Legionella maceachernii Pneumonia Presenting as a Cavitary Lesion in an Immunocompromised Patient.

Legionella is an intracellular, gram-negative bacterium known as a less common cause of pneumonia, which has become a public health concern in recent years due to increased incidence. Legionella pneumophila is recognized as the most common cause of Legionnaires' disease. Other Legionella species, including Legionella maceachernii, have been rarely described as causes of Legionnaires' disease. Moreover, cavitary lesions as radiological findings in patients with Legionnaires' disease are uncommon but have been reported, especially in immunocompromised patients. Although the gold standard for diagnosis is a positive culture, the need for special media and extended time for growth can overlook or delay diagnosis. Additionally, urine antigen testing will miss detection of species other than Legionella pneumophila serogroup 1. Molecular testing, although not routinely performed, is a promising tool for early detection and identification of other Legionella species. We present a case of an immunocompromised patient presenting with fevers and a cavitary lesion, diagnosed with Legionella maceachernii through cell-free DNA sequencing.