Nocardiosis (Nocardia Infection)

How Nocardia causes infection

Nocardia are bacteria that grow as branching threads, found worldwide in soil and decaying organic matter. Infection usually happens by:

• Breathing in contaminated dust, leading to lung infection
• Skin contamination through cuts, scrapes, thorns or puncture wounds, especially in gardeners and farm workers

From the lungs, infection can spread through the bloodstream, most often to the brain. It does not spread between people.

Who is at risk

• Solid organ and stem cell transplant recipients
• People taking long-term corticosteroids or other immune-suppressing drugs
• People with cancer, particularly blood cancers
• People with HIV with low CD4 counts
• People with diabetes, alcohol use disorder or chronic lung disease such as COPD or bronchiectasis

Skin nocardiosis can occur in otherwise healthy people after an injury.

Types and symptoms

Lung (pulmonary) nocardiosis

The most common form. Symptoms develop over days to weeks:

• Cough, sometimes with thick or bloody sputum
• Fever, night sweats and weight loss
• Shortness of breath and chest pain

It can look like pneumonia, tuberculosis, fungal infection or lung cancer, and may form a lung abscess.

Brain (central nervous system) nocardiosis

• Headache, confusion, seizures, weakness or vision changes
• Often from a brain abscess, which may develop slowly with few symptoms
• Can occur in people with lung infection who have no brain symptoms, which is why brain imaging is recommended

Skin (cutaneous) nocardiosis

• A red, swollen, painful sore or abscess at a wound site
• Nodules spreading up a limb along the lymph channels (lymphocutaneous form), similar to sporotrichosis
• Mycetoma: a chronic, deep infection with swelling and draining channels, usually of the foot, in tropical regions

Disseminated nocardiosis

Spread to two or more organs, including brain, skin, kidneys, eyes, joints and heart, mostly in people with severe immune suppression.

Diagnosis

• Samples: sputum, bronchoscopy washings, pus from abscesses or tissue biopsies.
• Laboratory testing: Nocardia appear as thin branching rods on Gram stain and are weakly acid-fast. Labs should be told nocardiosis is suspected, as cultures can take several days to weeks. Molecular methods identify the species, which helps choose antibiotics.
• Imaging: chest X-ray or CT for nodules, cavities or abscesses.
• Brain MRI: recommended for people with lung or disseminated infection, and for anyone with neurological symptoms.

Treatment

• Antibiotics: trimethoprim-sulfamethoxazole (TMP-SMX) is the main treatment. Severe or brain infections usually need combination IV antibiotics at first, such as imipenem, amikacin, ceftriaxone or linezolid, chosen according to species and susceptibility testing.
• Duration: typically at least 6 months for lung or skin infection in people with normal immunity, and 12 months or longer for brain or disseminated infection, or in people with weakened immunity.
• Surgery or drainage for large abscesses, including some brain abscesses.
• Reducing immune suppression where possible, in discussion with transplant or specialist teams.
• Monitoring for side effects of long-term antibiotics, including blood counts, kidney function and potassium.

Outlook

Localized skin infections in healthy people usually respond well to treatment. Lung nocardiosis has a good outlook when treated early. Brain and disseminated infections are more serious, with higher mortality, especially in people with severe immune suppression. Completing the full course of treatment is important to prevent relapse.

Prevention

• Wear gloves and protective clothing when gardening or working with soil, particularly if you have a weakened immune system.
• Clean cuts and scrapes promptly.
• Some transplant recipients take TMP-SMX to prevent pneumocystis pneumonia, which may also reduce the risk of nocardiosis.

Frequently asked questions

What is nocardiosis?

Nocardiosis is an infection caused by Nocardia bacteria found in soil and decaying plants. It usually affects the lungs but can spread to the brain, skin and other organs. It mostly affects people with weakened immune systems and requires long courses of antibiotics.

How do you get a Nocardia infection?

Most people breathe in Nocardia from dust or soil, causing a lung infection. Skin infections happen when soil enters a cut, scrape or puncture wound. Nocardiosis is not contagious and does not spread from person to person or from animals to people.

What are the symptoms of nocardiosis?

Lung infection causes cough, fever, night sweats, weight loss, shortness of breath and chest pain. Brain infection causes headaches, confusion, seizures or weakness. Skin infection causes a painful, swollen sore or abscess, sometimes with lumps spreading up a limb.

How long is treatment for nocardiosis?

Treatment usually lasts at least 6 months for lung or skin infections in people with healthy immune systems, and 12 months or longer for brain or widespread infection or in people with weakened immunity. Stopping early increases the risk of relapse.