What are the major and minor criteria for diagnosing endocarditis?

Major and Minor Criteria for Diagnosing Infective Endocarditis

The diagnosis of infective endocarditis is based on the Modified Duke Criteria, which classify cases as definite IE when 2 major criteria, or 1 major criterion plus 3 minor criteria, or 5 minor criteria are present. 1

Diagnostic Categories

Definite IE requires one of the following 1:

• Pathological criteria: Microorganisms demonstrated by culture or histology from vegetation, embolized vegetation, or intracardiac abscess; OR vegetation/abscess confirmed by histology showing active endocarditis
• Clinical criteria: 2 major criteria; OR 1 major criterion + 3 minor criteria; OR 5 minor criteria

Possible IE is diagnosed when 1:

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

Rejected IE applies when 1:

• Firm alternative diagnosis exists; OR
• Resolution of symptoms with ≤4 days of antibiotics; OR
• No pathological evidence at surgery/autopsy with ≤4 days of antibiotics

Major Criteria

1. Blood Cultures Positive for IE 1

Typical microorganisms from 2 separate blood cultures:

• Viridans streptococci
• Streptococcus gallolyticus (S. bovis)
• HACEK group organisms
• Staphylococcus aureus
• Community-acquired enterococci (without primary focus)

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 ≥1 hour apart)

Single positive blood culture for Coxiella burnetii OR anti-phase I IgG antibody titer >1:800 1

Critical modification: S. aureus bacteremia is now a major criterion regardless of whether it is hospital-acquired or community-acquired, and regardless of whether a removable focus exists—this represents a key update from original Duke criteria. 1, 2

2. Imaging Positive for IE 1

Echocardiogram positive for IE:

• Vegetation
• Abscess, pseudoaneurysm, intracardiac valvular perforation or aneurysm
• New partial dehiscence of prosthetic valve

Advanced imaging (ESC 2015 additions):

• Paravalvular lesions by cardiac CT 1
• Abnormal activity around prosthetic valve by ¹⁸F-FDG PET/CT (only if prosthesis implanted >3 months) or radiolabeled leukocyte SPECT/CT 1

Minor Criteria 1

1. Predisposition: Predisposing heart condition or injection drug use

2. Fever: Temperature ≥38°C

3. Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, infectious (mycotic) aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions

   • ESC 2015 addition: Silent embolic events or infectious aneurysms detected by imaging only (cerebral MRI, whole-body CT) 1

4. Immunological phenomena: Glomerulonephritis, Osler's nodes, Roth's spots, rheumatoid factor

5. Microbiological evidence: Positive blood culture not meeting major criterion OR serological evidence of active infection with organism consistent with IE

Key Clinical Pitfalls

Blood culture timing is critical: The most common cause of culture-negative endocarditis is prior antibiotic administration—63% of patients in one series had received antibiotics before cultures were obtained. 3 For non-acutely ill patients, withhold antibiotics for ≥48 hours to improve diagnostic yield. 4

Echocardiography strategy: TEE is recommended for prosthetic valves, complicated IE, or when TTE is inadequate, as TEE detects vegetations in >95% of cases versus 60-75% for TTE. 1 The minor criterion "echocardiogram consistent with IE but not meeting major criterion" has been eliminated given widespread TEE availability. 2

Culture-negative endocarditis: When blood cultures remain negative despite clinical suspicion, consider serological testing for Coxiella burnetii, Bartonella, Brucella, Legionella, and Tropheryma whipplei. 1 Q fever serology (anti-phase I IgG >1:800) was upgraded to a major criterion after studies showed 20% of pathologically confirmed Q fever endocarditis cases were misclassified as "possible" when serology was only a minor criterion. 5, 2

The scarcity of classic Osler manifestations (bacteremia, fever, peripheral stigmata) in modern practice makes diagnosis challenging—immunologic phenomena are increasingly rare, particularly in acute presentations and right-sided endocarditis. 1, 3