Snapshot A 75-year-old woman returns from a week-long cruise with a cough and sputum production. Her family notices that she seems more confused than usual and brings her into the hospital. Earlier today, she had complained of nausea and vomiting. On physical exam, her pulse is 60/min. There are fine crackles diffusely on chest auscultation. Laboratory tests show that she has hyponatremia and mildly elevated transaminitis. A urine antigen test is positive for the suspected disease and she is started on antibiotics. Introduction Classification Legionella pneumophila login to view 1 more bullet transmission login to view 4 more bullets Associated conditions Legionnaires disease (most common) login to view 3 more bullets Epidemiology Demographics more common in the elderly Risk factors cruise ships smoking immunosuppression hospitalization ETIOLOGY Pathogenesis organism is phagocytosed into alveolar macrophages, where they replicate bacterial spread occurs when they escape from macrophage vacuoles leading to host cell osmotic lysis Presentation Symptoms cough with sputum production gastrointestinal symptoms nausea or vomiting water diarrhea central nervous system symptoms login to view 2 more bullets Physical exam fever altered mental status dyspnea relative bradycardia pneumonia Imaging Chest radiography indication login to view 1 more bullet findings login to view 2 more bullets Studies Labs urine antigen test login to view 1 more bullet does not Gram stain well, so this requires a silver stain sputum culture login to view 2 more bullets hyponatremia transaminitis Making the diagnosis based on clinical presentation and laboratory studies Differential Mycoplasma pneumoniae distinguishing factor login to view 1 more bullet Treatment Medical antibiotics login to view 5 more bullets Complications Respiratory failure