A 45-year-old man presents to the emergency department with a 1-week history of fever, chills, and chest pain. He has a history of intravenous drug use and no other past medical history. He reports a new heart murmur heard during a recent clinic visit. Vital signs show temperature 102.6°F (39.2°C), heart rate 97 beats/minute, respirations 18/min, and blood pressure 135/76 mmHg. On physical examination, a grade III/VI systolic murmur at the right sternal border is heard on cardiac auscultation. There are dark lines on his fingernails. Echocardiography shows valvular vegetations. Blood cultures grow catalase-positive and coagulase-positive gram-positive cocci in clusters.
C) Staphylococcus aureus
This patient presents with fever, a new murmur, and positive blood cultures showing gram-positive cocci in clusters which are catalase-positive and coagulase-positive, which is a clinical picture consistent with Staphylococcus aureus endocarditis. This is the most common cause of acute endocarditis in intravenous drug users, often affecting the tricuspid valve.
Answer choice A: Candida albicans, is incorrect. Candida albicans causes fungal endocarditis with large vegetations, typically in immunocompromised patients, and grows as yeast.
Answer choice B: Enterococcus faecalis, is incorrect. Enterococcus faecalis causes endocarditis in older patients or post-procedures, is a gram-positive cocci in chains, and is catalase-negative, not coagulase-positive.
Answer choice D: Staphylococcus epidermidis, is incorrect. Staphylococcus epidermidis causes subacute endocarditis on prosthetic valves, is coagulase-negative, and is less common in intravenous drug users.
Answer choice E: Streptococcus viridans, is incorrect. Streptococcus viridans causes subacute endocarditis in patients with pre-existing valve damage, is alpha-hemolytic, and grows in chains, not clusters. It is coagulase-negative.
Key Learning Point
Staphylococcus aureus is the leading cause of acute endocarditis in IV drug users. It is identified as gram-positive cocci in clusters, is catalase-positive and coagulase-positive, and often affects the tricuspid valve.
