A 56-year-old man is having intermittent fevers and malaise for the past 2 weeks. He has no other localizing symptoms. Two months ago, he had valve replacement surgery for a bicuspid aortic valve. A mechanical valve was inserted and his postoperative course was uncomplicated. On examination, his temperature is 38degC, blood pressure 124/80 mm Hg, pulse 72/min, and head and neck are normal. There is a 3/6 systolic ejection murmur, the second heart sound is mechanical, and a 2/6 early diastolic murmur is heard. The lungs are clear and the skin examination is normal. Three sets of blood cultures are drawn and an urgent echocardiogram is ordered. Which of the following is the most likely causative organism?
S. epidermidis is still the leading cause of prosthetic valve endocarditis in the early post-operative period (usually defined < 2 months). It is usually the consequence of intraoperative contamination or postoperative bacteremia. Endocarditis occurring 12 months after surgery is usually due to the same organisms that cause native valve endocarditis.
Staphylococcus aureus
S. epidermidis
S. viridans
enterococci
Infection