What are the Duke criteria for diagnosing infective endocarditis?

Modified Duke Criteria for Diagnosing Infective Endocarditis

The Modified Duke Criteria classify infective endocarditis (IE) into three categories—definite, possible, or rejected—using a combination of pathological findings, blood culture results, and echocardiographic evidence, with definite IE requiring either pathological confirmation or specific combinations of major and minor clinical criteria. 1, 2

Diagnostic Categories

Definite Infective Endocarditis

Pathological Criteria:

• Microorganisms demonstrated by culture or histological examination of a vegetation, embolized vegetation, or intracardiac abscess specimen 1, 2
• Pathological lesions showing active endocarditis confirmed by histology in a vegetation or intracardiac abscess 1, 3

Clinical Criteria (any one of the following):

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

Possible Infective Endocarditis

• 1 major criterion plus 1 minor criterion 1, 2, 4
• 3 minor criteria 1, 2, 4

Rejected Infective Endocarditis

• Firm alternative diagnosis explaining the clinical findings 1, 2
• Resolution of IE syndrome with ≤4 days of antibiotic therapy 1, 2
• No pathological evidence of IE at surgery or autopsy after ≤4 days of antibiotic therapy 1, 2
• Does not 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) 2, 3
• HACEK group organisms 1, 2, 3
• Staphylococcus aureus 1, 2, 3
• Community-acquired enterococci (in the absence of a primary focus) 1, 2

Critical modification: S. aureus bacteremia is now 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, 4. This represents a key departure from the original Duke criteria and reflects real-world clinical experience 4.

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

Q fever serology (upgraded to major criterion):

• Single positive blood culture for Coxiella burnetii OR anti-phase I IgG antibody titer >1:800 1, 2, 4

This modification was made after studies demonstrated that Q fever serology reclassified many culture-negative cases from possible to definite IE 2, 5.

Echocardiographic Evidence

• Oscillating intracardiac mass on valve or supporting structures, in the 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 changing of pre-existing murmur is NOT sufficient) 1, 2, 6

Minor Criteria

• Predisposition: Predisposing heart condition or injection drug use 1, 2, 6
• Fever: Temperature ≥38°C 1, 3, 6
• Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions 1, 2, 6
• Immunologic phenomena: Glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor 1, 2, 6
• Microbiological evidence: Positive blood culture that does not meet a 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, 2, 6

Important modification: The echocardiographic minor criterion from the original Duke criteria has been eliminated given the widespread use of transesophageal echocardiography (TEE) 1, 4.

Diagnostic Workflow

• Transthoracic echocardiography (TTE) should be performed first in all patients with suspected IE 2
• TEE is recommended for prosthetic valves, complicated IE, or when TTE is non-diagnostic 6
• Draw 3 blood cultures by separate venipunctures on the first day; if no growth by second day, obtain 2-3 more 6
• For severely ill patients, perform 3 separate venipunctures over 1-2 hours and initiate empirical antibiotic therapy 6
• For non-acutely ill patients with negative cultures, withhold antibiotics for ≥48 hours to improve diagnostic yield 6

Diagnostic Performance and Limitations

The Modified Duke Criteria demonstrate 80% sensitivity with high specificity across diverse patient populations, including adults, pediatrics, injection drug users, and patients with both native and prosthetic valves 2, 3. However, sensitivity at admission is only 29.5%, rising to 77.5% at discharge, emphasizing that the criteria improve with length of hospitalization and serial testing 7.

Critical pitfall: Approximately 24% of patients with pathologically proven IE remain misclassified as "possible IE" despite using the Modified Duke Criteria, especially in cases of culture-negative endocarditis and when prior antibiotic therapy has been administered 5. Blood culture remains the cornerstone of diagnosis, and failure to obtain adequate cultures before antibiotic administration is a major cause of culture-negative endocarditis 6.

Clinical Judgment Override

The Duke criteria guide diagnosis but do not replace clinical judgment—treatment decisions may be made irrespective of whether criteria are met, particularly when clinical suspicion remains high despite not meeting formal criteria 1, 2. The criteria were designed for epidemiological studies and clinical trials but should be applied flexibly in individual patient management 1.