What is the treatment for Staphylococcus (S.) aureus in blood culture?

Treatment of Staphylococcus aureus Bacteremia

For Staphylococcus aureus bacteremia, treatment requires intravenous antibiotics with vancomycin or daptomycin for MRSA, or cefazolin/anti-staphylococcal penicillin for MSSA, for at least 2 weeks in uncomplicated cases and 4-6 weeks in complicated cases, along with prompt removal of infected catheters and source control. 1, 2

Initial Assessment and Classification

Diagnostic Workup

• Obtain follow-up blood cultures 2-4 days after initial positive cultures to document clearance 1
• Perform echocardiography for all patients with S. aureus bacteremia 1
  • Transesophageal echocardiography (TEE) is preferred due to superior sensitivity 1
  • If TEE is performed, it should be done 5-7 days after onset of bacteremia to minimize false-negative results 1
• Conduct clinical assessment to identify source and extent of infection 1

Classification of Bacteremia

Classify as either:

1. Uncomplicated bacteremia (all criteria must be met):

   • Exclusion of endocarditis
   • No implanted prostheses
   • Negative follow-up blood cultures at 2-4 days
   • Defervescence within 72 hours of starting effective therapy
   • No evidence of metastatic sites of infection 1, 2

2. Complicated bacteremia (any of the following):

   • Positive blood cultures beyond 48-72 hours
   • Persistent fever
   • Evidence of metastatic infection
   • Implanted prostheses
   • Endocarditis 1, 2

Antimicrobial Treatment

For Methicillin-Susceptible S. aureus (MSSA)

• First-line: Cefazolin or anti-staphylococcal penicillin (flucloxacillin, dicloxacillin) 2, 3
• Duration:
  • Uncomplicated bacteremia: 2 weeks minimum 1, 2
  • Complicated bacteremia: 4-6 weeks 1, 2

For Methicillin-Resistant S. aureus (MRSA)

• First-line: Vancomycin IV or daptomycin 6 mg/kg IV once daily 1, 4
  • Some experts recommend higher daptomycin dosages (8-10 mg/kg/day) 1
• Duration:
  • Uncomplicated bacteremia: 2 weeks minimum 1, 2
  • Complicated bacteremia: 4-6 weeks 1, 2
  • Infective endocarditis: 6 weeks 1

Important Treatment Considerations

• Addition of gentamicin to vancomycin is NOT recommended for bacteremia or native valve endocarditis 1
• Addition of rifampin to vancomycin is NOT recommended for bacteremia or native valve endocarditis 1
• For persistent MRSA bacteremia, combination therapy with daptomycin + ceftaroline may be considered 1, 2

Source Control

Source control is critical for successful treatment 5:

• Remove infected intravascular catheters immediately for S. aureus bacteremia 1
• Drain abscesses and purulent collections 1
• Perform surgical debridement when necessary 1
• For long-term catheters infected with S. aureus, removal is recommended unless there are major contraindications 1

Special Situations

Catheter-Related Bloodstream Infections (CRBSI)

• Short-term catheters should be removed immediately 1
• If a long-term catheter must be retained (rare circumstance):
  • Provide systemic and antibiotic lock therapy for 4 weeks
  • Consider catheter guidewire exchange with an antimicrobial-impregnated catheter 1

Pediatric Considerations

• For children with S. aureus bacteremia:
  • IV vancomycin is recommended 1
  • If stable without ongoing bacteremia, clindamycin 10-13 mg/kg/dose IV every 6-8 hours can be used if clindamycin resistance is low (<10%) 1
  • Linezolid is an alternative for children >12 years (600 mg PO/IV twice daily) or <12 years (10 mg/kg/dose every 8 hours) 1

Monitoring Response to Treatment

• Obtain follow-up blood cultures 2-4 days after initial positive cultures and as needed thereafter 1
• Persistent bacteremia (≥48 hours) is associated with a 90-day mortality risk of 39% 5
• If fever or bacteremia persists ≥3 days after catheter removal and appropriate antibiotics, obtain additional TEE 1
• After catheter removal due to S. aureus CRBSI, placement of a new catheter should proceed only when additional blood cultures show no growth 1

Common Pitfalls and Caveats

• Short-course therapy risk: Treatment <14 days is associated with increased risk of relapse 6
• Primary bacteremia caution: Even with low risk of complications, primary bacteremia should not receive short-course therapy due to poor prognosis 6
• Rapid diagnostics importance: Early determination of staphylococcal species and antibiotic susceptibility facilitates earlier appropriate treatment and reduces unnecessary antibiotic use 7
• Transthoracic echocardiography limitation: TTE findings alone are insufficient to rule out infective endocarditis 1

By following this structured approach to S. aureus bacteremia management, focusing on appropriate antibiotic selection, adequate duration, and thorough source control, you can optimize patient outcomes and reduce the risk of complications.