Pathological investigation and microbiological confirmation of Bartonella quintana endocarditis: A case of trench fever without the trench or fever

<i>Bartonella quintana</i> is a louse-borne Gram-negative bacterium first discovered as the cause of trench fever during World War I. As <i>B. quintana</i> is not identified using routine culture with 5-day incubation, the pathogen is an agent of blood culture-negative endocarditis, particularly among individuals experiencing homelessness. Here, we describe a case of an 80-year-old man who presented in the winter of 2017 with severe aortic valve regurgitation resulting in exercise intolerance, requiring aortic valve replacement. Pathological assessment of the explanted aortic valve revealed changes of infective endocarditis. The presence of <i>B. quintana</i> in the valve tissue was confirmed using molecular methods including <i>B. quintana</i>-specific polymerase chain reaction (PCR) as well as PCR and sequencing of the 16S rRNA, heat shock protein (<i>hsp</i>), and RNA polymerase (<i>rpoB</i>) genes. The organism was subsequently grown from the patient's blood. Serology revealed <i>B. quintana</i> IgG titres that were initially elevated at 1:4096, but decreased and were sustained at 1:1024, as the patient recovered following treatment with doxycycline and rifampin. <i>Bartonella quintana</i> endocarditis is recognized as a cause of culture-negative endocarditis, but the diagnosis can be difficult, as symptoms may be non-specific, and the organism requires special conditions (and media) for routine growth. This case emphasizes the value of pathological investigations and microbiology laboratory support in the setting of low clinical and intraoperative suspicion of infective endocarditis.