Conditions · Infectious and tropical diseases
Nocardiosis !
Nocardiosis is an infection by soil bacteria that mainly affects people with weak immunity, causing lung infection and sometimes brain abscesses.
Updated 2026-11-01
Structures involved
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Microorganisms that cause it
Why it happens
- Outcomes of acute inflammation: resolution, abscess, scar or chronic inflammation
- White blood cells: types and functions
What it is
An infection by aerobic Nocardia species that live in soil and decaying plants. It usually starts in the lungs after inhalation, can spread through the blood, with the brain as the preferred site, and less often begins in the skin after a wound.
Who gets it
Nocardia is found worldwide. Most pulmonary and disseminated cases occur in people with impaired cell-mediated immunity, such as transplant recipients, people on long-term corticosteroids and people with advanced HIV. Men are affected about three times as often as women. In Colombia and other tropical countries Nocardia, especially N. brasiliensis, is also a cause of actinomycetoma of the feet (see mycetoma).
Causes
- Nocardia species (N. farcinica, N. nova, N. cyriacigeorgica, N. brasiliensis and others)
- Gram-positive, branching, beaded filaments that are weakly acid-fast
- Inhalation of soil dust (lung disease) or soil entering a wound (skin disease)
- Not spread from person to person
Risk factors
- Solid organ or bone marrow transplant
- Long-term high-dose corticosteroids or other immunosuppressive therapy
- Advanced HIV infection
- Cancer, diabetes and alcohol use disorder
- Chronic lung disease, including pulmonary alveolar proteinosis
Pathophysiology
Nocardia resists killing inside neutrophils and macrophages. In the lung it causes a suppurative, necrotising pneumonia that forms nodules, abscesses and cavities. When T-cell immunity is weak the organism enters the blood and seeds the brain, where it forms single or multiple, often multiloculated abscesses that grow slowly and may cause few symptoms at first.
Classification
- Pulmonary (most common)
- Disseminated, most often to the brain
- Primary cutaneous: cellulitis, lymphocutaneous or actinomycetoma
Symptoms and signs
- Subacute or chronic fever, cough, sputum, chest pain and weight loss
- Haemoptysis in cavitary disease
- Headache, seizures, focal weakness or personality change from brain abscesses
- Skin nodules or abscesses after a soil-contaminated wound
Diagnosis
- Clinical
- Considered in an immunosuppressed patient with a subacute pneumonia, nodules or cavities, especially together with a brain or skin lesion. Every patient with pulmonary disease needs brain imaging even without neurological symptoms.
- Tests
- Gram stain showing branching beaded filaments and modified acid-fast stain of sputum, bronchoalveolar lavage, pus or biopsy; culture, which may take several days (the laboratory should be told); molecular species identification and susceptibility testing, because resistance varies by species.
- Imaging
- Chest CT: nodules, masses, cavities, consolidation or empyema. Brain MRI or contrast CT: ring-enhancing, often multiloculated abscesses.
Differential diagnosis
- Tuberculosis and nontuberculous mycobacterial infection
- Invasive fungal infection (aspergillosis, cryptococcosis)
- Lung cancer and brain metastases
- Actinomycosis (anaerobic, not acid-fast)
- Bacterial lung abscess and toxoplasmosis (brain lesions in HIV)
Goal of treatment
Eradicate the infection with a long antibiotic course guided by species and susceptibility, drain large or unresponsive abscesses and, when possible, reduce immunosuppression to prevent relapse.
Treatment
- Medical
- A sulfonamide (trimethoprim-sulfamethoxazole) is the backbone of therapy; severe, brain or disseminated disease starts with a combination that may add amikacin, a carbapenem (imipenem) or a third-generation cephalosporin (ceftriaxone).
- Medical
- Prolonged treatment for months (often up to a year in brain or immunosuppressed disease) to prevent relapse, with review of immunosuppressive drugs.
- Surgical
- Aspiration or excision of brain abscesses that are large, accessible or not shrinking, and drainage of empyema or skin abscesses.
- Follow-up
- Repeat imaging to follow abscess size; blood counts, kidney function and potassium on long sulfonamide therapy.
Complications
- Brain abscesses with seizures or permanent deficits
- Empyema and chest wall spread
- Relapse after short courses
- Drug toxicity from prolonged therapy (bone marrow suppression, hyperkalaemia, rash)
Prognosis
Localised lung or skin disease usually responds well. Brain or disseminated infection carries high mortality, especially in profoundly immunosuppressed patients and when diagnosis is delayed.
Prevention
- Wound cleaning after soil contamination
- Sulfonamide prophylaxis used for Pneumocystis in transplant and HIV patients may lower the risk
Test yourself
Think of the answer, then tap the question to see it.
How does Nocardia appear on staining?
Gram-positive branching, beaded filaments that are weakly acid-fast on modified stain.
Which organ must be imaged in every patient with pulmonary nocardiosis?
The brain, because it is the most common site of spread.
What is the backbone antibiotic for nocardiosis?
A sulfonamide (trimethoprim-sulfamethoxazole).
How does Nocardia differ from Actinomyces?
Nocardia is aerobic and weakly acid-fast; Actinomyces is anaerobic and not acid-fast.
Related conditions
- Brain abscess
- Tuberculosis
- Lung abscess
- Actinomycosis
- Aspergillosis
- HIV infection and AIDS
- Mycetoma (actinomycetoma and eumycetoma)
- Lung cancer
- Pneumocystis pneumonia (PCP)
Educational information, not medical advice. For any symptom, see a health professional.
Sources: About Nocardiosis | Nocardiosis | CDC (Centers for Disease Control and Prevention, 2024).
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