Infective Endocarditis for Step 1: Organisms, Signs & Duke

Creator: Progress Note
Published: 2026-05-19
Keywords: infective endocarditis Duke criteria, infective endocarditis usmle, endocarditis organisms, janeway lesions osler nodes, acute vs subacute endocarditis, tricuspid endocarditis iv drug use, duke criteria, streptococcus gallolyticus colon cancer, libman sacks, endocarditis prophylaxis

bolt The 60-second version

check_circleStaphylococcus aureus: most common overall; acute, destructive disease; injection drug use (tricuspid valve) and prosthetic valves.
check_circleViridans streptococci: subacute disease on previously damaged valves, often after dental work; make dextran to stick to fibrin-platelet clots.
check_circleStaphylococcus epidermidis: prosthetic valves and devices. Enterococcus: after GI or GU procedures. Streptococcus gallolyticus (bovis): look for colon cancer.
check_circleSigns: fever, new murmur, splinter hemorrhages, Janeway lesions (painless, septic emboli), Osler nodes (painful, immune complexes), Roth spots, and glomerulonephritis.
check_circleDiagnosis: modified Duke criteria — multiple positive blood cultures and echocardiographic evidence (transesophageal is more sensitive).
check_circleProphylaxis before dental procedures is only for high-risk conditions (prosthetic valve, prior endocarditis, certain congenital heart disease).

target What you'll be able to do · aligned to USMLE Step 1 · Cardiovascular System

MICROMatch endocarditis organisms to clinical settings.
CVDistinguish acute and subacute endocarditis.
CVExplain the embolic and immunologic signs of endocarditis.
CVOutline diagnosis, treatment, prophylaxis, and rheumatic fever.

How endocarditis is tested on Step 1

The setting predicts the organism.

Organisms. The mitral valve is affected most often overall; the tricuspid valve in injection drug use (septic emboli to the lungs).

Acute vs subacute. Subacute disease produces more immune-complex signs (Osler nodes, Roth spots, glomerulonephritis).

Clinical findings

Embolic and immunologic signs.

Finding	Mechanism	Description
Janeway lesions	Septic microemboli	Painless red macules on palms and soles
Osler nodes	Immune complexes	Painful nodules on finger and toe pads
Roth spots	Immune complexes	Retinal hemorrhages with pale centers
Splinter hemorrhages	Microemboli	Linear streaks under the nails
Glomerulonephritis	Immune complex deposition	Hematuria, red cell casts
Septic emboli	Vegetation fragments	Stroke, splenic or kidney infarcts; lung abscesses (right-sided)

Anemia and an elevated ESR are common in subacute disease.

Diagnosis, treatment, and prevention

Culture before antibiotics.

Blood cultures: at least three sets from separate sites before antibiotics.
Echocardiography: transthoracic first; transesophageal for prosthetic valves or when suspicion stays high.
Treatment: weeks of IV bactericidal antibiotics, starting empirically with vancomycin and narrowing by culture. Surgery for heart failure, abscess, large vegetations, embolism, or fungal infection.
Prophylaxis: amoxicillin before dental work only for high-risk cardiac conditions.

Noninfectious vegetations and rheumatic fever

Sterile vegetations and immune heart damage.

Libman-Sacks endocarditis: sterile vegetations on both sides of the valve in lupus.
Nonbacterial thrombotic (marantic) endocarditis: sterile vegetations in advanced cancer (especially mucinous adenocarcinoma) and hypercoagulable states.
Acute rheumatic fever: follows untreated group A streptococcal pharyngitis; antibodies to M protein cross-react with heart tissue (type II). Carditis with Aschoff bodies; chronic disease causes mitral stenosis. Prevent with penicillin.

Worked example

Combine the setting and the valve.

functions Worked example — fever and lung nodules

A 30-year-old who injects drugs has fever and a holosystolic murmur at the left lower sternal border that increases with inspiration. Chest CT shows multiple cavitating nodules. What is the likely organism and valve?

Injection drug use introduces skin bacteria into the venous system.
A murmur that increases with inspiration comes from the right heart; this is tricuspid regurgitation.
Vegetations on the tricuspid valve send septic emboli to the lungs, causing cavitating nodules.
Staphylococcus aureus is the most common cause in this setting.

Answer. Staphylococcus aureus tricuspid valve endocarditis.

Next in the roadmap

Pneumonia & HIV

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quiz Test yourself

Quick check — 3 questions

1. Weeks of low fever after a dental extraction in a patient with mitral valve prolapse suggests:

2. Endocarditis on a 2-month-old prosthetic valve is most often caused by:

3. Sterile vegetations on both sides of the mitral valve in a patient with lupus are:

Frequently asked questions

What is the most common cause of infective endocarditis?expand_more

Staphylococcus aureus.

How do Janeway lesions differ from Osler nodes?expand_more

Janeway lesions are painless embolic macules on palms and soles; Osler nodes are painful immune-complex nodules on finger pads.

Why should Streptococcus gallolyticus endocarditis prompt a colonoscopy?expand_more

It is associated with colorectal cancer.

Which valve is most often affected in injection drug users?expand_more

The tricuspid valve.

References & further reading

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