A 46-year-old man comes to the emergency department due to a week of fever, chills, productive cough with yellow-white sputum, and shortness of breath. The patient received an allogenic renal transplantation 6 months ago and currently takes maintenance immunosuppressive therapy. He is a former smoker and works in a post office. Temperature is 39.4 C (102.9 F), blood pressure is 110/65 mm Hg, pulse is 110/min, and respirations are 22/min. Lung auscultation reveals left upper lung crackles and bronchial breath sounds. Chest imaging reveals a left upper lobe nodular density with cavitation and nodular infiltrates in the right lung. Sputum Gram stain and culture are negative. Bronchoalveolar lavage cultures yield light growth of branching, filamentous rods that are partially acid-fast, as shown in the image below. Which of the following is the most likely causative organism of this patient's condition?

Question

A 46-year-old man comes to the emergency department due to a week of fever, chills, productive cough with yellow-white sputum, and shortness of breath.  The patient received an allogenic renal transplantation 6 months ago and currently takes maintenance immunosuppressive therapy.  He is a former smoker and works in a post office.  Temperature is 39.4 C (102.9 F), blood pressure is 110/65 mm Hg, pulse is 110/min, and respirations are 22/min.  Lung auscultation reveals left upper lung crackles and bronchial breath sounds.  Chest imaging reveals a left upper lobe nodular density with cavitation and nodular infiltrates in the right lung.  Sputum Gram stain and culture are negative.  Bronchoalveolar lavage cultures yield light growth of branching, filamentous rods that are partially acid-fast, as shown in the image below.  Which of the following is the most likely causative organism of this patient's condition?

Quizplus · Accepted Answer

11ec25c8_d464_9130_bc81_4bd90a4ff9f5_MD0003_00 Nocardia is an aerobic bacteria found in soil that may inoculate humans via inhalation (most common) or cutaneous penetration (often while gardening). Branching, filamentous growth helps the organism prevent phagocytosis, making host defense largely dependent on cell-mediated immunity. Therefore, patients who are severely immunocompromised (eg, immunosuppressive medications, HIV) are much more likely to develop active disease. Pulmonary nocardiosis is the most common manifestation and may present alone or with disseminated disease (eg, skin, central nervous system). Symptoms arise with varying chronicity but often include fever, weight loss, malaise, dyspnea, cough, and pleurisy. Imaging typically reveals nodular or cavitary lesions in the upper lobes, which may be confused with malignancy or tuberculosis. Sputum culture is often negative, but bronchoscopy with bronchoalveolar lavage can usually provide an adequate sample for diagnosis (sensitivity >85%). Gram stain shows filamentous gram-positive rods that are weakly acid-fast (unlike Mycobacterium tuberculosis [Choice E], which is strongly acid-fast). Cultures often require >4 weeks of incubation. Susceptibility testing is needed for all isolates as many strains are antibiotic resistant. Trimethoprim-sulfamethoxazole is usually the treatment of choice and may be combined with additional antibiotics (eg, amikacin) in severe disease. Several months of antibiotics are usually required, and relapse is common despite adequate treatment. (Choice A) Actinomyces typically causes cervicofacial disease (nonpainful, chronic, mandibular mass) and is anaerobic/acid-fast negative (unlike Nocardia). (Choice B) Aspergillus may cause pulmonary disease (upper lobe cavitary disease) in immunocompromised patients, but microscopy would show acid-fast negative hyphae (not filamentous, weakly acid-fast rods). Aspergillus (Choice C) Bacillus anthracis is a sporulating (not branching, filamentous) bacterium that can be inhaled. Symptoms progress rapidly and include fever, myalgias, dyspnea, hypoxemia, and shock. (Choice D) Klebsiella pneumoniae is a gram-negative, acid-fast negative rod that may cause nosocomial infections, including hospital-acquired pneumonia. (Choices G and H) Peptostreptococcus and Streptococcus pyogenes may cause skin infections. Both organisms are acid-fast negative. Educational objective: Nocardia most commonly causes pulmonary disease in an immunocompromised host, with or without extrapulmonary manifestations (eg, skin, central nervous system). Nocardiosis is diagnosed by culture and the presence of filamentous, gram-positive, weakly acid-fast rods on Gram stain. Trimethoprim-sulfamethoxazole is the treatment of choice. References: Current treatment for nocardia infections. (http://www.ncbi.nlm.nih.gov/pubmed/24093436) Nocardiosis: updates and clinical overview. (http://www.ncbi.nlm.nih.gov/pubmed/22469352) Nocardia infections in solid organ transplantation. (http://www.ncbi.nlm.nih.gov/pubmed/23465002)

A 46-Year-Old Man Comes to the Emergency Department Due to a Week