M: Sterilization, Disinfection, Infection Control - Week 8

Question 1

What do ‘aseptic technique’ and ‘infection control’ involve?

Answer 1

Aseptic technique: involves using procedures to minimise the transfer of microorganisms

Infection control: involves the prevention or minimisation of cross infections

Question 2

How do cross infections spread? (3)

Answer 2

• patient to staff
• staff to patient
• patient to patient

Question 3

How can infections be spread? (3)

Answer 3

• direct contact
• aerosol
• instrument/equipment

Question 4

When may optometrists be exposed to blood, tears and mucous membranes? (5)

Answer 4

When:
- remove a foreign body
- assessing patients with ocular trauma, conjunctivitis or microbial keratitis
- carrying out lacrimal lovage
- expressing glands and cysts
- fitting contact lenses

Question 5

List 8 communicable diseases that could potentially be passed from patient to optometrist:

Answer 5

• HIV/AIDS
• Hep B and C
• TB
• Measles, mumps, rubella, chicken pox
• infectious mononucleosis
• herpes, influenza
• Adebovirus 8
• CID

Question 6

Define the following:
A) cleaning
B) disinfection
C) sterilisation

Answer 6

A: removal of contaminating matter to reduce burden of organic material

B: removing from an article some or all of its burden of pathogenic microorganisms

C: destruction or removal of all viable microorganisms, spores and other infectious agents from an article

Question 7

Explain the 3 classifications found in the Spaulding classification system of equipment uses

Answer 7

1. Critical: invasive devices that enter normally sterile tissue or enter the vascular system by intent or accident

2: device contacts but does not penetrate mucous membrane

3: Device only contacts intact skin

Question 8

List 3 factors that influence decision making in regards to whether to sterilise or disinfect

Answer 8

1. risk and cost/benefit analysis
2. Common sense
3. Lobby groups (susceptible hosts)

Question 9

What do you need to ensure a sterilisation/disinfection process is efficient? (3)

Answer 9

1. Appropriate agent
2. Appropriate conditions
3. Appropriate apparatus (to ensure effective contact between agent and microorganisms)

Question 10

What information do you need to design a sterilisation/disinfection process? (3)

Answer 10

• initial contamination level
• rate of biocidal action of agent
• sterility assurance required

Question 11

Explain the process of obtaining a ‘Viable Count’ (5)

Answer 11

• prepare dilutions of sample
• spread on agar plates
• incubate plates
• count colonies
• estimate microbial load (one colony = one bacterial cell)

Question 12

What does the D value represent?

Answer 12

The amount of time required to kill 90% of the organisms in a sample (ie a 10-fold reduction)

Question 13

Define sterility assurance

Answer 13

A calculated probability that a microorganism could survive a sterilisation process and thereby render a proportion of treated articles unsterile

Question 14

Name the 4 main methods of sterilisation

Answer 14

1. Heat
2. Filtration
3. Ionising radiation
4. Use of chemicals

Question 15

Which heat is more effective at sterilisation: moist or dry?

Answer 15

Moist heat

Question 16

List one advantage and one disadvantage of sterilisation by heat

Answer 16

Adv: reliable, available, economical

Disadv: heat causes physical and chemical changes which denature major cell constituents such as proteins

Question 17

Explain the difference between moist and dry heat sterilisation

Answer 17

Moist heat coagulates. Dry heat oxidises

Question 18

When do you use dry heat vs moist heat for sterilisation?

Answer 18

Dry: glass, metal, cutting instruments, powders, waxes, eye ointment bases

Moist: most non-heat sensitive instruments and materials; decontamination of used articles

Question 19

List 4 advantages of dry heat sterilisation

Answer 19

• penetration of solids
• use for non-aqueous liquids
• closed cavities
• non-corrosive

Question 20

List 2 disadvantages of dry heat sterilisation

Answer 20

• long times (up to 4 hours)
• high temperatures: potentially destructive

Question 21

List 2 advantages of moist heat sterilisation

Answer 21

• rapid (esp. pre-vacuum, steam sterilisers)
• effective

Question 22

List 2 disadvantages of moist heat sterilisation

Answer 22

• corrosive over time
• wets articles (including wrapping)

Question 23

Define biocidal vs biostatic

Answer 23

Biocidal processes or agents kill microorganisms and are irreversible

Biostatic processes and agents inhibit microbial growth and are usually reversible

Question 24

How does filtration sterilise?

Answer 24

Microorganisms are removed (not killed) by a combination of adherence and exclusion — so filter maintenance is critical

Question 25

When are filters used? (2)

Answer 25

• for heat sensitive liquids, to obtain pyrogens free liquids, air
• different filters have different pore sizes ranging from 0.3 to 10um down to 10nm that are selected to exclude bacteria, mycoplasma, and, viruses

Question 26

Describe depth filter. What’s it made of ? And how is it’s flow?

Answer 26

Fibrous sheet or mat, like maze

Made of: paper, asbestos, or glass fibres

Good flow rate

Question 27

Describe membrane filter. What’s it made of? How’s the flow?

Answer 27

Large number of tiny holes, like sieve

Made of cellulose acetate or nitrate

85% space so good flow

Question 28

Describe nucleation filter. What’s it made of? How’s the flow rate?

Answer 28

Small number of holes, like mat

Made of very thin polycarbonate film, irradiated then etched

Low flow rate

Question 29

How does ionising radiation sterilise? List 3 advantages and disadvantages

Answer 29

By creating free radicals which damage DNA

Adv: effective at ambient temp, no wetting, articles packaged ready for use

Disadv: Hugh install costs, safety issues, possible deleterious effects

Question 30

What is the rate of biocidal action?

Answer 30

Involves calculating how many organisms survive the sterilisation process over time

(Or more accurately, how many organisms are killed over time)

Question 31

Provide 3 reasons why we dont just sterilise for a very long time

Answer 31

• cost
• efficiency
• could cause damage to the article/equipment

Question 32

What requires a higher sterility assurance? A bandaid or syringe?

Answer 32

Syringe

Question 33

What happens to the sterilisation process if you don’t wash the item beforehand?

Answer 33

It starts at a higher initial contamination therefore takes longer to sterilise to the amount you want

Question 34

List 4 advantages and 4 disadvantages of using chemicals in sterilisation.

Answer 34

Adv: are bactericidal, virucidal, fungicidal and sporicidal (kills spores)

Disadv: slow, expensive, toxic residues, and carcinogenic