Nocardiosis
Nocardiosis is an opportunistic infection caused by aerobic, weakly acid-fast, branching gram-positive Nocardia species acquired from soil by inhalation or direct inoculation, most often producing necrotizing pulmonary disease with a strong tendency to hematogenously seed the brain, diagnosed by modified acid-fast stain and prolonged culture, and treated with high-dose trimethoprim-sulfamethoxazole, escalated with amikacin and imipenem for disseminated or CNS disease.
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What this article covers
- Overview
Opportunistic infection by an environmental, soil-dwelling organism: nocardiosis is caused by Nocardia species, aerobic, gram-positive, branching, filamentous bacteria that are weakly (modified)…
- Epidemiology
Nocardia is a saprophytic organism present in soil, dust, plants, and water worldwide, so exposure is common but clinical disease is concentrated in hosts with impaired cell-mediated immunity.
- Risk factors
HIV infection or AIDS, a recognized predisposing state for invasive nocardiosis.
- Pathophysiology
Inhalation of the organism from environmental soil, dust, or water delivers Nocardia to the lower respiratory tract, where impaired cell-mediated immunity permits establishment of infection rather than clearance.
- Clinical features
Pulmonary disease (most common): cough, dyspnea, chest pain, night sweats, fever, and weight loss, with imaging showing consolidation, cavitary lesions, or nodules that can be mistaken for malignancy.
- Differential diagnosis
Actinomycosis: another chronic, branching, filamentous gram-positive infection with mass-forming, sinus-tract-forming disease, but Actinomyces is anaerobic and not acid-fast (versus Nocardia's…
- Diagnosis
Nocardiosis is a microbiologic diagnosis confirmed by identifying branching, gram-positive, weakly (modified) acid-fast filaments on stain from an appropriate specimen, combined with growth on…
- Management
First, obtain source-directed drainage of any accessible abscess (pulmonary, subcutaneous, or CNS collection amenable to aspiration or surgical drainage) alongside starting antimicrobial therapy…
- Complications
Brain abscess from hematogenous CNS spread, the most serious complication, occurring in roughly 20% of affected patients and carrying the risk of focal neurologic deficit, seizure, and death if not identified and treated promptly.
- Prognosis
Outcome depends heavily on the extent of disease at diagnosis and the host's underlying immune status, with disseminated (particularly CNS) disease carrying a substantially worse prognosis than localized pulmonary or cutaneous disease.
- Prevention
No vaccine or chemoprophylaxis exists for nocardiosis; prevention centers on reducing exposure and modifiable immunosuppression risk.
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