Healthcare acquired infections

Question 1

What microbial factors tip the scale from colonisation to infection

Answer 1

Increased:
□ Resistance
□ Virulence
□ Transmissibility
□ Increased survival ability
□ Ability to evade host defences

Question 2

What host factors tip the scale from colonisation to infection

Answer 2

• Devices: PVC, CVC, Urinary catheter, Ventilation
• Antibiotics
• Break in skin surface
• Foreign body
• Immunosuppression
• ?Gastric acid suppression
• Age extremes
• Overcrowding
• Increased opportunity for transmission e.g. Interventions, Hands

Question 3

What are the main modes of transmission of microbes and which HAIs are largely transmitted by which route?

Answer 3

○ UTI (22.6% of all HAI) – mainly related to catheterisation
○ Surgical Site Infection (18.6%)
○ Respiratory Tract Infection (17.5%) – intubation accounted for about a quarter of these
○ Bloodstream infections (10.8%) – many Central Venous (CVC) Catheter related
○ Gastrointestinal infection (6.8% versus 15.4%)
○ Skin and soft tissue infection (4.0%)

Question 4

What is the chain of infection?

Answer 4

○ Source of microbe (endogenous or exogenous)
○ Transmission
- Direct contact
□ e.g. Staphylococcus aureus, coliforms
- Respiratory/Droplet
□ e.g. Neisseria meningitidis, Mycobacteria tuberculosis
- Faecal-Oral
□ e.g. Clostridium difficile, Salmonella sp.
- Penetrating Injury
□ e.g. Group A streptococcus, Bloodborne viruses
○ Host

Question 5

How do you break the chain of infection?

Answer 5

○ Risk awareness 
○ Standard Infection Prevention and Control Precautions (SICPs)
○ Hand Hygiene
○ Appropriate PPE
○ Vaccination 
○ Post Exposure Prophylaxis
○ Environment

Question 6

What is meant by cleaning (give examples how this is achieved)?

Answer 6

○ Physical removal of organic material and decrease in microbial load
○ Manufacturer’s instructions
○ Detergent and water
○ DRYING IS AN IMPORTANT PART OF THE PROCESS!
○ Cleaning essential PRIOR to disinfection and Sterilisation if these are required

Question 7

What is meant by disinfection (give examples how this is achieved)?

Answer 7

○ Large reduction in microbe numbers - spores may remain
○ Heat
- Pasteurisation (e.g. bedpans, linen, dishwashers)
- Boiling (vaginal specula, ear syringes)
○ Chemical
- Chemicals vary in their organism activity range
- Needs to be equipment compatible
- Examples: Alcohol, chlorhexidine, hypochlorites, hydrogen peroxide

Question 8

What is meant by sterilisation (give examples how this is achieved)?

Answer 8

○ Removal/Destruction of ALL microbes and spores
○ Steam under pressure (autoclave)
○ Hot Air Oven
○ Gas (ethylene dioxide)
○ Ionising Radiation

Question 9

What is the definition of an outbreak?

Answer 9

An outbreak of an infection is defined as 2 or more cases of an infection linked in time and place

Question 10

What are the typing methods?

Answer 10

○ Antibiogram (antibiotic sensitivity pattern)
○ Phage typing (e.g. Staphylococcus aureus)
○ Pyocin typing (Pseudomonas)
○ Serotyping (Salmonella, Pseudomonas)
○ Molecular typing (DNA typing)

Question 11

What are the control measures for outbreaks of infection?

Answer 11

○ Single room isolation
○ Cohorting of cases
○ Clinical Area/Ward Closure
○ Re-enforcement of IPC measures
○ Staff exclusion (e.g. colonised staff in case of MRSA; non-immune staff in case of VZV, measles etc.)
○ Staff decolonisation or other measures