S. aureus Bacteriaemia

Question 1

S. aureus

Answer 1

Most virulent
Causes disease through both TOXIN MEDIATED + NON-TOXIN MEDIATED MECHANISMS

HAI/COMMUNITITY ACQUIRED

GRAM +VE COCCI present in NORMAL HUMAN FLORA

Question 2

S. aureus colonisation

Answer 2

• COLONISATION RATE HIGHER = among pt. w/ IDDM, HIV INFECTION, undergoing HAEMODIALYSIS, SKIN DAMAGE
  
  • ANTERIOR NARES = most freq. site of colonisation
  • SKIN (esp. when damaged), VAGINA, AXILLA, PERINEUM, OROPHARYNX can also be colonised
  • COLONISATION SITES are RESERVOIRS for FUTURE INFECTIONS - colonisation greater risk for future infections

Question 3

Classification

Answer 3

• ENVIRONMENT of ACQUISITION = HAI/COMMUNITY ACQUIRED

* ABSENCE/PRESENCE of INDENTIFIED ASS. SITES of INFECTION = PRIMARY/SECONDARY

Question 4

Spectrum of Infection

Answer 4

• SKIN + SOFT TISSUE INFECTIONS (most commonly identified agent)
  
  • LOCALISED PYOGENIC STAPHYLOCOCCAL INFECTIONS - FURUNCLES + CARBUNCLES
  • DEEP-SEATED ABSCESSES, NECROTISING FASCIITIS, PYOMYOSITIS
  • OSTEOMYELITIS, SEPTIC ARTHRITIS, DISCITIS
  • INFECTIVE ENDOCARDITIS
  • PNEUMONIA, EMPYAEMA
  • In HOSPITAL SETTING = WOUND INFECTION, VASCULAR LINE, CATHETER-RELATED INFECTION

APPROX. 1/3 PT. w/ S. aureus bacteriaemia develop LOCAL COMPLICATIONS/DISTANT SEPTIC METASTASES

Question 5

Frequent sites of distant metastases

Answer 5

• BONES + JOINTS esp. when prosthetic materials are present
  
  • EPIDURAL SPACE + IV DISCS
  • NATIVE + PROSTHETIC CARDIAC VALVES, CARDIAC DEVICES
  • VISCERAL ABSCESSES in SPLEEN, KIDNEYS, LUNGS

Question 6

Investigations

Answer 6

Bloods:

MULTIPLE BLOOD CULTURES

• BEFORE STARTING ANTIBIOTICS + REPEAT BLOOD CULTURES 48 - 72 HRS AFTER STARTING ANTIBIOTICS

Imaging:

• X-RAY
• CT
• MRI
• RADIONUCLIDE IMAGING
• TRANSTHORACIC ECHO
TRANSOESOPHAGEAL ECHO

Other:

• MICROSCOPY + CULTURE of SPECIMENS
• BIOPSY SAMPLES - may be useful for BONE INFECTIONS

Question 7

Management

Answer 7

Antibiotic therapy

• FLUCLOXACILLIN - minimum duration of rx for UNCOMPLICATED S. aureus bacteriaemia is 14 DAYS, PENICILLIN
• VANCOMYCIN - not ideal as POOR TISSUE PENETRATION, SLOW BACTERICIDAL ACTIVITY, INCONVENIENT ADMINISTRATION, SIDE-EFFECTS, GLYCOPEPTIDE
• TEICOPLANIN - ADVANTAGE as SINGLE DAILY DOSING + can be used 3x WEEKLY AFTER APPROPRIATE LOADING, GLYCOPEPTIDE (similar to vancomycin)
• LINEZOLID - BACTERIOSTATIC, GOOD PENETRATION into BONE + EXCELLENT ORAL BIOAVAILABILITY, SYNTHETIC OXAZOLIDINONE
• DAPTOMYCIN - RAPID BACTERICIDAL activity against S. aureus, WELL-TOLERATES, ONCE DAILY DOSING, CYCLIC LIPOPEPTIDE

SOURCE IDENTIFICATION + CLEARANCE

APPROPRIATE SURGICAL INTERVENTION