What are the diagnostic criteria for Infective Endocarditis (IE)?

Diagnostic Criteria for Infective Endocarditis (IE)

The diagnosis of infective endocarditis is based on the Modified Duke Criteria, which classifies cases as "definite," "possible," or "rejected" based on specific major and minor criteria. 1

Definite Infective Endocarditis

Pathological Criteria

• Microorganisms demonstrated by culture or histological examination of a vegetation, embolized vegetation, or intracardiac abscess specimen
• Pathological lesions showing active endocarditis (vegetation or intracardiac abscess confirmed by histology)

Clinical Criteria (any of the following combinations)

• 2 major criteria, or
• 1 major criterion and 3 minor criteria, or
• 5 minor criteria

Possible Infective Endocarditis

• 1 major criterion and 1 minor criterion, or
• 3 minor criteria

Rejected Infective Endocarditis

• 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

Major Criteria

1. Blood Cultures Positive for IE

• Typical microorganisms consistent with IE from 2 separate blood cultures:
  • Viridans streptococci, Streptococcus gallolyticus (formerly S. bovis)
  • HACEK group (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella)
  • Staphylococcus aureus (both community and hospital-acquired)
  • Community-acquired enterococci in the absence of a primary focus
• Persistently positive blood cultures:
  • ≥2 positive blood cultures drawn >12 hours apart, or
  • All of 3 or majority of ≥4 separate blood cultures (first and last drawn ≥1 hour apart)
• Single positive blood culture for Coxiella burnetii or phase I IgG antibody titer >1:800

2. Imaging Evidence of Endocardial Involvement

• Echocardiogram positive for IE:
  • Vegetation (mobile echogenic mass on valve or supporting structures)
  • Abscess, pseudoaneurysm, intracardiac fistula
  • Valvular perforation or aneurysm
  • New partial dehiscence of prosthetic valve
• Advanced imaging (2015 ESC criteria additions) 1:
  • Paravalvular lesions identified by cardiac CT
  • Abnormal activity around prosthetic valve detected by 18F-FDG PET/CT (if prosthesis was implanted >3 months) or radiolabeled leukocyte SPECT/CT

Minor Criteria

1. Predisposition: Predisposing heart condition or injection drug use
2. Fever: Temperature >38°C (100.4°F)
3. Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, infectious aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions
4. Immunological phenomena: Glomerulonephritis, Osler's nodes, Roth spots, rheumatoid factor
5. Microbiological evidence: Positive blood culture not meeting major criteria or serological evidence of active infection with organism consistent with IE

Important Clinical Considerations

Echocardiography

• Transesophageal echocardiography (TEE) has higher sensitivity than transthoracic echocardiography (TTE) and is recommended for:
  • Prosthetic valve patients
  • Patients with suspected complicated IE (paravalvular abscess)
  • Patients with poor quality TTE images

Culture-Negative Endocarditis

• Consider serological testing for organisms that are difficult to culture:
  • Coxiella burnetii (Q fever)
  • Bartonella species
  • Brucella species
  • Legionella species
  • Tropheryma whipplei

Diagnostic Pitfalls

• The sensitivity of Modified Duke Criteria may be lower in:
  • Prosthetic valve endocarditis
  • Right-sided endocarditis
  • Cardiac device-related endocarditis
  • Culture-negative cases due to prior antibiotic administration

Recent Advances

The 2015 ESC guidelines enhanced the Modified Duke Criteria by adding:

• Cardiac CT findings of paravalvular lesions as a major criterion
• 18F-FDG PET/CT or radiolabeled leukocyte SPECT/CT findings around prosthetic valves as a major criterion
• Silent embolic events or infectious aneurysms detected by imaging as a minor criterion 1

Recent research indicates that these modifications improve diagnostic sensitivity without significant loss of specificity, particularly in cases of prosthetic valve and device-related endocarditis 2.

The diagnostic accuracy of the Modified Duke Criteria is highest when applied at the end of patient evaluation rather than at initial presentation, as more clinical and laboratory data become available over time 3.