What are the modified Duke criteria for diagnosing infective endocarditis?

Modified Duke Criteria for Infective Endocarditis

The modified Duke criteria remain the primary diagnostic schema for infective endocarditis, with the 2015 ESC enhancements adding cardiac CT, PET/CT imaging, and silent embolic events to improve diagnostic sensitivity, particularly for prosthetic valve and device-related infections. 1

Diagnostic Classification

The diagnosis is categorized into three groups based on pathological or clinical criteria 1:

Definite IE

• 2 major criteria, OR
• 1 major criterion + 3 minor criteria, OR
• 5 minor criteria 1
• Pathological confirmation: Microorganisms demonstrated by culture or histology from vegetation, embolized vegetation, or intracardiac abscess; OR active endocarditis on histological examination 1

Possible IE

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

Rejected IE

• Firm alternate diagnosis, OR
• Resolution of symptoms with ≤4 days of antibiotics, OR
• No pathological evidence at surgery/autopsy with ≤4 days of antibiotics, OR
• Does not meet criteria for possible IE 1

Major Criteria

1. Blood Cultures Positive for IE

Typical organisms from 2 separate blood cultures: 1

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

Persistently positive blood cultures: 1

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

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

2. Imaging Positive for IE

Echocardiography showing: 1

• Oscillating intracardiac mass on valve or supporting structures, in path of regurgitant jets, or on implanted material (without alternative anatomic explanation)
• Abscess
• Pseudoaneurysm
• Intracardiac fistula
• New partial dehiscence of prosthetic valve
• New valvular regurgitation (worsening or changing of pre-existing murmur is NOT sufficient)

2015 ESC additions to major criteria: 1

• Paravalvular lesions detected by cardiac CT
• Abnormal activity around prosthetic valve on ¹⁸F-FDG PET/CT (only if prosthesis implanted >3 months) OR radiolabelled leucocyte SPECT/CT

Minor Criteria

• Predisposition: Predisposing heart condition or injection drug use 1

• Fever: Temperature ≥38°C 1

• Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions 1

• Immunological phenomena: Glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor 1

• 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

• 2015 ESC addition: Recent embolic events or infectious aneurysms detected by imaging only (silent events) 1

Critical Diagnostic Approach

Obtain ≥3 sets of blood cultures from separate venipuncture sites before initiating antibiotics, with first and last samples drawn ≥1 hour apart 2. Blood cultures should be incubated under both aerobic and anaerobic conditions 2.

Perform transthoracic echocardiography (TTE) first in all suspected cases 2. Proceed immediately to transesophageal echocardiography (TEE) if: 2

• TTE is negative but clinical suspicion remains high
• Prosthetic valve is present
• Intracardiac device leads are present
• Optimal TTE windows cannot be obtained

Repeat echocardiography 7-10 days later if initially negative but clinical suspicion persists, or earlier if S. aureus infection is suspected 2.

Important Clinical Caveats

The modified Duke criteria have approximately 80% sensitivity when evaluated at end of follow-up, but lower diagnostic accuracy for early diagnosis, particularly in prosthetic valve endocarditis and pacemaker/defibrillator lead IE where echocardiography is normal or inconclusive in up to 30% of cases 1.

Prior antibiotic administration is the most common cause of blood culture-negative IE 2. In one prospective study, antibiotic treatment prior to blood culture was recorded in 63% of patients, and 71% had blood culture-negative IE 3.

The Duke criteria are meant to guide diagnosis but must not replace clinical judgment—clinicians may appropriately decide to treat regardless of whether criteria are met 1, 2.

The echocardiographic minor criterion was eliminated because of widespread use of TEE, which provides definitive major criterion evidence 1.

For blood culture-negative IE at 48 hours with persistent clinical suspicion, pursue specialized serological testing for Coxiella burnetii, Bartonella spp., Brucella spp., Mycoplasma spp., and Legionella spp., along with molecular diagnostics 2.