A 35-year-old intravenous drug user presents with fever, septic pulmonary emboli on CT, and a systolic murmur loudest at the right sternal edge that increases with inspiration. Echo shows a tricuspid valve vegetation. The most common causative organism of right-sided infective endocarditis in IVDU is:
- A Streptococcus viridans
- B Staphylococcus aureus ✓
- C Enterococcus faecalis
- D Candida albicans
Correct answer: B. Staphylococcus aureus
Explanation
Staphylococcus aureus (usually methicillin-sensitive or MRSA) is responsible for >50% of infective endocarditis cases in intravenous drug users, and it predominantly causes right-sided (tricuspid valve) endocarditis. S. aureus bacteremia is highly virulent, adheres avidly to previously normal valves, and spreads hematogenously, causing septic pulmonary emboli characteristic of tricuspid IE. Streptococcus viridans causes left-sided IE predominantly in patients with pre-existing valve disease. Enterococcus and fungi are less common causes in IVDU.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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