Nocardia species are aerobic filamentous soil bacteria that can cause pulmonary and systemic nocardiosis. Common Nocardia species include members of the Nocardia asteroides complex and Nocardia brasiliensis. Bronchopulmonary abnormalities (eg, alveolar proteinosis) predispose to colonization, but infection is unusual unless the patient is also receiving systemic corticosteroids or is otherwise immunosuppressed.
Pulmonary involvement usually begins with malaise, loss of weight, fever, and night sweats. Cough and production of purulent sputum are the chief complaints. Radiography may show infiltrates accompanied by pleural effusion. The lesions may penetrate to the exterior through the chest wall, invading the ribs.
Dissemination involves any organ. Brain abscesses and subcutaneous nodules are most frequent. Even in the absence of clinical symptoms and signs of CNS infection, clinicians should consider brain imaging in patients with nocardiosis to rule out an occult abscess.
Nocardia species are usually found as delicate, branching, gram-positive filaments. They may be weakly acid-fast, occasionally causing diagnostic confusion with tuberculosis. Identification is made by culture.
For isolated cutaneous infections, therapy is initiated with trimethoprim-sulfamethoxazole administered at a dosage of 5–10 mg/kg/day (based on trimethoprim) as an oral or intravenous formulation. Surgical procedures such as drainage and resection may be needed as adjunctive therapy. A higher dose of 15 mg/kg/day (based on trimethoprim) should be used for disseminated or pulmonary infections. Resistance to trimethoprim-sulfamethoxazole is increasing and initiating treatment with two drugs while awaiting antibiotic susceptibilities in cases of disseminated or severe localized disease should be considered. Alternative agents or drugs that can be given in combination with trimethoprim-sulfamethoxazole include imipenem, 500 mg intravenously every 6 hours; amikacin, 7.5 mg/kg intravenously every 12 hours; or minocycline, 100–200 mg orally or intravenously twice daily. Consultation with an infectious diseases expert is encouraged.
Response may be slow, and therapy should be continued for at least 6 months. The prognosis in systemic nocardiosis is poor when diagnosis and therapy are delayed.
M. Nocardiosis from 1888 to 2017. Microb Pathog. 2018 Jan;114:369–84.
et al. Pulmonary nocardiosis: a clinical analysis of 30 cases. Intern Med. 2017;56(12):1485–90.