Staphylococcus aureus bacteremia

Background

Classification

• Community-onset: positive blood culture obtained within 48 hours of presentation
• Nosocomial: positive blood culture obtained after 48 hours of presentation

Etiology

• IVDU
• Poor dentition
• Dental work

Clinical Manifestations

• Often non-specific fevers and chills, diagnosed on blood cultures
• May have back pain unrelated to spinal osteomyelitis
• May present with focus of metastatic disease

Investigations

• Repeat blood cultures every 24 to 48 hours until negative
• Transthoracic echo (TTE) or transesophageal echo (TEE)
  • A modern TTE that is good-quality and shows normal valves is quite good, though TEE is still better
  • TEE is strongly suggested in certain cases:
    • Cerebral or peripheral emboli
    • Meningitis
    • Implantable cardiac device or prosthetic heart valve
    • Prior infective endocarditis
    • Native valve disease
    • Injection drug use
    • Persistent bacteremia beyond 72 hours

Management

• Infectious diseases consultation
• Must rule out endocarditis! TTE, followed by TEE if suspicion remains high
• Low risk for endocarditis (no TEE) if all of the following:
  • No intracardiac device
  • Sterile follow-up blood cultures within 4 days from the initial set
  • No hemodialysis
  • Nosocomial acquisition of S. aureus
  • Absence of secondary foci
  • No clinical signs of endocarditis
• Uncomplicated if
  • Endocarditis is excluded
  • No implanted prostheses
  • Blood cultures clear by 2-4 days
  • Defervesces within 72 hours
  • No evidence of metastases
  • +/- identified source has been removed
• Two-week course acceptable if uncomplicated, otherwise 4-6 weeks
• MSSA: cloxacillin 2g IV q4h for 2 weeks (cefazolin as an alternative)
• MRSA: vancomycin 1g IV q12h for 2 weeks
  • Adjust based on serum trough before every fourth dose
  • Target trough 15-20

Prognosis

• Mortality 20-50% at 30 days, 60% at 1 year
• Mortality halved by ID consult
• Prognosis worse with
  • Increased age
  • Female sex
  • Pneumonia or source unknown
  • Dementia
  • Increasing comorbidities
  • Shock at time of presentation
  • Institutionalized patient