A 58-year-old man comes to the emergency department with 3 days of fever, malaise, nonproductive cough, abdominal pain, diarrhea, and shortness of breath. He has a past medical history of hypertension, hypothyroidism, and coronary artery disease. The patient travels frequently within the United States and just returned from a week-long business conference. Yesterday, his abdominal pain worsened and he began to have diarrhea. His temperature is 38.9 C (102 F), blood pressure is 98/59 mm Hg, pulse is 75/min, and respirations are 29/min. The patient's pulse oximetry shows 94% on room air. He appears confused. Examination shows diffuse crackles over the left lung field. Chest x-ray reveals patchy infiltrates in the left lung without adenopathy. A sputum sample is obtained for smear and culture; the Gram stain shows many neutrophils but no organisms. Laboratory results are as follows: Which of the following tests is most likely to identify the cause of this patient's condition?

Question

A 58-year-old man comes to the emergency department with 3 days of fever, malaise, nonproductive cough, abdominal pain, diarrhea, and shortness of breath.  He has a past medical history of hypertension, hypothyroidism, and coronary artery disease.  The patient travels frequently within the United States and just returned from a week-long business conference.  Yesterday, his abdominal pain worsened and he began to have diarrhea.  His temperature is 38.9 C (102 F), blood pressure is 98/59 mm Hg, pulse is 75/min, and respirations are 29/min.  The patient's pulse oximetry shows 94% on room air.  He appears confused.  Examination shows diffuse crackles over the left lung field.  Chest x-ray reveals patchy infiltrates in the left lung without adenopathy.  A sputum sample is obtained for smear and culture; the Gram stain shows many neutrophils but no organisms.  Laboratory results are as follows:  Which of the following tests is most likely to identify the cause of this patient's condition?

Quizplus · Accepted Answer

11ec25c8_d45c_7ad4_bc81_f3c0b15fd101_MD0003_00 This patient most likely has Legionnaires' disease, given his presentation suggestive of an atypical community-acquired pneumonia with central nervous system (confusion) and gastrointestinal (abdominal pain, diarrhea, hepatitis) features. The primary environmental source of Legionella pneumophila is water, where it lives inside of protozoa. It is transmitted to humans by droplets or aerosols, often through air-conditioning systems and showers. Hotels and cruise ships are frequently implicated in outbreaks; this patient's recent business trip may have resulted in exposure. Nosocomial outbreaks can occur when the hospital's potable water supply or respiratory equipment becomes colonized. In Legionnaires' disease, pulmonary manifestations are often accompanied by other organ dysfunction, ranging from central nervous system and gastrointestinal involvement to fulminant disease with multi-organ failure. Relative bradycardia (despite high fever) is a classic association; hyponatremia and mild hepatitis, as in this patient, are frequently seen. Legionella is an intracellular gram-negative rod, so sputum Gram stain may show neutrophils but no organisms. The diagnosis can be made by culture, generally from bronchoscopy. However, Legionella is difficult to recover even when selective media (buffered charcoal yeast extract) are used. Urine antigen testing is rapidly available, highly specific, and the most common method to confirm the diagnosis. When Legionnaires' disease is suspected or proven, therapy should include a macrolide or fluoroquinolone. (Choice A) Influenza is a common cause of community-acquired pneumonia, particularly in the winter. However, gastrointestinal or central nervous system manifestations are rare in influenza. Unilateral lung findings would also be unusual. (Choice B) Mycoplasma pneumonia is more likely in children or young adults, and the constellation of hyponatremia and gastrointestinal symptoms is more suggestive of Legionella infection in this patient. Extrapulmonary manifestations are less commonly seen in Mycoplasma pneumonia. (Choice C) Pneumocystis pneumonia occurs in patients with severely impaired T-cell immunity, most commonly those with AIDS or transplant recipients. It generally presents subacutely, with bilateral radiographic findings and sometimes profound hypoxia. None of these features are seen in this patient. (Choice D) Acute presentations of tuberculosis (TB) are relatively uncommon. Disseminated TB can present with multi-organ involvement in the setting of primary infection (miliary TB) or reactivation disease (apical infiltrates). However, this patient has no prominent risk factors for TB, is not immunocompromised, and does not have x-ray findings consistent with either miliary or reactivation TB. Educational objective: Legionnaires' disease can present similarly to other atypical community-acquired pneumonias. However, concurrent gastrointestinal and central nervous system symptoms may suggest Legionnaires'. Diagnosis can be confirmed with urine antigen testing in combination with culture. References: Epidemiology and clinical management of Legionnaires' disease. (http://www.ncbi.nlm.nih.gov/pubmed/24970283) Systematic review and metaanalysis: urinary antigen tests for Legionellosis. (http://www.ncbi.nlm.nih.gov/pubmed/19318671) Legionella infections and travel associated legionellosis. (http://www.ncbi.nlm.nih.gov/pubmed/21995862)

A 58-Year-Old Man Comes to the Emergency Department with 3