What are the Duke criteria for diagnosing infective endocarditis?

Duke Criteria for Diagnosing Infective Endocarditis

The Modified Duke Criteria classify infective endocarditis as definite, possible, or rejected based on combinations of major and minor clinical criteria, with definite IE diagnosed by either pathological confirmation or specific clinical combinations: 2 major criteria, 1 major + 3 minor criteria, or 5 minor criteria. 1, 2

Diagnostic Categories

Definite Infective Endocarditis

Pathological criteria:

• Microorganisms demonstrated by culture or histologic examination of vegetation, embolized vegetation, or intracardiac abscess specimen 1, 2
• Histologic evidence of active endocarditis in vegetation or intracardiac abscess 1, 2

Clinical criteria (any one of the following):

• 2 major criteria 1, 2, 3
• 1 major criterion + 3 minor criteria 1, 2, 3
• 5 minor criteria 1, 2, 3

Possible Infective Endocarditis

• 1 major criterion + 1 minor criterion 1, 2, 3
• 3 minor criteria 1, 2, 3

Rejected Infective Endocarditis

• Firm alternative diagnosis explaining the clinical findings 1, 2, 3
• Resolution of IE syndrome after ≤4 days of antibiotic therapy 1, 2, 3
• No pathological evidence at surgery or autopsy after ≤4 days of antibiotics 1, 2, 3
• Failure to meet criteria for possible IE 1, 2

Major Criteria

Blood Culture Findings

Typical microorganisms from ≥2 separate blood cultures:

• Viridans streptococci 1, 2, 3
• Streptococcus gallolyticus (formerly S. bovis) 1, 2, 3
• HACEK group organisms 1, 2, 3
• Staphylococcus aureus 1, 2, 3
• Community-acquired enterococci without a primary focus 1, 2, 3

Critical modification: S. aureus bacteremia now qualifies as a major criterion regardless of whether it is nosocomial or community-acquired, because 13–46% of hospital-acquired S. aureus bacteremia cases progress to definite IE. 2, 3 This represents a key upgrade from earlier criteria that excluded nosocomial cases.

Persistently positive blood cultures (any of the following):

• ≥2 positive cultures drawn >12 hours apart 1, 2, 3
• All 3 cultures positive 1, 2
• Majority of ≥4 separate cultures positive with first and last drawn ≥1 hour apart 1, 2

Coxiella burnetii (Q fever):

• Single positive blood culture for C. burnetii OR anti-phase I IgG titer >1:800 1, 2, 3
• This was upgraded from a minor to major criterion after studies showed it reclassifies many culture-negative cases from possible to definite IE 2, 4

Echocardiographic Evidence

Any of the following findings:

• Oscillating intracardiac mass on valve or supporting structures (in path of regurgitant jets or on implanted material) without alternative anatomic explanation 1, 2, 3
• Abscess (perivalvular or myocardial) 1, 2, 3
• New partial dehiscence of prosthetic valve 1, 2, 3
• New valvular regurgitation (worsening or change of pre-existing murmur alone is insufficient) 1, 2, 3

Imaging approach: Transthoracic echocardiography (TTE) should be performed first in all suspected cases; proceed immediately to transesophageal echocardiography (TEE) if TTE is negative but clinical suspicion remains high, prosthetic valve is present, intracardiac device leads are present, or optimal TTE windows cannot be obtained. 1, 2, 5

Minor Criteria

• Predisposition: Predisposing heart condition (mitral valve prolapse, prior IE, bicuspid aortic valve, valve stenosis/insufficiency) or injection drug use 1, 3
• Fever: Temperature ≥38°C 1, 3
• Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions 1, 2, 3
• Immunologic phenomena: Glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor 1, 3
• Microbiological evidence: Positive blood culture not meeting major criterion (excludes single positive cultures for coagulase-negative staphylococci and organisms that do not cause endocarditis) or serological evidence of active infection with organism consistent with IE 1, 3

Important note: The echocardiographic minor criterion has been eliminated from the modified criteria given widespread use of TEE. 1, 4

Diagnostic Performance and Critical Pitfalls

The Modified Duke Criteria demonstrate approximately 80% sensitivity and high specificity across diverse patient populations including adults, pediatrics, injection drug users, and patients with both native and prosthetic valves. 2, 3 However, 24% of pathologically proven IE cases may remain misclassified as "possible IE," particularly in culture-negative and Q-fever cases. 6

Critical pitfalls to avoid:

• Premature antibiotic administration is the most common cause of culture-negative IE; obtain ≥3 blood culture sets from separate venipunctures before starting antibiotics, with first and last samples drawn at least 1 hour apart. 3, 5
• Underestimating nosocomial S. aureus: Any S. aureus bacteremia should be considered a potential cause of IE regardless of acquisition source. 2, 3
• Over-reliance on criteria: The Duke criteria guide diagnosis but do not replace clinical judgment—clinicians may appropriately decide to treat regardless of whether criteria are met. 2, 5
• Inadequate repeat imaging: If initial echocardiography is negative but clinical suspicion remains high, repeat imaging 7–10 days later, or earlier if S. aureus infection is suspected. 5