What are the modified Duke criteria for diagnosing infective endocarditis?

Modified Duke Criteria for Diagnosing Infective Endocarditis

The modified Duke criteria classify infective endocarditis as definite, possible, or rejected based on specific combinations of major and minor criteria: definite IE requires either pathological confirmation OR 2 major criteria, 1 major + 3 minor criteria, or 5 minor criteria. 1

Diagnostic Classification System

The Duke criteria provide a structured framework with approximately 80% sensitivity when evaluated at the end of follow-up, though diagnostic accuracy is lower for early diagnosis, particularly in prosthetic valve endocarditis and pacemaker/defibrillator lead IE 2. Clinicians must remember that these criteria guide diagnosis but do not replace clinical judgment—treatment decisions may be made irrespective of whether criteria are formally met 2, 1.

Definite Infective Endocarditis

Pathological criteria (gold standard):

• Microorganisms demonstrated by culture or histological examination of a vegetation, embolized vegetation, or intracardiac abscess specimen 1, 3
• Histologic evidence of active endocarditis in a vegetation or intracardiac abscess 1, 3

Clinical criteria (any one of the following):

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

Possible Infective Endocarditis

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

Rejected Infective Endocarditis

• Firm alternative diagnosis that explains the findings 1
• Resolution of IE syndrome after ≤4 days of antibiotic therapy 1
• Absence of pathological evidence at surgery or autopsy after ≤4 days of antibiotics 1
• Failure to meet any possible IE criteria 1

Major Criteria

Blood Culture Findings

Typical microorganisms from 2 separate blood cultures:

• Viridans streptococci, Streptococcus gallolyticus (formerly S. bovis), HACEK group organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella), or community-acquired enterococci without primary focus 1, 3
• Staphylococcus aureus bacteremia regardless of acquisition setting (nosocomial or community-acquired)—this was upgraded to major criterion because 13-46% of hospital-acquired S. aureus bacteremia cases progress to definite IE 1, 4

Persistently positive blood cultures (any one of the following):

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

Coxiella burnetii (Q fever):

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

Echocardiographic Evidence

Imaging positive for IE (any one of the following):

• Oscillating intracardiac mass on valve or supporting structures without alternative anatomic explanation (vegetation) 1, 3
• Abscess (perivalvular or myocardial) 1, 3
• New partial dehiscence of prosthetic valve 1, 3
• New valvular regurgitation (not merely worsening of pre-existing murmur) 1, 3

2015 ESC additions to major criteria:

• Paravalvular lesions detected by cardiac CT 2
• Abnormal activity around prosthetic valve on 18F-FDG PET/CT 2

Minor Criteria

• Predisposition: Predisposing heart condition or injection drug use 2, 3
• Fever: Temperature ≥38°C 2, 3
• Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhages, conjunctival hemorrhages, Janeway lesions 2, 3
• Immunologic phenomena: Glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor 2
• Microbiological evidence: Positive blood culture not meeting major criterion or serological evidence of active infection with organism consistent with IE 2

Diagnostic Workflow

Initial imaging approach:

• Perform transthoracic echocardiography (TTE) first in all suspected cases 2, 1
• 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 2
• TEE has higher sensitivity than TTE for detecting vegetations 2
• Repeat echocardiography 7-10 days later if initially negative but clinical suspicion remains high, or earlier if S. aureus infection is suspected 2

Blood culture technique:

• Obtain at least 3 sets of blood cultures from separate venipuncture sites before initiating antibiotics, with first and last samples drawn at least 1 hour apart 2
• Incubate under both aerobic and anaerobic conditions 2
• Blood cultures are positive in approximately 90% of IE cases when properly obtained 2

Critical Pitfalls

Culture-negative IE: Prior antibiotic administration is the most common cause of blood culture-negative IE 2. When blood cultures remain negative at 48 hours and clinical suspicion persists, perform specialized testing including serological testing for Coxiella burnetii, Bartonella spp., Brucella spp., Mycoplasma spp., and Legionella spp., plus molecular diagnostics 2.

Prosthetic valve and device-related infections: The modified Duke criteria have lower diagnostic accuracy for early diagnosis in these populations 2. Consider advanced imaging (cardiac CT, PET/CT) to improve sensitivity 2.

Surgical specimens: All resected valvular tissue or embolic fragments should be collected in sterile containers without fixative and sent immediately to microbiology for pathological examination, which remains the gold standard for diagnosis 2.