Active infective endocarditis due to methicillin-resistant Staphylococcus aureus in the acute phase of infectious mononucleosis.

A 26-year-old male was treated for acute hepatitis due to Epstein-Barr virus and infectious mononucleosis in our hospital. At 2 weeks after admission, there was relapse with high fever. A blood culture detected methicillin-resistant Staphylococcus aureus. A two-dimensional echocardiogram revealed severe aortic regurgitation and vegetation on the left coronary cusp of the aortic valve. The diagnosis was active infective endocarditis due to methicillin-resistant Staphylococcus aureus in the acute phase of infectious mononucleosis. Following preoperative administration of vancomycin, the aortic valve was replaced with a Carbomedics prosthetic valve. The aortic valve was bicuspid, and the right cusp and non-coronary cusp were conjoined. As the focus of infection was localized to the left coronary cusp, the infected tissue was fully removed with resection of all the cusps. Although fever persisted long after the operation, the blood culture became negatransesophageal echocardiogram showed no prosthetic valve infection. Vancomycin was administered until the C-reactive protein became negative at 45 days after the operation.