Bartonella quintana endocarditis presenting with severe coombs-positive anemia: a case report

Bartonella quintana is a recognized cause of blood culture-negative endocarditis, often associated with predisposing social factors or pre-existing valvulopathy. Diagnosis is challenging and relies on advanced microbiological techniques. A 17-year-old Tibetan herdsman from a high-altitude region presented with a two-week history of fever, dyspnea, and lower limb edema. He had no history of homelessness or alcoholism but lived in poor sanitary conditions. Laboratory investigations revealed severe Coombs-positive hemolytic anemia and serological markers suggestive of systemic lupus erythematosus (SLE). Transthoracic echocardiography showed vegetations on both aortic (bicuspid) and mitral valves with severe regurgitation and rapid hemodynamic progression. All blood cultures were negative. Metagenomics Next-Generation Sequencing (mNGS) of peripheral blood identified B. quintana as the causative pathogen. Antibiotic therapy was adjusted to doxycycline (9 weeks) and gentamicin (3 weeks). Concurrently, immunomodulatory therapy with methylprednisolone and intravenous immunoglobulin was administered for the hemolytic anemia. Given the severe valvular insufficiency, the patient successfully underwent urgent aortic and mitral valve replacement. His clinical condition improved significantly post-operatively. This case highlights the diagnostic utility of mNGS in confirming B. quintana endocarditis in a culture-negative scenario, especially when clinical presentation is complicated by concomitant autoimmune features mimicking Libman-Sacks endocarditis. A treatment strategy combining targeted antibiotics for the infection and immunomodulation for the hematologic complication, followed by definitive surgery, led to a successful outcome. It underscores that B. quintana infection should be considered in patients from disadvantaged backgrounds with endocarditis, even in the absence of classic risk factors.