Cases

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Primary pulmonary nocardiosis: Cultures of the BAL fluid and the specimen obtained during CT-guided needle aspiration grew Nocardia asteroides. Bacteria of the genus Nocardia are among the group of ubiquitous microorganisms known as the aerobic actinomycetes. The bacteria are found worldwide in the environment, in the soil, and in vegetable matter. The organism is a filamentous gram-positive, partially acid-fast rod with delicate branching hyphae. Inhalation of the sporulated mycelial fragments may lead to lung infection. In North America, the predominant species that infects humans is N asteroides. Men are infected 3 times more frequently than women, and approximately 500-1000 cases occur in the United States per year. Person-to-person transmission of Nocardia is not thought to occur. Mechanisms of the normal host defense against Nocardia are not fully understood, but resistance clearly requires sufficient numbers of functioning phagocytes and polymorphonuclear cells as well as an intact cell-mediated immunity. As many as 85% of infected individuals have altered immune responses. Other predisposing factors are corticosteroid treatment for chronic obstructive lung disease, solid-organ transplantation, diabetes mellitus, hematologic or solid malignancies, alcoholism and/or cirrhosis, renal failure, lupus, and AIDS. Because the portal of entry is most commonly the respiratory tract, most patients with clinically recognized nocardial infections present with pulmonary signs and symptoms. The pulmonary presentation may be acute, but it is most often chronic and insidious. The most common symptom is purulent sputum production. Because most infected patients are immunocompromised, the tendency of nocardial pulmonary infections to disseminate to other organs via hematogenous routes is not surprising. In most recent studies, disseminated extrapulmonary infection occurred in 10-50% of patients. Metastatic infection has been documented in nearly every organ, but the typical sites of involvement are the CNS (brain, meninges, spinal cord), skin, subcutaneous tissues, kidneys, joints, bones, heart, and eyes. On plain radiography and CT, usual presentations of nocardial lung infection are nonsegmental air-space consolidation in a reticulonodular pattern and the formation of pulmonary nodules. Of note, solitary pulmonary nodules are more frequent than multiple nodules. Other radiographic presentations are large and small cavitary lesions and miliary patterns. Pleural effusion and empyema occur in 25% of patients. Hilar involvement and calcification are rare. Evaluation of appropriate specimens by performing smears and cultures is the primary method of diagnosis. Gram staining of respiratory secretions is sensitive and sufficient for identifying Nocardia organisms in 65-80% of patients, but the results should always be confirmed with cultures. Nocardia species usually grow easily on most routine bacteriologic media and typically appear in 2-7 days. In some cases, however, the nocardial strain is slow growing and may not appear for 2-3 weeks. The standard practice of clinical microbiology laboratories is to discard routine cultures of respiratory specimens after 5 days of incubation. If the clinician suspects nocardial infection, the laboratory staff should be alerted to observe the culture for an extended period. Blood cultures are positive in a minority of patients but should be obtained when pulmonary or disseminated disease is suspected. When the disease is disseminated, the diagnosis is usually made by sampling the affected end organ. At present, no serologic technique or molecular technique is available for routine clinical use. About 90% of pulmonary infections due to N asteroides respond favorably to sulfonamides. Sulfadiazine is preferred for infections of the CNS because of its penetration into the spinal fluid, but the combination of sulfamethoxazole (SMZ) with trimethoprim (TMP) is considered an acceptable alternative. For patients unable to take sulfonamides, parenteral therapies are carbapenems (imipenem and cilastatin or meropenem), third-generation cephalosporins (cefotaxime or ceftriaxone), and amikacin alone or in combination. Alternative oral therapies include minocycline and amoxicillin with clavulanate. For most cases of pulmonary nocardiosis, antibiotics should be continued for a minimum of 6 months. Patients receiving immunosuppressive therapy can generally continue with that therapy while being treated for the nocardial infection. In immunocompromised patients without HIV infection, treatment is continued for 12 months. In patients with AIDS, secondary treatment after 12 months is usually maintained with low doses of TMP-SMZ. Surgical drainage is recommended as an adjunct to antibiotics whenever feasible. Indications for aspiration, drainage, or excision of nocardial abscesses are the same as those for other bacterial infections. The mortality rate associated with pulmonary nocardial infection was once 80%. Patients' prognoses have improved with advancements in antibiotics and imaging techniques. Today, 90% of patients with nondisseminated pleural pulmonary disease survive. For more information on nocardiosis, see the eMedicine articles Nocardiosis and Solitary Pulmonary Nodule (within the Internal Medicine specialty), Nocardiosis (within the Dermatology specialty), and Nocardiosis (within the Pediatrics specialty).