Atypical Mycobacterial Infection (NTM)

What NTM are

Mycobacteria are a family of slow-growing bacteria with waxy cell walls. Mycobacterium tuberculosis causes TB and M. leprae causes leprosy. The other 190 or more species are called nontuberculous or "atypical." They live in soil, natural water, and biofilms in showerheads, hot tubs and pipes. People breathe them in as aerosols or get them through breaks in the skin. Most exposures cause no illness; disease develops when lung or immune defenses are weakened.

NTM lung disease has been increasing in the US, especially in older adults.

Types and symptoms

Lung disease

The most common form. Symptoms develop slowly over months to years:

• chronic cough, often with sputum
• tiredness and reduced exercise tolerance
• weight loss, low-grade fever and night sweats
• breathlessness
• coughing up blood occasionally

Two patterns are common:

• Nodular bronchiectatic disease: small nodules and widened airways (bronchiectasis), often in the middle lobe and lingula. Typical in postmenopausal women who are slim, sometimes with a curved spine or chest wall shape changes, and no smoking history.
• Fibrocavitary disease: cavities in the upper lobes, like TB, usually in older men with COPD or a smoking or alcohol history. It progresses faster.

Skin and soft tissue infection

• M. marinum ("fish tank granuloma"): red or purple bumps on the hands or arms after contact with aquariums or fish; may spread in a line up the arm.
• Rapid growers (M. abscessus, M. fortuitum, M. chelonae): infections after surgery, cosmetic procedures, tattoos, pedicures in whirlpool footbaths, or injections. Firm, red, draining nodules that do not respond to normal antibiotics.

Lymph node infection (lymphadenitis)

Mostly in children aged 1 to 5. A single, painless, swollen lymph node in the neck or under the jaw that gradually turns purple and may drain. The child is usually otherwise well. See lymphadenitis.

Disseminated infection

Spread through the blood, causing fever, weight loss, night sweats, diarrhea, anemia and enlarged liver and spleen. It occurs in advanced HIV (CD4 count below 50) and in people with rare immune defects or on strong immune-suppressing drugs.

Who is at risk

• lung disease: bronchiectasis, COPD, cystic fibrosis, previous TB, lung cancer
• older age, especially slim postmenopausal women
• weakened immunity: HIV, organ transplant, TNF inhibitors and other biologics, long-term steroids, inborn immune defects
• acid reflux and aspiration
• exposure to aerosols from hot tubs, showers and soil

Is NTM contagious?

Generally no. NTM are acquired from the environment, not from other people. The exception is M. abscessus in cystic fibrosis clinics, where some person-to-person transmission has been documented, so infection control precautions are used.

Diagnosis

Because NTM are common in the environment, a single positive sputum sample can be contamination. The ATS/IDSA criteria require:

1. Symptoms consistent with lung infection.
2. Imaging: a chest CT showing nodules with bronchiectasis or cavities.
3. Microbiology: the same NTM species grown from at least two separate sputum samples, or one bronchoscopy sample, or a lung biopsy.

Other conditions such as TB and lung cancer are ruled out. Skin and lymph node infections are diagnosed by culture and biopsy. Disseminated infection is diagnosed from blood cultures.

Treatment

Not everyone with NTM in their sputum needs immediate treatment. Mild, stable nodular disease may be monitored. Treatment is recommended for progressive or cavitary disease, significant symptoms, or positive smear results.

MAC lung disease

• Usually three antibiotics: a macrolide (azithromycin), ethambutol and a rifamycin (rifampin), taken three times a week for nodular disease or daily for cavitary disease.
• Inhaled amikacin may be added for refractory disease.
• Treatment continues for at least 12 months after sputum cultures become negative, often 15 to 18 months in total.

Other species

• M. abscessus: among the hardest to treat; IV and oral antibiotic combinations, sometimes with surgery.
• M. kansasii: responds well to rifampin, ethambutol and isoniazid or a macrolide.
• Skin infections: antibiotics for months, sometimes surgical removal of infected tissue or implants.
• Childhood lymph nodes: surgical removal of the node is usually curative.

Supporting care

Airway clearance techniques, treating reflux, nutrition support, and regular monitoring for side effects (hearing, vision, liver tests) are part of treatment. Specialist centers have the most experience.

Outlook

NTM lung disease is usually chronic. Treatment clears the infection in many people with MAC, but recurrence or reinfection is common. M. abscessus is harder to cure. Skin and lymph node infections usually resolve with appropriate treatment.

Prevention

People with bronchiectasis or weak immunity can reduce exposure by:

• avoiding hot tubs and indoor spas
• raising water heater temperature to at least 130 °F (55 °C) where safe
• cleaning or replacing showerheads regularly
• wearing a mask when gardening or handling potting soil
• wearing gloves when cleaning fish tanks

Frequently asked questions

What is an atypical mycobacterial infection?

It is an infection caused by mycobacteria other than tuberculosis and leprosy. These germs live in soil and water. They most often cause a slow lung infection in people with bronchiectasis or COPD, but can also infect skin, lymph nodes and, in people with weak immunity, the whole body.

Is nontuberculous mycobacteria contagious?

Usually not. People catch NTM from the environment, such as water aerosols and soil, rather than from each other. A rare exception is M. abscessus spreading between people with cystic fibrosis, which is why CF clinics use strict infection control.

What are the symptoms of MAC lung disease?

Symptoms include a chronic cough with sputum, tiredness, weight loss, night sweats, low-grade fever and breathlessness. They usually develop slowly over months to years and are often blamed on existing lung disease, which can delay diagnosis.

How long is treatment for NTM?

For MAC lung disease, treatment usually lasts at least 12 months after sputum cultures turn negative, often 15 to 18 months in total. Skin infections need several months of antibiotics. Childhood lymph node infections are usually cured by removing the node.

How is NTM different from tuberculosis?

Both are mycobacteria, but TB spreads from person to person through the air and is a public health concern, while NTM comes from the environment and rarely spreads between people. NTM also needs different antibiotics and often longer treatment.