<i>Citrobacter </i><i>koseri</i> Infective Endocarditis in an Immunocompetent Male Successfully Treated with Valve Replacement and a Shortened-Course of Antimicrobial Therapy: A Case Report

Background: Citrobacter koseri is a rare cause of infective endocarditis (IE), especially in immunocompetent individuals. We present a case of acute IE of the native mitral valve caused by C. koseri in a 61-year-old Filipino man successfully treated with valve replacement and shortened-course of antimicrobial therapy. Case Presentation: The patient presented with fever, delirium, cardiac symptoms, leukocytosis and elevated procalcitonin. He was given meropenem and vancomycin as empiric therapy, Blood cultures identified C. koseri. A transesophageal echocardiogram confirmed the presence of a large, mobile vegetation measuring 1.399 cm attached to the anterior mitral valve leaflet. Given the patient’s multiple risk factors for embolization, including a vegetation size greater than 10 mm, vegetation mobility, vegetation location on the anterior mitral valve leaflet, and the possibility of prior embolization, the patient underwent a successful valve replacement. Vegetation attached to the anterior mitral valve leaflet was visualized intraoperatively. There was no paravalvular extension of infection, annular abscess, or destructive penetrating lesion (fistula). Postoperatively, fever lysed, and inflammatory markers improved. Postoperative blood cultures were sterile. Cultures of the excised anterior mitral valve leaflet were negative for bacterial growth, likely due to the targeted antimicrobial therapy administered before surgery. Following a series of therapies, the patient was discharged with a three-week course of continuous intravenous meropenem therapy to complete the treatment regimen. The decision to shorten the treatment duration for C. koseri bacteremia from the usual six weeks for non-surgical IE was based on the removal of the infection source and the absence of any residual infection in the surrounding heart valve structures as observed during surgery. Three subsequent monthly follow-ups revealed persistently negative blood cultures, indicating the successful eradication of the infection. Discussion: Studies proposed shortening to 2 weeks for negative valve cultures revealed low incidence of relapse following surgical intervention, occurring only 0.8% of cases. Relapse, occurred in 2% of patients. No significant differences in relapse rates, 1-year recurrence, 1-year mortality, or postoperative complications between patients receiving antibiotics for more or less than two weeks. Conclusion: We report the successful management of a rare case of acute IE of the native mitral valve caused by C. koseri in an immunocompetent patient. Our treatment involved valve replacement and a shortened course of antimicrobial therapy.