

It is when a microorganism is transmitted from one place/person to another in the same healthcare environment

Question 6

What are the 6 factors required for cross-contamination to take place?

Answer 6

• Infectious agent
• Reservoir - people, equipment, water
• Portals of exit - excretions, secretions, droplets, skin
• Means of transmission - direct contact/fomites, injection, ingestion, airborne, aerosols
• Portal of entry - broken skin, mucous membrane, GI, resp, urinary tract
• Susceptible host - neonates, diabetics, immunosuppressed, CV disease etc

Question 7

What infectious agents may be transmissible during healthcare procedures? (6)

Answer 7

Bacteria (MRSA, legionella etc)

Viruses (HBV, HCV, HIV, Herpes, COVID)

Fungi (C. Albicans)

Prions (vCJD- Variant Creutzfeldt–Jakob disease)

Protozoa

Helminths

Question 8

What are ‘reservoirs’

Answer 8

They are areas where microorganisms can reside ad proliferate - within people, environments, instruments and equipment

Question 9

Give 4 examples of portal of exit in a dental healthcare setting

Answer 9

Aerosol
Injection
Splatter
Contact

Question 10

Name the 5 mechanisms of cross contamination (infection)

Answer 10

1. Direct contact (infectious agent transmission from same or different person)
2. Indirect contact (via instruments and equipment)
3. Inhaled/airborne (DUWLs, sneezing, coughing etc)
4. Ingested (food, water hygiene)
5. Vector (clothing, towels, insects, animal contact etc)

Question 11

Which of these is involved in disinfection?

Chemical
Thermal
Irradiation

Answer 11

Chemical and thermal

Question 12

Which of these is involved in sterilisation?

Chemical
Thermal
Irradiation

Answer 12

All of them

Question 13

Outline the modifying factors for effective disinfection and sterilisation (4)

Answer 13

Nature of the microorganism: virus vs spores
Level of contamination: bio-load
Environmental conditions: moisture, temperature
Nature of the equipment to be decon: material, complexity

Question 14

What are the 4 stages of a cycle in an automated washer-disinfector?

Answer 14

1. Cool rinse at 35C
2. Hot wash at 55C
3. Thermal disinfect at 93C
4. Forced air drying

(95% + efficiency)

Question 15

What are the 2 types of irradiation that can be used for sterilisation?

Answer 15

1. Non-ionising: UV

2. Ionising: x-rays, gamma rays, electron beams

Question 16

What are the chemical types used in sterilisation?

Answer 16

Liquid - formaldehyde, hydrogen peroxide, glutaraldehyde

Gas - ethylene oxide, nitrogen dioxide, ozone

Question 17

Outline the 2 different ways thermal energy can be used in sterilisation

Answer 17

1. Direct (instrument flaming, incineration)

2. Indirect (particulate (glass bead), dry (hot air oven), moist (steam autoclave))

Question 18

Outline the parameters for autoclave sterilisation

Answer 18

(121C) 134-137C

3 minutes minimum (18 minutes)

2.2-2.5 bar pressure

Question 19

Name the 3 different types of autoclave

Answer 19

N type
B type
S type

Question 20

Which type of autoclave is non-vacuum?

Answer 20

N type (downward displacement)

Question 21

Outline what an N type autoclave would be used to sterilise

Answer 21

Solid, non-porous and unwrapped, un-pouched instruments only

Question 22

Which type of autoclave is vacuum?

Answer 22

B type

forced air removal

Question 23

Outline what B type autoclaves would be used to sterilise

Answer 23

Wrapped, pouched, porous (air-retentive) materials and instruments

Question 24

What would an S type autoclave be used for?

Answer 24

They are used for specific decontamination, e.g. endoscopes, dental handpiece sterilisation

Question 25

Give a general outline of an autoclave cycle (3 phases)

Answer 25

Heat and remove air
Hold for 3 mins at that pressure and temp
Cool and dry