Delayed Diagnosis of Native-Valve Infective Endocarditis Presenting as Progressive Aortic Regurgitation in Recurrent Methicillin-Sensitive Staphylococcus aureus Bacteraemia With Initially Negative TTE and FDG PET-CT

Infective endocarditis (IE) remains a life-threatening condition in which early diagnosis is essential to prevent valvular destruction and systemic complications. Persistent Staphylococcus aureus bacteraemia (SAB) is strongly associated with endocardial infection, yet diagnosis may be challenging when initial imaging is inconclusive. We describe a case of a 55-year-old woman who presented with fever, vomiting, and transient loss of consciousness. Blood cultures grew methicillin-sensitive Staphylococcus aureus (MSSA). Initial transthoracic echocardiography (TTE) and positron emission tomography-computed tomography (PET-CT) imaging failed to identify endocarditis. Despite appropriate antimicrobial therapy, she developed recurrent bacteraemia, ongoing pyrexia, and clinical deterioration. Transoesophageal echocardiography (TOE) subsequently demonstrated severe aortic regurgitation consistent with IE. Because of significant underlying liver disease, surgery was deemed prohibitive, and she was managed with prolonged intravenous antibiotics and cardiology follow-up for potential future valve intervention. This case highlights the importance of maintaining a high clinical suspicion for IE in patients with persistent SAB. It supports guideline recommendations for early TOE when clinical suspicion remains high despite a negative transthoracic study. The final Duke-International Society for Cardiovascular Infectious Diseases (ISCVID) 2023 classification of the case aligned with definite IE. The patient completed six weeks of antibiotic treatment after blood culture clearance, which was achieved at week two following the start of antibiotic therapy.