Staph Aureus bacteraemia

Question 1

Normal carriage of S.aureus

Answer 1

– Upper respiratory tract of 20-30% population
• 30% Nose (anterior nares)
• 20% Throat
– Skin of healthy individuals
• Hands 27%
– Perineum
• 22%

Question 2

Process of S.aureus laboratory identification

Answer 2

1. Blood cultures taken from patient and sent to
   laboratory (0-12 hours)
2. Blood culture “flags positive” (0-3 days)
3. Gram stain = Gram positive cocci in clusters. Blood inoculated onto agars (30 minutes)
4. Once growth present (12-24hours)
   1=Typical appearance of colonies
   • Coagulase test (S. aureus is coagulase positive)
   =Identification from MALDI-TOF (1 hour)
   =Antimicrobial sensitivity testing on VITEK
   (12-18 hours)

-2-4 days to final result

Question 3

Virulence factors of S.aureus examples

Answer 3

-Pyrogenic toxin superantigens
-TSST
-EFA/B
-Enterotoxins
-PVL

Question 4

Virulence factors and clinical syndromes of S.aureus

Answer 4

1. Toxic Shock Syndrome toxin
   -> Toxic shock syndrome
2. Enterotoxins
   -> Gastroenteritis
3. Exfoliative toxins (A+B)
   -> Staphylococcal Scalded Skin Syndrome
4. Panton Valentine Leucocidin
   -> Necrotising pneumonia, abscesses, severe soft
   tissue infections
   -> Should use antimicrobials with anti-toxin affect for
   PVL e.g. Clindamycin or linezolid

Question 5

What types of infection does S.aureus cause?

Answer 5

SOFT PAINS

-Skin infections (cellulitis)/ surgical site infections (wound infection)
-Osteomyelitis and septic arthritis (plus spondylodiscitis)
-Food poisoning
-Toxic shock syndrome

-Pneumonia
-Abscesses (psoas muscle/ cerebral)
-Infective endocarditis
-Necrotising fasciitis
-Scaled skin syndrome

Question 6

What are the risk factors for S.aureus bacteraemia?

Answer 6

-Loss of skin barrier
• Post surgical site infections
• History of trauma
• Chronic ulcers
– e.g. venous, arterial, neuropathic
• People who inject drugs

-Immunocompromised
• Diabetes
• Renal/Liver failure
• Immunosuppressive medications

-Prosthetic materials
• Cannula sites
• Central lines
• Prosthetic joints
• Prosthetic heart valves

Question 7

Immediate management of cellulitis

Answer 7

-Sepsis 6:

=Take: blood cultures, lactate, measure fluid balance
=Give: empirical antibiotics, fluids, oxygen if hypoxic

Question 8

Management for severe cellulitis

Answer 8

-Mark around border of erythema and limb elevation
-IV flucloxacillin 2g 6-hourly
-If penicillin allergy or risk of MRSA: IV vancomycin
-Strict fluid balance and monitoring regular observations

Question 9

Mortality and relapse rates of S.aureus bacteraemia

Answer 9

-MR: 15-25% (MSSA SAB)
-RR: 10-15%

Question 10

How long should we give antibiotics for S.aureus?

Answer 10

-Minimum 2 weeks IV therapy (reduce relapse rate)
=Longer courses required if complicated/deep site of infection
-All cases reviewed by infection specialist

Question 11

Further investigations for S.aureus bacteraemia

Answer 11

– Repeat blood cultures in 48-72 hours to ensure bacteraemia cleared
– Need to assess for deep sources of bacteraemia (back pain, swollen joints)
– Consider echocardiogram
=trans-oesophageal if trans thoracic negative and prosthetic valve/ high suspicion of endocarditis

Question 12

Sources of SAB

Answer 12

-Vascular device
-Skin/soft tissue/wound
-Septic arthritis
-Osteomyelitis
-Discitis
-Endocarditis
-Prosthesis
-Infected DVT/ septic thrombophlebitis
-Pneumonia

Question 13

Scoring systems accurate predictors of sepsis

Answer 13

NEWS >-5 and qSOFA >-2

Question 14

Monitoring progress of SAB

Answer 14

-Monitor inflammatory markers- normalisation of CRP at 2 weeks
-Repeat blood cultures are negative

Question 15

Why is MRSA an issue?

Answer 15

-Methicillin resistant S.aureus
-Alteration of the “penicillin binding proteins” which
confers resistance to most Beta Lactam antibiotics

Question 16

Risk factors for MRSA

Answer 16

-Health Protection Scotland Screening tool:
=Does the patient reside in a care home or other institutional setting /
has been transferred from another hospital?
=Has patient previously been MRSA positive?
=Does patient present with a wound, ulcer or other indwelling medical
device in-situ before this admission to hospital?
=Community acquired: history of foreign travel to an area of high risk (USA)

Question 17

Treatment for MRSA

Answer 17

-Vancomycin is the current treatment of choice for MRSA
bacteraemia.
• MRSA positive patients should be isolated in a single room and
offered decolonisation treatment.