Case Report: First report of Legionella micdadei pneumonia and organizing pneumonia in a patient with myelodysplastic and Sweet syndromes

The immunocompromised population is susceptible to <i>Legionella</i> pneumonia. The diagnosis and treatment of <i>Legionella</i> pneumonia in immunocompromised individuals are challenging clinical endeavors. Previous studies have identified <i>Legionella</i> pneumonia as a potential cause of organizing pneumonia (OP), however, the association between <i>Legionella</i> pneumonia and OP has not received enough clinical attention. We retrospectively evaluated a case involving <i>Legionella micdadei</i> infection and OP in a patient with myelodysplastic syndrome and concurrent Sweet syndrome. The diagnosis of <i>Legionella micdadei</i> pneumonia was confirmed through various methods: metagenomic next generation sequencing (mNGS), Giemsa-staining and fluorescence <i>in situ</i> hybridization of lung tissue, as well as serum immunofluorescence antibody testing. Histopathological analysis of lung tissue revealed OP. The patient was successfully treated with a combination of antibiotics and low-dose glucocorticoids. In immunocompromised individuals, mNGS was capable of detection non-<i>Legionella</i> pneumophila serogroup 1. The pathological examination is important for identifying secondary OP and provides the evidence for treatment with glucocorticoids.