A Case of Rapid Development of Methicillin‑Resistant Staphylococcus aureus Mechanical Aortic Root Abscess Despite Appropriate Antibiotic Use.

A 74-year-old male with a past medical history of mechanical aortic valve replacement presented with abdominal pain and fever. Blood cultures revealed methicillin-resistant Staphylococcus aureus (MRSA) and the patient was started on target antibiotics. Initial transthoracic echocardiogram and transesophageal echocardiogram (TEE) did not show any vegetations or significant valvular regurgitation. No other sources of infection were identified. Five days after the initial TEE, a repeat TEE revealed new areas of thickening and echolucency seen anterior to the mechanical aortic valve, suggestive of aortic root abscess (AoRA). It also extended down the mitral-aortic intervalvular fibrosa and was associated with mitral valvular vegetation.  Due to worsening clinical status and persistent bacteremia on appropriate antibiotics, a high index of suspicion for infective endocarditis (IE) remained after the initial TEE. As such, the repeat TEE was obtained only five days after and demonstrated clear evidence of rapidly growing endocarditis and abscess formation. This case uniquely demonstrates how rapid MRSA endocarditis may progress and emphasizes its high mortality. This case highlights the importance of a low threshold for repeat imaging when the index of suspicion for endocarditis remains high despite negative imaging.