Mistaken identity: Legionella micdadei appearing as acid fast bacilli on lung biopsy of a hematopoietic stem cell transplant patient

摘要

Legionella micdadei is a potential cause of invasive lung infections in immunocompromised hosts. On biopsy specimens, it can appear as an acid-fast bacillus (AFB) and can be mistaken for a member of genus Mycobacterium. As Legionella requires selective media to grow in culture, and a commonly used, commercially available urine antigen test for Legionella only detects Legionella pneumophila serogroup 1 but not L. micdadei, it is important to consider this organism in the differential diagnosis for AFB in immunocompromised hosts. We report a case of Legionella micdadei infection, which was initially treated empirically for non-tuberculous mycobacteria based on acid fast staining of biopsy tissue before the final diagnosis was made.