Understanding environmental mycobacteria and chronic lung infection
Non-Tuberculous Mycobacterial Pulmonary Disease: Understanding the Disease
Non-tuberculous mycobacteria are environmental bacteria found in water, soil and aerosols. They can occasionally cause chronic pulmonary disease, particularly in people with bronchiectasis, chronic obstructive pulmonary disease, cystic fibrosis or impaired immunity. Finding NTM in a sputum sample does not always mean that treatment is required.
- NTM pulmonary disease
- MAC
- M. kansasii
- M. abscessus
- Sputum cultures
- Chest CT
- Antibiotic treatment
- Airway clearance
A positive culture is not automatically disease
NTM may represent environmental contamination, temporary airway presence or clinically important infection. Symptoms, CT findings and repeated microbiology must be interpreted together.
Treatment is species-specific
Different NTM species have different antibiotic susceptibility, clinical behaviour and prognosis. Precise laboratory identification is essential before treatment is selected.
What are non-tuberculous mycobacteria?
Non-tuberculous mycobacteria, or NTM, are mycobacterial species other than the Mycobacterium tuberculosis complex and Mycobacterium leprae. They are widely distributed in natural and engineered environments, particularly water and soil.
More than 190 NTM species and subspecies have been described. Many rarely cause human illness, while a smaller number are recognised pulmonary pathogens.
NTM are biologically related to the bacteria that cause tuberculosis, but NTM pulmonary disease is not tuberculosis. Diagnosis, transmission patterns and treatment regimens are different.
Exposure is common. Organisms may be encountered in soil, natural water, domestic water systems, shower aerosols and other environmental sources. Most exposed people never develop disease.
Inhaling NTM does not necessarily cause infection, and growing NTM from one sample does not necessarily establish progressive pulmonary disease.
How does NTM pulmonary disease differ from tuberculosis?
| Feature | NTM pulmonary disease | Pulmonary tuberculosis |
|---|---|---|
| Organisms | Numerous environmental NTM species | Mycobacterium tuberculosis complex |
| Usual source | Water, soil and environmental aerosols | Another person with infectious pulmonary or laryngeal TB |
| Person-to-person transmission | Generally not considered contagious in ordinary social contact | Can spread through the air |
| Public-health contact tracing | Not routinely required | May be required for infectious TB |
| Diagnosis | Requires compatible clinical, radiological and microbiological evidence | Based on clinical assessment and identification of the TB organism |
| Treatment | Species-specific multidrug regimens | Standardised combinations adjusted for susceptibility and clinical circumstances |
An important transmission qualification
Ordinary household transmission of NTM is not generally expected. However, healthcare-associated transmission of particular Mycobacterium abscessus strains has been reported between some people with cystic fibrosis. Specialist infection-control advice applies in those settings.
NTM species that commonly cause pulmonary disease
Mycobacterium avium complex
Members
MAC includes M. avium, M. intracellulare and several closely related organisms.
Clinical pattern
MAC may cause nodular-bronchiectatic disease or more destructive fibrocavitary disease.
Treatment principle
Macrolide susceptibility is central to regimen selection and prognosis.
Mycobacterium kansasii
Clinical pattern
It can cause upper-lobe cavitary disease that resembles pulmonary tuberculosis.
Susceptibility
Rifampicin susceptibility is particularly important before treatment.
Outlook
Rifampicin-susceptible disease often responds well to an appropriate multidrug regimen.
Mycobacterium abscessus complex
Members
Subspecies include M. abscessus, M. massiliense and M. bolletii.
Resistance
Intrinsic and inducible resistance can make treatment particularly difficult.
Management
Treatment normally requires an expert NTM team and may involve intravenous, inhaled and oral medicines.
Other pulmonary NTM
M. xenopi
May cause cavitary or progressive disease, particularly in people with structural lung disease.
M. malmoense
An established cause of pulmonary disease in the UK and northern Europe.
Unusual isolates
Rare species require expert microbiological interpretation because pathogenicity varies considerably.
Species identification matters
Laboratories should identify clinically significant isolates to species level and, for M. abscessus complex, usually to subspecies level. Treatment cannot safely be chosen from the label “NTM” alone.
Who is more likely to develop NTM pulmonary disease?
NTM pulmonary disease can occur without a previously recognised lung condition, but risk is higher when airway structure, mucus clearance or immune defence is impaired.
Bronchiectasis
Dilated airways retain mucus and create a favourable environment for persistent mycobacterial growth.
Chronic obstructive pulmonary disease
Emphysema, chronic bronchitis, smoking-related damage and corticosteroid exposure may increase susceptibility.
Cystic fibrosis
Thick secretions and chronic structural airway disease increase NTM isolation and pulmonary-disease risk.
Previous tuberculosis
Residual cavities and damaged lung tissue can predispose to later NTM disease.
Interstitial lung disease
Fibrotic structural change and immune-modifying treatment may increase vulnerability.
Alpha-1 antitrypsin deficiency
Associated emphysema and bronchiectasis may provide the structural conditions for infection.
Immune suppression
Transplantation, haematological disease, chemotherapy and some immune-modifying medicines can increase risk.
Anti-TNF therapy
TNF is important in mycobacterial immune defence. Blocking it can increase susceptibility to mycobacterial disease.
Low body weight
Low body mass and reduced nutritional reserve are frequently associated with nodular-bronchiectatic NTM disease.
Impaired mucus clearance
Primary ciliary dyskinesia and other mucociliary disorders may allow organisms to persist in the airways.
