Nocardiosis

Key Features

• Nocardia species are an aerobic filamentous soil bacterium that can cause pulmonary and systemic nocardiosis

• Commonly identified 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

• Central nervous system (CNS) involvement commonly accompanies pulmonary infection

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 from pneumonia may involve any organ, especially CNS, skin, and bone, or there may be primary cutaneous disease

  • Brain abscesses and subcutaneous nodules are most frequent

  • Cutaneous lesions may mimic actinomycosis

  • Dissemination is seen exclusively in immunocompromised patients

Diagnosis

• Suspect in setting of chronic lung disease or immunocompromised host

• N asteroides is a branching, filamentous gram-positive bacterium that is weakly acid-fast

• Identification is made by culture

• Chest radiograph

  • May show infiltrates accompanied by pleural effusion

  • Lesions may penetrate through the chest wall and invade the ribs

• Brain imaging should be considered even in absence of clinical symptoms and signs of CNS infection to rule out occult abscess

Treatment

• Trimethoprim-sulfamethoxazole (TMP-SMZ)

  • For isolated primary cutaneous infections

    • 5–10 mg/kg/day (based on TMP) as an oral or intravenous formulation

  • For disseminated or pulmonary infections: 15 mg/kg/day (based on TMP)

  • Resistance to TMP-SMZ is increasing and initiating treatment with two drugs should be considered while awaiting antibiotic susceptibilities in cases of disseminated or severe localized disease

• Alternative agents or drugs that can be given in combination with TMP-SMZ

  • Imipenem, 500 mg intravenously every 6 hours

  • Amikacin, 7.5 mg/kg intravenously every 12 hours

  • Minocycline, 100–200 mg orally or intravenously twice daily

• Surgical procedures such as drainage and resection may be needed as adjunctive therapy for isolated cutaneous disease

• Response may be slow, and therapy should be continued for at least 6 mo

• The prognosis in systemic nocardiosis is poor when therapy is delayed