Subacute Bartonella endocarditis with glomerulonephritis: a diagnostic and therapeutic challenge in blood culture–negative infective endocarditis

<b>Background.</b> <i>Bartonella</i> species are increasingly recognized as a significant cause of blood culture-negative infective endocarditis. Their diagnosis is often challenging, leading to delays and suboptimal treatment outcomes. <b>Case report.</b> This report includes a concise literature review and a case involving a 77-year-old male with a history of bovine aortic valve replacement. The patient presented with lethargy, fever, unintentional weight loss and acute kidney injury. Despite repeated blood cultures and extensive diagnostic evaluations yielding negative results, the definitive diagnosis was achieved post-surgery when valve PCR identified <i>Bartonella</i> species, likely linked to cat exposure. The patient was successfully treated with an extended course of doxycycline and rifampicin, leading to clinical resolution. <b>Conclusion.</b> This case highlights the diagnostic complexities of <i>Bartonella</i> endocarditis, including negative blood cultures, subacute clinical presentation and its ability to mimic autoimmune glomerulonephritis, leading to unnecessary immunosuppressive therapy. It underscores the need for improved diagnostic approaches and clinician awareness to identify at-risk populations, such as those with cat exposure or poor hygiene, ensuring the correct diagnostic investigation for an early antibiotic intervention.