A 40-year-old IVDU is admitted with fever, chills, and sepsis. Blood cultures grow Staphylococcus aureus. Transthoracic echo is non-diagnostic. Transoesophageal echo (TOE) reveals a 15 mm mobile vegetation on the tricuspid valve. Duke criteria are met. Per modified Duke criteria, this constitutes:
- A Definite infective endocarditis (one major + one major criterion) ✓
- B Possible infective endocarditis (one major criterion)
- C Rejected diagnosis; requires two separate positive blood cultures
- D Possible IE requiring repeat blood cultures at 48 hours
Explanation
Per the modified Duke criteria, definite IE requires two major criteria, one major + three minor, or five minor criteria. Major criteria include: (1) positive blood cultures with typical IE organisms (S. aureus is a qualifying organism in two separate blood cultures) and (2) evidence of endocardial involvement (echocardiographic vegetation, new regurgitation, abscess, or dehiscence). This patient has TWO major criteria: positive S. aureus bacteraemia and echocardiographic vegetation on TOE, meeting the threshold for definite IE. Typical organisms for one positive blood culture (e.g., Coxiella burnetti) are different criteria.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.