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 an aerobic, facultative, intracellular gram - rod transmission aspiration of contaminated water/soil air conditioning hot tubs swimming pools Associated conditions Legionnaires disease (most common) lobar or insterstitial pneumonia gastrointestinal and central nervous system involvement more common in smokers and those with chronic lung diseases 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 confusion encephalopathy Physical exam fever altered mental status dyspnea relative bradycardia pneumonia Imaging Chest radiography indication all patients findings lobar consolidation or diffuse patchy infiltrates Studies Labs urine antigen test diagnostic does not Gram stain well, so this requires a silver stain sputum culture requires special media for culture charcoal yeast extract agar buffered with iron and cysteine hyponatremia transaminitis Making the diagnosis based on clinical presentation and laboratory studies Differential Mycoplasma pneumoniae distinguishing factor typically does not present with gastrointestinal or central nervous system involvement Treatment Medical antibiotics indication all patients drugs macrolides respiratory fluoroquinolones (levofloxacin and moxifloxacin) Complications Respiratory failure