Aggregatibacter aphrophilus bacteraemia with suspected infective endocarditis in a patient with bioprosthetic aortic valve replacement and atrial septal defect repair.

Introduction. Despite the established pathogenicity of Aggregatibacter aphrophilus, few clinical cases have been described in published literature. A. aphrophilus is a rare cause of prosthetic valve endocarditis and diagnosis is challenging based on nonspecific symptoms on presentation. High clinical suspicion for infective endocarditis is warranted in patients with cardiac prosthetic material and positive blood cultures. Poor dentition and dental procedures, along with other risk factors, are associated with A. aphrophilus bacteraemia. We describe a case of A. aphrophilus bacteraemia in which the diagnosis of infective endocarditis was complicated by equivocal echocardiographic findings and an initially challenging Gram stain interpretation. Case Presentation. A 59-year-old male patient with a history of bioprosthetic aortic valve replacement, atrial septal defect repair and remote dental cleaning presented to the emergency department with persistent high fevers, headaches and lethargy. Initial blood cultures were drawn and were positive for 'Gram-positive organisms', but specific morphology was challenging to determine. Subsequent testing, including MALDI-TOF, confirmed the growth of A. aphrophilus. Conclusion. Rapid identification of A. aphrophilus and recognition of the potential for infective endocarditis are paramount to ensuring adequate treatment initiation and success. This case highlights the diagnostic difficulty associated with initial Gram stain interpretation of this fastidious organism.