33-33: Nocardiosis

ESSENTIALS OF DIAGNOSIS

GENERAL CONSIDERATIONS

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, bronchiectasis) predispose to colonization, but infection is unusual unless the patient is also receiving systemic corticosteroids or is otherwise immunosuppressed.

CLINICAL FINDINGS

Pulmonary involvement usually begins with malaise, loss of weight, fever, and night sweats. Cough and production of purulent sputum are the chief complaints. Pulmonary infiltrates may penetrate to the exterior through the chest wall, invading the ribs.

Dissemination involves any organ. Brain abscesses and subcutaneous nodules are most frequent. Cutaneous lesions may mimic actinomycosis. Radiography may show infiltrates accompanied by pleural effusion. 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.

TREATMENT

For isolated primary cutaneous infections, therapy is initiated with trimethoprim-sulfamethoxazole orally or intravenously (5–10 mg/kg/day based on trimethoprim). Surgical procedures such as drainage and resection may be needed as adjunctive therapy for isolated cutaneous disease. A higher dose of 15 mg/kg/day (based on trimethoprim) should be used for disseminated or pulmonary infections. Resistance to trimethoprim-sulfamethoxazole has increased and initiating treatment with two drugs while awaiting antibiotic susceptibilities in cases of disseminated or severe localized disease should be considered. Brain abscesses or pneumonia should be initially treated with combination therapy. 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 disease expert is encouraged.

Response may be slow; therapy should be continued for at least 6 months. The prognosis in systemic nocardiosis is poor when diagnosis and therapy are delayed.