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
• Associated with about 30% mortality1

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
  • Can also use VIRSTA score to decide if they need TEE2
    • Highest sensitivity (~99%), though specificity only 35%
    • The high sensitivity gives very high negative predictive value of ~99%
    • Likely preferred to others like the PREDICT score, which has lower sensitivity though higher specificity3

Management

• Infectious diseases consultation
• Must rule out endocarditis! TTE, followed by TEE if suspicion remains high (see PREDICT score)
  • 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
    • Absence of secondary foci
    • No clinical signs of endocarditis
  • Uncomplicated if all of the following:
    • 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