What are the Duke criteria for diagnosing infective endocarditis and what is the recommended treatment approach?

Duke Criteria for Diagnosing Infective Endocarditis and Treatment Approach

The Modified Duke Criteria are the gold standard for diagnosing infective endocarditis (IE), requiring either pathological confirmation or clinical criteria consisting of 2 major criteria, 1 major and 3 minor criteria, or 5 minor criteria for definite IE diagnosis, with appropriate antimicrobial therapy guided by the causative organism. 1

Modified Duke Criteria for Diagnosing IE

Diagnostic Categories

• Definite IE is diagnosed when either of the following is present:

  • Pathological criteria:
    • Microorganisms demonstrated by culture or histological examination of a vegetation, embolized vegetation, or intracardiac abscess specimen; OR
    • Pathological lesions: vegetation or intracardiac abscess confirmed by histological examination showing active endocarditis 1
  • Clinical criteria:
    • 2 major criteria; OR
    • 1 major criterion and 3 minor criteria; OR
    • 5 minor criteria 1

• Possible IE is diagnosed when:

  • 1 major criterion and 1 minor criterion; OR
  • 3 minor criteria 1

• Rejected IE is diagnosed when:

  • Firm alternative diagnosis explaining evidence of IE; OR
  • Resolution of IE syndrome with antibiotic therapy for ≤4 days; OR
  • No pathological evidence of IE at surgery or autopsy with antibiotic therapy for ≤4 days; OR
  • Does not meet criteria for possible IE as noted above 1

Major Criteria

1. Blood culture positive for IE:

   • Typical microorganisms consistent with IE from 2 separate blood cultures: Viridans streptococci, Streptococcus bovis, HACEK group, Staphylococcus aureus, or community-acquired enterococci in the absence of a primary focus 1
   • Microorganisms consistent with IE from persistently positive blood cultures: at least 2 positive cultures of blood samples drawn >12 hours apart; or all of 3 or a majority of 4 separate cultures of blood (with first and last sample drawn at least 1 hour apart) 1, 2
   • Single positive blood culture for Coxiella burnetii or anti-phase 1 IgG antibody titer >1:800 1

2. Evidence of endocardial involvement:

   • Echocardiogram positive for IE (TEE recommended for patients with prosthetic valves, rated at least "possible IE" by clinical criteria, or complicated IE with paravalvular abscess; TTE as first test in other patients) showing:
     • Oscillating intracardiac mass on valve or supporting structures, in the path of regurgitant jets, or on implanted material in the absence of an alternative anatomic explanation; OR
     • Abscess; OR
     • New partial dehiscence of prosthetic valve; OR
     • New valvular regurgitation (worsening or changing of preexisting murmur not sufficient) 1

Minor Criteria

1. Predisposition: predisposing heart condition or intravenous drug use 1, 2
2. Fever: temperature ≥38°C 1, 2
3. Vascular phenomena: major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, and Janeway's lesions 1, 2
4. Immunologic phenomena: glomerulonephritis, Osler's nodes, Roth's spots, and rheumatoid factor 1, 2
5. Microbiological evidence: positive blood culture but does not meet a major criterion or serological evidence of active infection with organism consistent with IE 1, 2

Diagnostic Approach

Blood Cultures

• Obtain at least 3 sets of blood cultures from separate venipuncture sites, with the first and last samples drawn at least 1 hour apart 1, 2
• For severely ill patients, obtain 3 separate venipunctures over 1-2 hours before initiating empirical antibiotic therapy 2
• If possible, withhold antibiotics for ≥48 hours in non-acutely ill patients with negative cultures to improve diagnostic yield 2, 3

Echocardiography

• Perform TTE as the initial imaging test in all suspected cases of IE 1
• Proceed to TEE if:
  • TTE is negative but clinical suspicion remains high
  • Prosthetic valve is present
  • Complications such as paravalvular abscess are suspected
  • Patient has poor echocardiographic windows due to obesity, chronic lung disease, or previous thoracic surgery 1

Treatment Approach for IE

Antimicrobial Therapy

• For highly penicillin-susceptible viridans group streptococci and Streptococcus bovis:

  • Aqueous crystalline penicillin G sodium 12-18 million U per 24 h IV either continuously or in 4-6 equally divided doses for 4 weeks; OR
  • Ceftriaxone sodium 2 g per 24 h IV/IM in 1 dose for 4 weeks 1
  • Alternative 2-week regimen (for selected cases): Penicillin or ceftriaxone plus gentamicin 3 mg/kg/day for 2 weeks 1
  • For penicillin-allergic patients: Vancomycin 30 mg/kg/day IV in 2 equally divided doses for 4 weeks 1

• For Staphylococcus aureus and enterococci:

  • Treatment regimens should be tailored based on antimicrobial susceptibility testing
  • Longer courses (minimum 6 weeks) are typically required for prosthetic valve endocarditis 1

Surgical Intervention

• Consider early surgical intervention for:
  • Heart failure due to valve dysfunction
  • Uncontrolled infection (persistent bacteremia, abscess, etc.)
  • Prevention of embolic events (large vegetations >10 mm)
  • Prosthetic valve endocarditis, especially with complications 1

Common Pitfalls and Caveats

• Blood cultures remain the cornerstone of diagnosis; failure to obtain adequate cultures before antibiotic administration is a major cause of culture-negative endocarditis 2, 3
• The presence of a central venous catheter may prolong bacteremia, potentially requiring catheter removal 2
• S. aureus bacteremia should be considered a major criterion regardless of whether the infection is nosocomial or community-acquired, as this modification improved diagnostic sensitivity 1
• The Duke criteria continue to hold value in the accurate assessment of IE even with technological advancements, but diagnosis may be delayed as sensitivity improves with length of hospitalization 4, 3
• For suspected culture-negative IE, consultation with microbiology laboratory or infectious disease specialists is recommended for guidance on molecular pathogen identification and serological testing 2, 5