What are the causes of septic emboli?

Causes of Septic Emboli

Septic emboli most commonly originate from right-sided endocarditis, infected intravascular catheters, and pacemaker wires, with other sources including septic thrombophlebitis from the tonsils, jugular, dental, and pelvic regions. 1

Primary Sources of Septic Emboli

Cardiovascular Sources

• Right-sided infective endocarditis

  • Most common causative organism is Staphylococcus aureus 1
  • Particularly common in intravenous drug users 1
  • Colonized intravascular catheters are the most common identified source of nosocomial endocarditis 1

• Intravascular Device-Related

  • Infected indwelling catheters (central venous catheters, peripherally inserted central catheters) [1, 1
  • Pacemaker wires and cardiovascular implantable electronic devices [1, 1
  • Vascular grafts and prostheses 1

Septic Thrombophlebitis

• Peripheral or central vein thrombophlebitis with superimposed infection 1
• Septic thrombosis of great central veins (presenting with ipsilateral neck, chest, or upper extremity swelling) 1
• Jugular vein thrombophlebitis (Lemierre's syndrome) 1
• Pelvic thrombophlebitis 1

Other Sources

• Dental infections with hematogenous spread 1
• Skin and soft tissue infections, including abscesses [2, 3
• Bone infections (osteomyelitis) 4
• Septic thrombosis due to peripheral arterial catheters 1

Microbiology of Septic Emboli

Common Pathogens

• Staphylococcus aureus - most frequent causative organism [1, 1
  • Including methicillin-resistant S. aureus (MRSA) [2, 3
• Coagulase-negative staphylococci - especially with intravascular devices [1, 1
• Gram-negative bacteria - including Pseudomonas aeruginosa 1
• Anaerobic bacteria - particularly with septic thrombophlebitis 1
• Candida species - especially in immunocompromised patients [1, 1

Changing Microbial Patterns

• Increasing incidence of anaerobic gram-positive and gram-negative bacteria and bacterioide species due to:
  • Growing population of immunocompromised patients 1
  • Increased use of indwelling catheters and vascular prostheses 1

Clinical Manifestations

Septic emboli can present with:

• High-grade, persistent bacteremia 1
• Fever, respiratory distress, and chest pain 2
• Septic pulmonary emboli with multiple, peripheral, nodular, possibly cavitated lesions on imaging 4
• Metastatic infections at distant sites 1
• Continued positive blood cultures after catheter removal (suggesting septic thrombosis) 1

Complications

• Septic pulmonary emboli [1, 2
• Mycotic aneurysms, particularly intracranial [1, 5
• End-organ abscesses (splenic, cerebral, etc.) [6, 5
• Persistent bacteremia despite source control 1
• In-hospital mortality up to 20% in some case series 4

Diagnostic Approach

1. Blood cultures - critical for identifying causative organisms 1
2. Imaging:
   • Chest X-ray or CT for pulmonary emboli 4
   • Echocardiography for endocarditis 1
   • CT or MRI for source identification and complications 5
3. Source identification - critical for management 4

Management Principles

1. Source control - removal of infected catheters, drainage of abscesses 3
2. Appropriate antimicrobial therapy - based on culture results 1
3. Surgical intervention when necessary:
   • Valve replacement for endocarditis 5
   • Splenectomy for splenic abscesses 5
   • Coiling/clipping of infectious intracranial aneurysms 5

Clinical Pitfalls and Caveats

• Blood cultures may be negative, particularly with prior antibiotic exposure 4
• Septic emboli can occur even after catheter removal due to persistent infected thrombi 1
• High index of suspicion needed in patients with risk factors even without obvious source 6
• Patients with large valve vegetations (>20mm) and elevated WBC counts have higher risk of splenic emboli requiring intervention 5
• The role of anticoagulation in septic thrombophlebitis remains undefined and potentially risky 4

Septic emboli represent a serious complication with significant morbidity and mortality. Early recognition, source identification, appropriate antimicrobial therapy, and timely intervention are essential for optimal outcomes.