- Clinical science
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)
- Purely pulmonary involvement: ∼ 40% of cases
- Systemic infection: : ∼ 30% of cases (with the CNS being involved in about half of systemic cases)
Epidemiological data refers to the US, unless otherwise specified.
- Transmission: inhalation (most common), ingestion, and inoculation through a skin wound or injury
- Risk factors
- Onset: acute, subacute, or chronic
- Constitutional symptoms: fever, weight loss, anorexia, night sweats
- Respiratory symptoms (recurrent pneumonia): productive cough, dyspnea, pleuritic chest pain
- 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 from a disseminated focus
- Definition: two or more sites of involvement
- Generally involves both the lungs and the brain
The combination of pneumonia and abscess in the lower extremity is particularly suggestive of nocardiosis!
Culture (confirmatory test ): from sputum, skin biopsy samples, CSF fluid, or pus from the cutaneous lesions
- Gram-positive aerobic bacilli, weakly acid-fast; , branching filamentous rods
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:
Indications for surgery
- Surgical drainage of abscesses and debridement of necrotic tissue
- CNS abscesses: indicated if the lesions are easily accessible, not responsive to 2 weeks of antimicrobial therapy, or are large
- Complications of pulmonary infection (e.g., empyema, mediastinal fluid collections, pericardial effusion) may require surgical intervention.