Nontuberculous mycobacterial lung disease
NTM stands for nontuberculous mycobacteria. NTMs are 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. NTM lung disease is not really a single disease entity, but a group of lung conditions caused by a range of NTMs.
These conditions vary in terms of their symptoms, severity, treatment and outcomes. NTM lung disease is uncommon, however the condition is increasingly being diagnosed, as the role NTMs play in human disease is better understood.
Who gets NTM lung disease
NTMs are found worldwide in the natural environment, particularly in the soil and water.
People are regularly exposed to NTMs via skin contact, from breathing in or swallowing the organisms. 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 either temporarily or permanently without being the causative agent of symptoms. These persons are said to be colonised with NTMs and do not have NTM disease. These people make up the largest group who culture NTMs from their sputum.
The second outcome for certain individuals, however, may develop lung disease following exposure and infection with NTMs. Those with existing chronic lung conditions such as emphysema, bronchiectasis, severe asthma and cystic fibrosis are at higher risk of NTM disease.
Persons who are immunosuppressed such as those undergoing chemotherapy, organ transplant recipients and persons with HIV are also at increased risk, both for lung disease and NTM infection of multiple other organs. Rarely, persons without any of these risk factors may also develop NTM lung disease.
People with NTM lung disease repeatedly, over time, have the same NTM cultured from their sputum and exhibit progressive clinical symptoms and radiological signs of lung disease.
The symptoms of NTM lung disease usually develop slowly over weeks to months. Specific symptoms can vary greatly among individuals and 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
- night sweats
- coughing up blood
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 or due to 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.
Because of these challenges, 3 criteria must be satisfied before a diagnosis of NTM lung disease is made:
- A 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.
- Imaging of the lung, either on e.g. X-ray or CT scan, should demonstrate abnormalities known to be associated with NTM lung disease.
NTM lung disease 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. While receiving treatment, if symptoms allow, patients may return to their regular activities, including work.
NTM lung disease requires a prolonged treatment course that often lasts longer than 12 months. 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.
Treatment is usually continued until a patient’s symptoms have improved and sputum samples have stopped growing NTM bacteria for at least 12 months.
Can NTM infection spread to others and is there any prevention
NTM lung disease is not transmitted from person to person.
NTM infection is usually acquired from the environment. As these organisms are found in almost all natural environments, there are limited viable strategies to prevent exposure to the NTM organisms. There are no vaccines against NTM disease.
For more information contact your nearest Centre for Disease Control.
Last updated: 20 March 2020
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