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Nontuberculous mycobacterial lung disease

Nontuberculous mycobacteria (NTM) lung disease is not really a single disease entity, but a group of lung conditions.

NTM is a group of bacteria in the same family as the organism that causes tuberculosis (TB).

Over 140 NTMs have been identified, though only 20 to 30 have been linked to human disease.

These conditions vary in terms of their symptoms, severity, treatment and outcomes.

NTM lung disease is uncommon. However, it is increasingly being diagnosed, as the role NTMs play in human disease is better understood.

Where it's found

NTMs are found worldwide in the natural environment, particularly in the soil and water.

How it spreads

People are regularly exposed to NTMs via skin contact, from breathing in or swallowing the organisms.

It is not transmitted from person to person and is usually acquired from the environment.

In most individuals, this poses no risk of disease and the NTMs are readily killed or eliminated by the body’s immune defences.

Occasionally NTMs will not be eliminated from a person’s lungs, in which case there are 2 possible outcomes.

In some people, the NTMs survive in their airway temporarily or permanently without being the causative agent of symptoms.

These people:

  • are said to be colonised with NTMs and do not have NTM disease
  • people make up the largest group who culture NTMs from their sputum.

The second outcome for certain individuals may develop lung disease following exposure and infection with NTMs.

Who is at risk

People who have a higher risk of NTM lung disease include those who:

  • have existing chronic lung conditions, including:
    • emphysema
    • bronchiectasis
    • severe asthma
    • cystic fibrosis
  • are immunosuppressed, including:
    • chemotherapy patients
    • organ transplant recipients
    • HIV-positive people.

Rarely, persons without any of these risk factors may develop NTM lung disease.

People who get NTM lung disease repeatedly, over time, have the same NTM cultured from their sputum. They exhibit progressive clinical symptoms and radiological signs.

Symptoms

The symptoms of NTM lung disease usually develop slowly over weeks to months.

Specific symptoms can vary greatly among individuals.

They may be subtle, particularly if a patient normally experiences chronic symptoms from an existing underlying lung condition.

Eventually, people with NTM lung disease usually report at least some of the following symptoms:

  • shortness of breath, either new or worsening
  • productive cough for more than 3 weeks
  • weight loss
  • fevers
  • night sweats
  • coughing up blood
  • lethargy/fatigue.

Diagnosis

Making a diagnosis of NTM lung disease can be challenging and often takes several months.

This is because many patients already have pre-existing lung conditions with chronic symptoms.

In such situations, it can be difficult to determine whether new or worsening symptoms are simply due to:

  • progression of the pre-existing lung condition
  • something new entirely.

It is known that compromised lungs are frequently colonised by NTMs. But unless these NTMs are causing disease, antibiotic treatment will not be of any benefit.

Due to these challenges, the following 3 criteria must be satisfied before a diagnosis of NTM lung disease is made:

  • patient should report new or worsening symptoms over time
  • multiple sputum samples, taken several weeks apart, should consistently grow the same species of NTM bacteria in a laboratory
  • X-ray or CT scan of the lung should demonstrate abnormalities known to be associated with NTM lung disease.

Treatment

NTM lung disease requires a prolonged treatment course that often lasts longer than 12 months.

It is usually treated with a combination of 3 to 4 different antibiotics.

The specific choice of antibiotics will depend on the type of NTM and individual patient factors.

Most antibiotics are prescribed in oral tablet form, taken daily.

During this time, sputum samples are regularly collected to look for evidence of persistent or clearing infection.

Patients are usually reviewed on a monthly basis at a specialist clinic.

Regular blood tests and imaging are also required to monitor the response to treatment and detect any potential drug side effects.

While receiving treatment, if symptoms allow, patients may return to their regular activities, including work.

Treatment is usually continued until:

  • a patient’s symptoms have improved and
  • sputum samples have stopped growing NTM bacteria for at least 12 months.

Prevention

As NTMs are found in almost all natural environments, there are limited viable strategies to prevent exposure.

There are no vaccines against NTMs.

Information for health professionals

To find out more, go to the NT Health website.

Contact

Contact your nearest Centre for Disease Control on the NT Health website.