Nocardiosis

Nocardiosis is a rare infection caused by Nocardia, a genus of aerobic, gram-positive bacteria. It manifests as either pulmonary, cutaneous, or disseminated disease. Pulmonary nocardiosis presents as a virulent form of pneumonia, which occurs more commonly in immunosuppressed individuals. As in any other type of pneumonia, productive cough, pleuritic chest pain, and fever are the dominant symptoms, making it difficult to differentiate from other lung infections. Cutaneous nocardiosis manifests with either cellulitis or purulent erythematous nodules. It may be accompanied by inflamed lymph nodes. The disseminated form predominantly occurs in immunocompromised patients and is typically associated with pulmonary or CNS involvement. A suspected diagnosis is confirmed via culture from infected material (e.g., sputum or skin samples). The mainstay of treatment is long-term antibiotic therapy with TMP/SMX. Without treatment, pulmonary nocardiosis and disseminated nocardiosis are usually fatal in immunocompromised patients.

• ♂ > ♀ (3:1) ^[1]
• Pulmonary infection is the most common ^[2]
• Systemic infection : the CNS is involved in up to 30% of cases ^[3]

Epidemiological data refers to the US, unless otherwise specified.

• Pathogen: Nocardia; species (ubiquitous in soil worldwide) ^[4]
  • N. otitidiscaviarum
  • N. brasiliensis
  • Nocardia asteroides complex
• Transmission: inhalation (most common), ingestion, and inoculation through a skin wound or injury
• Risk factors
  • Immunocompromise; (e.g., due to HIV infection, organ transplant, glucocorticoid therapy, recent chemotherapy, diabetes mellitus)
  • Advanced age

Pulmonary nocardiosis ^[5]

• Course: acute, subacute, or chronic
• Risk group: immunocompromised individuals
• Clinical features
  • Constitutional: fever, weight loss, anorexia, night sweats
  • Respiratory (recurrent pneumonia): productive cough, dyspnea, pleuritic chest pain
  • Pulmonary nocardiosis symptoms such as fever, chills, and weight loss are often mistaken for tuberculosis

Cutaneous nocardiosis

• Primary infection
  • Superficial cutaneous: cellulitis; (pain, swelling, erythema, and warmth), nodules, abscesses, ulceration
  • Lymphocutaneous: superficial cutaneous infection, regional lymphadenopathy, and lymphangitis
  • Subcutaneous mycetoma: chronic pyogenic lesion of the extremities (usually affecting the feet, back, and hands) → painless indurated nodule → draining sinus tract
• Cutaneous involvement
  • Originates from a disseminated focus or after trauma
  • Indiscernible from primary lesions, although features of underlying systemic disease (pneumonia, seizures, focal deficits) are present

Disseminated nocardiosis

• Definition: two or more sites of involvement
• Clinical features: generally involves both the lungs and the brain
  • Pulmonary findings are prominent.
  • Metastatic abscesses may be found almost anywhere but are predominantly located on the lower extremities.
  • CNS features: headache, lethargy, confusion, seizures, sudden onset of neurological deficits

The combination of pneumonia and abscess in the lower extremities is particularly suggestive of nocardiosis.

• Culture: confirmatory test
  • Specimens: sputum, skin biopsy samples, CSF fluid, and/or pus from the cutaneous lesions
  • Gram-positive aerobic bacilli, weakly acid-fast; , branching filamentous rods
• Imaging
  • Chest x-ray or CT
    • Pulmonary nodules (with or without cavitation)
    • Infiltrates (reticulonodular pattern or diffuse)
    • Abscess, empyema
  • Head CT or MRI: brain abscesses ^[5]

• Antibiotic therapy: trimethoprim-sulfamethoxazole (drug of choice)
  • Long-term therapy of at least 6 months is recommended.
  • Alternatives: carbapenems (imipenem or meropenem), third-generation cephalosporins (cefotaxime or ceftriaxone), and amikacin are indicated:
    • As part of combination therapy
    • In patients with an allergy or intolerance to sulfonamides
    • First-line treatment failure
• Interventional management
  • Surgical drainage of abscesses and debridement of necrotic tissue
  • Brain abscesses typically require stereotactic aspiration or surgical excision (See “Treatment of brain abscess”). ^[6]
  • Complications of pulmonary infection (e.g., empyema, mediastinal fluid collections, pericardial effusion) may require surgical intervention. ^[7]