Definition of Complicated Bloodstream Infection
A complicated bloodstream infection (BSI) is characterized by the presence of metastatic foci of infection, septic thrombosis, endocarditis, osteomyelitis, or other deep-seated infections, as well as persistent bacteremia despite appropriate antimicrobial therapy and source control. 1
Key Characteristics of Complicated BSIs
Defining Features
- Metastatic spread beyond the primary source - infection that proceeds beyond the original organ or site 1
- Persistent bacteremia despite appropriate antimicrobial therapy 1
- Deep-seated infections such as:
- Septic thrombosis
- Endocarditis
- Osteomyelitis
- Retinitis (especially with fungal BSIs)
- Abscesses 1
Causative Organisms Associated with Complications
- Staphylococcus aureus - high risk for metastatic complications 1
- Candida species - associated with higher mortality and treatment failure 1
- Multidrug-resistant organisms - particularly problematic in healthcare-associated BSIs 2
Differentiating Complicated vs. Uncomplicated BSIs
Uncomplicated BSIs
- Respond promptly to appropriate antimicrobial therapy
- No evidence of metastatic infection
- Often caused by coagulase-negative staphylococci (especially in catheter-related infections) 1
- Typically require shorter duration of antimicrobial therapy (5-7 days) 3
- Source is often readily identifiable and controllable 2
Complicated BSIs
- Require prolonged antimicrobial therapy (typically 14 days or longer) 1
- May require surgical intervention for source control 1
- Often involve difficult-to-treat organisms 4
- Higher mortality rates 4
Clinical Scenarios That Define Complicated BSIs
Catheter-Related Complicated BSIs
- Tunnel infection or port abscess in patients with tunneled catheters or implantable devices 1
- Septic thrombosis associated with vascular catheters 1
- Persistent positive blood cultures despite catheter removal 1
Source-Related Complications
- High-risk sources - BSIs originating from sources other than urinary tract or biliary tract (after source control) carry higher mortality risk 1
- Difficult-to-treat resistance (DTR) - resistance to all β-lactams, carbapenems, β-lactamase inhibitor combinations, and fluoroquinolones 1
Management Implications of Complicated BSIs
Treatment Duration
- Uncomplicated BSIs: 5-7 days of antimicrobial therapy 3
- Complicated BSIs:
- Septic thrombosis or endocarditis: 4-6 weeks of antimicrobial therapy
- Osteomyelitis: 6-8 weeks of antimicrobial therapy 1
Device Management
- Uncomplicated BSIs: May attempt catheter salvage in select cases (e.g., coagulase-negative staphylococci) 1
- Complicated BSIs: Require device removal in most cases, particularly with:
- Tunnel infections
- Port abscesses
- Persistent bacteremia
- Fungal infections 1
Special Considerations
Risk Factors for Developing Complicated BSIs
- Immunosuppression
- Valvular heart disease
- Presence of prosthetic materials
- Delay in appropriate antimicrobial therapy 2
- Previous antibiotic exposure 5
Diagnostic Approach for Suspected Complications
- Transesophageal echocardiography (TEE) for suspected endocarditis, especially with S. aureus BSI 1
- Appropriate imaging studies to identify metastatic foci of infection
- Regular monitoring of blood cultures to document clearance 2
Conclusion
The distinction between complicated and uncomplicated BSIs has important implications for management decisions, including duration of antimicrobial therapy, need for device removal, and follow-up investigations. Early recognition of complicated BSIs allows for appropriate intervention to improve outcomes and reduce mortality.