Infective Endocarditis: Etiology, Symptoms, and Diagnosis

Infective Endocarditis: Etiology and Clinical Features

Etiology and Causes

Infective endocarditis (IE) is an infection of the endocardial surface of the heart, typically involving the heart valves. It is caused by microorganisms, primarily bacteria and occasionally fungi.

Common Causative Organisms

• Bacteria:
  • Staphylococcus aureus: Most common overall, especially in acute IE and IV drug users.
  • Viridans group streptococci: Common in subacute IE, especially after dental procedures.
  • Enterococci: Frequent in elderly patients or after genitourinary/gastrointestinal procedures.
  • Staphylococcus epidermidis: Often associated with prosthetic valve endocarditis.
  • HACEK organisms: Slow-growing Gram-negative bacilli (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella).
  • Streptococcus bovis (gallolyticus): Associated with colon cancer.
• Fungi:
  • Candida or Aspergillus: More common in immunocompromised patients or those with prosthetic valves and catheters.

Primary Risk Factors

• Pre-existing valve disease (e.g., rheumatic heart disease, mitral valve prolapse)
• Prosthetic heart valves
• Congenital heart defects
• Intravenous drug use
• Recent dental or surgical procedures
• Indwelling vascular catheters
• Immunosuppression

Clinical Features

The presentation can be acute (rapid onset, high-grade fever, septicemia) or subacute (gradual onset with nonspecific symptoms).

General Symptoms

• Fever and chills (most common)
• Fatigue and malaise
• Anorexia and weight loss
• Night sweats

Cardiac Manifestations

• New or changing heart murmur
• Signs of heart failure (dyspnea, edema) due to valvular dysfunction

Embolic and Immunologic Manifestations

• Janeway lesions: Painless, erythematous macules on palms and soles (septic emboli).
• Osler nodes: Painful, tender nodules on fingers or toes (immune complex deposition).
• Roth spots: Retinal hemorrhages with pale centers.
• Splinter hemorrhages: Linear hemorrhages under the fingernails.
• Petechiae: Found on skin, conjunctiva, and mucosa.
• Splenomegaly.

Embolic Complications

• Stroke or limb ischemia from emboli.
• Renal infarcts or glomerulonephritis.
• Pulmonary emboli (especially in right-sided IE from IV drug use).

Diagnostic Investigations

• Blood cultures: Multiple sets drawn before initiating antibiotics.
• Echocardiography: TTE or TEE to visualize vegetations.
• Duke Criteria: Standardized major and minor criteria for diagnosis.