1. Prepared by Laetitia Daou MD and reviewed by Patricia Simner PhD

Middle-aged adult with human immunodeficiency virus (HIV) (absolute CD4+ lymphocytes 284 /cu mm; viral load undetectable), end stage renal disease secondary to hypertension vs. HIV-associated nephropathy status post kidney transplant, and nonischemic cardiomyopathy (ejection fraction 60-65%), who presents to the emergency department with several weeks history of low-grade fever, night sweats, significant weight loss, fatigue, weakness, chest discomfort, shortness of breath decreased P.O. appetite & P.O. intolerance. Computed tomography (CT) scan of the chest is ordered as part of the workup to rule out post-transplant lymphoproliferative disorder and shows bilateral multiple 2-3 mm pulmonary nodules with faint ground glass opacities possibly related to infection, as well as multiple prominent upper abdominal, pericardial and subcarinal reactive lymph nodes and splenomegaly. Bone marrow biopsy is performed and returns negative for lymphoproliferative disorder, hemophagocytes or granulomas. Laboratory findings reveal pancytopenia, hyperferritinemia, hypertriglyceridemia and elevated liver enzymes. Microbiology studies are unremarkable. Endocarditis workup including culture and cardiac echocardiogram is negative. Tick-borne infectious workup is negative. Liver biopsy shows inflammatory infiltrates, granulomas and hemophagocytosis. Warthin-Starry stain performed on the liver granulomas reveals the following:



Figure 1: Clusters of short rods (arrows) shown on Warthin-Starry stain.

Which of the following is the most likely etiologic organism?