A 25-year-old IV drug user presents with fever, rigors, and a new pansystolic murmur at the tricuspid area. Blood cultures taken on two separate occasions grow Staphylococcus aureus. Transthoracic echocardiography confirms large tricuspid vegetations. Which feature distinguishes S. aureus endocarditis bacteremia from transient bacteremia in terms of clinical management?

• A Persistent S. aureus bacteremia (>72 hours on appropriate antibiotics) mandates TEE and search for metastatic foci ✓
• B A single positive blood culture for S. aureus is always contaminant and requires no treatment
• C S. aureus endocarditis is always treated with oral antibiotics after 48 hours of defervescence
• D Tricuspid endocarditis requires immediate surgical valve replacement regardless of response to antibiotics

Explanation

S. aureus bacteremia is never dismissed as a contaminant — it requires minimum 14 days of IV antibiotics for uncomplicated bacteremia and 6 weeks for endocarditis. Persistent bacteremia (positive blood cultures >72 hours despite appropriate therapy) is a critical red flag for endocarditis, undrained foci (abscess, septic emboli), or device-related infection requiring escalated workup including TEE (more sensitive than TTE for vegetations) and imaging for metastatic seeding (vertebral osteomyelitis, psoas abscess, septic emboli). Uncomplicated right-sided (tricuspid) S. aureus endocarditis in IVDU can be treated with 2 weeks of IV therapy if criteria are met, not always requiring surgery.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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