What are the diagnostic criteria for infective endocarditis?

Diagnostic Criteria for Infective Endocarditis

The Modified Duke Criteria are the universally accepted diagnostic standard for infective endocarditis, classifying cases as definite IE (based on pathological findings OR clinical criteria of 2 major criteria, 1 major + 3 minor criteria, or 5 minor criteria), possible IE (1 major + 1 minor criterion, or 3 minor criteria), or rejected. 1

Major Criteria

Blood Culture Criteria

• Typical microorganisms from ≥2 separate blood cultures: Viridans streptococci, Streptococcus bovis, HACEK group organisms 1
• Staphylococcus aureus bacteremia (regardless of acquisition source - community or nosocomial, with or without removable focus) 1
  • Critical modification: The original Duke criteria only counted community-acquired S. aureus, but 13-46% of nosocomial S. aureus bacteremia cases develop definite IE, necessitating this change 1
• Community-acquired enterococci in the absence of a primary focus 1
• Persistently positive blood cultures: ≥2 positive cultures drawn >12 hours apart, OR all of 3, OR majority of ≥4 separate cultures (with first and last drawn ≥1 hour apart) 1
• Single positive blood culture for Coxiella burnetii OR anti-phase I IgG antibody titer >1:800 1
  • Key modification: Originally a minor criterion, elevated to major after studies showed this reclassified culture-negative cases from "possible" to "definite" IE 1

Echocardiographic Criteria

• Oscillating intracardiac mass on valve or supporting structures, in the path of regurgitant jets, or on implanted material (without alternative anatomic explanation) 1
• Abscess (periannular or intracardiac) 1
• New partial dehiscence of prosthetic valve 1
• New valvular regurgitation (worsening or changing of preexisting murmur is NOT sufficient) 1
• TEE is recommended for prosthetic valves, cases rated "possible IE" by clinical criteria, or complicated IE; TTE should be the first test in other patients 1

Minor Criteria

• Predisposing heart condition (e.g., mitral valve prolapse, prior IE, bicuspid aortic valve, valve stenosis/insufficiency) or injection drug use 1
• Fever ≥38.0°C 1
• Vascular phenomena: major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions 1
• Immunologic phenomena: glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor 1
• Microbiological evidence: positive blood culture not meeting major criterion OR serological evidence of active infection with organism consistent with IE (excludes single positive cultures for coagulase-negative staphylococci and organisms that do not cause endocarditis) 1

Diagnostic Categories

Definite IE

Pathological criteria:

• Microorganisms demonstrated by culture or histological examination of vegetation, embolized vegetation, or intracardiac abscess specimen 1
• Pathological lesions showing active endocarditis on histological examination 1

Clinical criteria (any of the following):

• 2 major criteria 1
• 1 major criterion AND 3 minor criteria 1
• 5 minor criteria 1

Possible IE

• 1 major criterion AND 1 minor criterion 1
• 3 minor criteria 1

Rejected

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

Diagnostic Performance

The Modified Duke Criteria demonstrate 80% sensitivity with high specificity across diverse populations including adults, pediatrics, injection drug users, and patients with both native and prosthetic valves 2, 3. This represents a substantial improvement over the original Duke criteria (80% vs 51% for pathologically confirmed cases) and the older Von Reyn criteria (76% vs 56%) 3, 4.

Critical Pitfalls to Avoid

• Premature antibiotic administration: Obtain ≥3 blood culture sets from separate venipunctures BEFORE starting antibiotics; this is the most common cause of culture-negative endocarditis 5, 2
• Culture-negative cases: 24% of pathologically proven IE cases remain misclassified as "possible" despite Modified Duke Criteria, particularly with prior antibiotic therapy or Q fever IE 4
• Inadequate echocardiography: TEE has far superior sensitivity and specificity compared to TTE; failure to escalate to TEE when clinical suspicion remains high despite negative TTE leads to missed diagnoses 6, 4
• Underestimating nosocomial S. aureus: Any S. aureus bacteremia warrants consideration of IE, not just community-acquired cases 1