Management of 2 Staphylococcus Species in Blood Cultures
Do not initiate treatment based solely on a single positive blood culture for coagulase-negative staphylococci (CoNS), as this typically represents contamination rather than true infection. 1
Initial Assessment and Culture Interpretation
The critical first step is determining whether you have true bacteremia versus contamination:
- A single blood culture positive for CoNS should be dismissed as a contaminant if a second set of blood cultures drawn simultaneously is negative 1
- If multiple blood cultures (≥2 separate draws) are positive for CoNS, this suggests true bacteremia requiring treatment 1
- The presence of 2 different Staph species raises the possibility of either polymicrobial infection or mixed contamination—repeat blood cultures immediately to clarify 1
When to Treat CoNS Bacteremia
Treatment should be initiated for CoNS bacteremia only when multiple blood cultures are positive AND the patient meets specific clinical criteria: 1
- Disease severity (hemodynamic instability, sepsis)
- Immunosuppression status
- Presence of indwelling central venous catheters or prosthetic devices
- Antibacterial resistance pattern
In adults and children (excluding neonates), remove central and arterial lines if several blood cultures are positive for methicillin-resistant CoNS (MRCoNS) 1
Empirical Antibiotic Selection
If true bacteremia is confirmed and treatment is warranted, vancomycin 15-20 mg/kg IV every 8-12 hours is the first-line agent for empirical coverage of both methicillin-resistant S. aureus (MRSA) and CoNS 1, 2
Alternative IV Options if Vancomycin Cannot Be Used:
- Daptomycin 6 mg/kg IV once daily (FDA-approved for S. aureus bacteremia; some experts recommend 8-10 mg/kg for complicated infections) 1, 3
- Linezolid 600 mg IV twice daily (excellent alternative with proven efficacy) 1
Critical Pitfall to Avoid:
Never use vancomycin as definitive therapy if methicillin-susceptible S. aureus (MSSA) is identified—this is associated with 2-3 times higher mortality compared to beta-lactam therapy 4, 5
Definitive Therapy Based on Final Culture Results
If MSSA is Identified:
Immediately switch from vancomycin to a beta-lactam antibiotic: 4, 5
- Nafcillin or oxacillin 2 g IV every 4 hours (preferred for serious infections) 6
- Cefazolin 2 g IV every 8 hours (acceptable alternative) 4, 6
The empirical combination of vancomycin PLUS a beta-lactam (nafcillin, oxacillin, or cefazolin) from the outset may improve outcomes by ensuring adequate coverage regardless of methicillin susceptibility, though this increases cost and adverse event risk 5
If MRSA or MRCoNS is Confirmed:
Continue vancomycin with target trough levels of 15-20 mg/L to achieve AUC:MIC ratio ≥400 2
For MRSA with vancomycin MIC >1 mg/L, consider alternative therapy: 1
Treatment Duration
For uncomplicated bacteremia (no endocarditis, no prosthetic devices, negative repeat cultures at 2-4 days, defervescence within 72 hours, no metastatic infection): 1
- Minimum 2 weeks of IV therapy
For complicated bacteremia (any of the above criteria not met): 1
- 4-6 weeks of IV therapy depending on extent of infection
Essential Monitoring
Obtain repeat blood cultures 2-4 days after initial positive cultures and as needed thereafter to document clearance of bacteremia 1
Perform echocardiography (preferably transesophageal) for all adult patients with S. aureus bacteremia to evaluate for endocarditis 1
Conduct clinical assessment to identify and eliminate/debride the source of infection 1
Special Consideration for Neutropenic Patients
In neutropenic cancer patients, vancomycin is NOT part of standard empirical therapy for fever and neutropenia 1
Add vancomycin only if: 1
- Hemodynamic instability or severe sepsis
- Positive blood culture for gram-positive bacteria before final identification
- Clinically suspected catheter-related infection
- Known colonization with MRSA
Discontinue vancomycin after 2-3 days if susceptible bacteria are not recovered 1