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

Abstract

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.

Legionella micdadei: A Forgotten Etiology of Growing Cavitary Nodules: A Case Report and Literature Review

“…Pulmonary nodules are common in immunocompromised patients and account for significant morbidity and mortality [ 5 ]. The nodule etiology varies by degree of immunosuppression, prophylaxis, exposures, and medical history [ 6 ] making them difficult for diagnosis [ 3 ]. The infectious differential includes invasive fungal diseases which are the most common cause (e.g., Aspergillus , Cryptococcus , and Zygomycetes), Nocardia , Legionella , mycobacterial infection, viral (e.g., CMV, adenovirus), septic emboli, or endocarditis.…”

“…The infectious differential includes invasive fungal diseases which are the most common cause (e.g., Aspergillus , Cryptococcus , and Zygomycetes), Nocardia , Legionella , mycobacterial infection, viral (e.g., CMV, adenovirus), septic emboli, or endocarditis. [ 6 ]. Once infiltrates are identified on radiograph fiberoptic bronchoscopy with lavage and possible transbronchial biopsy should be undertaken early and when safe to improve identification of the causative organism to help ensure proper and narrow antimicrobial coverage [ 5 ].…”

Emerging respiratory infections: The infectious disease pathology of SARS, MERS, pandemic influenza, and Legionella

“…2D), which can lead to diagnostic mis-adventures. 81,82 In addition to Mycobacteria and several parasites, a handful of Gram-positive organisms including Nocardia, Rhodococcus, Tsukamurella, Gordonia, and Dietzia can also stain by modified acid-fast stains. In contrast to L. micdadei, all of these organisms should stain Gram positive.…”

Pneumonia and pulmonary abscess due to Legionella micdadei in an immunocompromised patient

“…L. micdadei are ubiquitous bacteria responsible for pneumonias that preferentially affect profoundly immunosuppressed people, as was our patient under immunosuppressive medications and more recently added high-dose corticosteroids. 1,2,[4][5][6][7] The reasons why L. micdadei are rarely found in healthy people are not clear. Even if L. micdadei and L. pneumophila share virulence genes, it seems that L. micdadei are less virulent than L. pneumophila, and show fewer cytotoxic capacities when cultured with macrophages.…”

“…3 Rare cases of endocarditis, brain abscess, cellulitis, or prosthetic joint infections due to L. micdadei have been published, but it has a predilection for causing pneumonia in immunocompromised hosts. 1,2,[4][5][6][7] The mortality rate of L. micdadei infections may be around 20% in some series. 2 We report a case of L. micdadei pneumonia and discuss the difficulties encountered in establishing the diagnosis.…”