Infective Endocarditis — Duke Criteria, Organisms & Treatment

Creator: Progress Note
Published: 2026-07-22
Keywords: infective endocarditis Duke criteria, endocarditis organisms USMLE, endocarditis treatment, HACEK endocarditis, Duke criteria major minor criteria

The 60-second version

Duke criteria: 2 major OR 1 major + 3 minor OR 5 minor = definite IE
Strep viridans: native valve (dental); S. aureus: IVDU (tricuspid) + prosthetic + acute
Strep bovis/S. gallolyticus IE: always colonoscopy to rule out colorectal cancer
Osler nodes: painful (immune complex); Janeway lesions: painless (septic emboli)
New AV block in IE = paravalvular abscess extending to conduction system → urgent surgery

Duke Criteria for Diagnosis

Definite IE: 2 major criteria, OR 1 major + 3 minor, OR 5 minor criteria. Major criteria: (1) Positive blood cultures: ≥2 separate cultures with typical IE organism (Strep viridans, S. aureus, enterococci, HACEK group) OR persistently positive cultures (3/3 or majority of ≥4 drawn >12h apart). (2) Echocardiographic evidence: oscillating intracardiac mass (vegetation), abscess, or new partial dehiscence of prosthetic valve. New regurgitant murmur (not just change in existing murmur). Minor criteria: predisposing heart condition or IVDU, fever >38°C, vascular phenomena (major emboli, septic pulmonary infarcts, mycotic aneurysm, Janeway lesions), immunologic phenomena (glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor), positive blood cultures not meeting major criteria.

Organisms by Clinical Scenario

Streptococcus viridans: most common overall (native valve); associated with dental procedures, poor dentition. Staphylococcus aureus: most common overall in IVDU; right-sided endocarditis (tricuspid valve — IVDU inject into veins → right heart first); most common in healthcare-associated IE and on prosthetic valves. S. aureus is also most common cause of ACUTE endocarditis (rapid valve destruction). Enterococcus faecalis: GI/GU procedures, elderly men (BPH + instrumentation), colorectal cancer (Strep bovis/gallolyticus IE also associated with colonic malignancy — colonoscopy mandatory). HACEK group (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella): gram-negative, oral flora, subacute course, large vegetations, typically native valves, endocarditis in dental disease patients. Streptococcus bovis (S. gallolyticus): associated with colorectal cancer — all patients need colonoscopy. Fungi (Candida, Aspergillus): IV drug users, prosthetic valves, immunocompromised — very difficult to treat; requires surgery.

Clinical Features and Treatment

Peripheral stigmata: Osler nodes (painful, tender raised lesions on finger/toe pads — immune complex deposition), Janeway lesions (painless, macular hemorrhagic lesions on palms/soles — septic emboli), Roth spots (retinal hemorrhages with white center — vasculitis), splinter hemorrhages (dark linear nail bed lines), clubbing (chronic endocarditis). Complications: septic emboli (stroke, renal infarct, splenic infarct, septic pulmonary emboli in right-sided IE), valve destruction/regurgitation → acute HF, paravalvular abscess (persistent bacteremia or new AV block on ECG → extend infection to conduction system near AV node), mycotic aneurysm (cerebral). Treatment: S. viridans and S. bovis native valve: IV penicillin G or ceftriaxone × 4 weeks. S. aureus native valve (MSSA): nafcillin or oxacillin × 6 weeks; if MRSA: vancomycin × 6 weeks (or daptomycin). Enterococcus: ampicillin + gentamicin (synergy) or ampicillin + ceftriaxone. Surgical indications: valve failure → HF, persistent bacteremia >5–7 days, abscess/fistula, fungal IE, prosthetic valve IE with complications, large mobile vegetations >10mm.

Test yourself

Quick check — 2 questions

1. A 30-year-old IV heroin user presents with fever, pleuritic chest pain, and bilateral pulmonary nodules on CT. Blood cultures grow S. aureus × 3/3. Echocardiography most likely shows vegetation on which valve?

2. A 65-year-old man is diagnosed with Streptococcus gallolyticus (bovis) endocarditis. In addition to treating the endocarditis, what additional workup is mandatory?

Frequently asked questions

Why does IV drug use preferentially cause tricuspid valve endocarditis?

Intravenous drug users inject bacteria-contaminated material directly into the venous system. Blood from peripheral veins returns to the right heart (right atrium → right ventricle → pulmonary artery) before reaching the left heart. Bacteria seed the tricuspid valve (and less commonly pulmonic) during this passage through the right heart before reaching the lungs. The tricuspid valve is normally a low-pressure, slow-flow valve — vegetations on it cause septic pulmonary emboli (bilateral patchy pulmonary infiltrates on CXR). S. aureus is the most common organism.

When is surgery indicated in infective endocarditis?

Surgical indications: (1) Acute HF from valve dysfunction (most common indication — aortic or mitral regurgitation causing cardiogenic shock or pulmonary edema); (2) Paravalvular abscess or intracardiac fistula (persistently positive blood cultures + new AV block on ECG); (3) Persistent bacteremia despite ≥5–7 days of appropriate antibiotics; (4) Fungal endocarditis (cannot sterilize with antibiotics alone); (5) Prosthetic valve IE with complications; (6) Large mobile vegetation >10mm especially with embolic events; (7) Relapsing IE with same organism despite initial cure.

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