Gastro-oesophageal reflux or aspiration
Repeated microaspiration may contribute to airway inflammation and structural damage in selected patients.
Increasing age
NTM pulmonary disease is diagnosed more frequently in older adults, partly because structural lung disease becomes more common.
Bronchiectasis is one of the most important associated conditions. Read more about bronchiectasis diagnosis and treatment .
Primary ciliary dyskinesia and other inherited mucus-clearance disorders may also increase susceptibility. Read the introduction to primary ciliary dyskinesia .
Symptoms of NTM pulmonary disease
Symptoms often develop gradually and overlap with bronchiectasis, COPD, bacterial infection, fungal disease and other chronic lung conditions.
Persistent cough
Cough may be dry or productive and may become more frequent over months or years.
Sputum production
Daily mucus, increased sputum volume or recurrent changes in sputum colour can occur.
Fatigue
Persistent exhaustion and reduced stamina can be prominent even when respiratory symptoms appear modest.
Weight loss
Reduced appetite and unexplained weight loss can indicate more active or advanced disease.
Breathlessness
Exertional breathlessness may reflect airway obstruction, bronchiectasis, cavities or the underlying lung condition.
Fever or night sweats
Low-grade fever and night sweats may occur but are not present in every patient.
Chest discomfort
Some people experience an ache, tightness or pleuritic discomfort, although other causes must be considered.
Haemoptysis
Blood-streaked sputum or more substantial bleeding may occur from inflamed or bronchiectatic airways.
A chronic cough should be assessed systematically. Read about specialist chronic-cough investigation .
Unexplained breathlessness can also be assessed through the breathlessness diagnosis and treatment service .
Seek urgent medical help for:
- significant coughing of fresh blood;
- severe or rapidly worsening breathlessness;
- blue or grey lips or skin;
- collapse, fainting or new confusion;
- severe chest pain;
- very low or rapidly falling oxygen saturation;
- high fever with severe weakness or deterioration.
Call 999 for immediately life-threatening symptoms.
How is NTM pulmonary disease diagnosed?
Diagnosis requires a compatible combination of clinical symptoms, characteristic radiological abnormalities and microbiological evidence. One isolated sputum culture is often insufficient.
- Review symptoms and their progression Cough, sputum, weight, fatigue, breathlessness, fever and haemoptysis are compared with the patient’s usual baseline.
- Identify underlying lung disease Bronchiectasis, COPD, cystic fibrosis, previous TB, aspiration and immune disorders are assessed.
- Obtain high-quality sputum samples Multiple respiratory samples are collected on separate days for acid-fast bacillus microscopy and mycobacterial culture.
- Confirm the species Clinically significant isolates should be identified precisely, because pathogenicity and treatment differ.
- Arrange chest imaging High-resolution CT assesses bronchiectasis, small nodules, mucus plugging, cavities, consolidation and disease distribution.
- Assess susceptibility Drug-susceptibility testing is interpreted according to the species and the medicines for which laboratory results are clinically meaningful.
- Exclude alternative diagnoses Tuberculosis, bacterial infection, fungal disease, malignancy and inflammatory disorders may produce similar findings.
- Discuss clinical significance The respiratory physician and microbiologist decide whether the isolate represents contamination, transient presence or active NTM pulmonary disease.
| Sample pathway | Microbiological evidence | Important qualification |
|---|---|---|
| Expectorated sputum | The same NTM species is usually cultured from at least two separate sputum samples | Samples should be collected on different occasions and interpreted with symptoms and CT findings |
| Bronchoscopy | A positive bronchial wash or bronchoalveolar lavage culture may satisfy microbiological criteria | Bronchoscopy is not automatically required when adequate sputum samples are available |
| Lung biopsy | Compatible histology plus a positive tissue or respiratory culture may support diagnosis | Biopsy is reserved for selected cases and is not routine |
Meeting diagnostic criteria does not automatically mean treatment
Diagnostic criteria establish that NTM pulmonary disease is present. The decision to begin antibiotics is separate and considers symptoms, progression, species, cavities, smear status, treatment toxicity and patient preference.
What can a chest CT show?
Nodular-bronchiectatic disease
Typical findings
Bronchiectasis, small nodules, tree-in-bud change and mucus plugging may be present.
Distribution
The middle lobe and lingula are often involved, although disease can be more widespread.
Progression
Some cases progress slowly, while others become symptomatic or structurally destructive.
Fibrocavitary disease
Typical findings
Upper-lobe cavities, fibrosis, volume loss and surrounding inflammatory change may occur.
Clinical setting
More common in people with COPD, emphysema or previous structural lung damage.
Significance
Cavitary disease is generally associated with a greater risk of progression and poorer outcomes.
Other radiological patterns
Consolidation
Airspace opacities may occur but require assessment for bacterial infection and other causes.
Solitary nodule
NTM can occasionally be identified in a resected pulmonary nodule without more extensive disease.
Overlap
NTM may coexist with emphysema, fibrosis, fungal disease or another cause of bronchiectasis.
Read more about chest X-ray and CT imaging .
Sputum cultures, induced sputum and bronchoscopy
Expectorated sputum
Naturally produced lower-respiratory sputum is usually the simplest and least invasive sample.
Induced sputum
Nebulised saline can help produce a sample when sputum is not available spontaneously.
Bronchoscopy
Bronchial washing or lavage may be considered when suspicion remains high but adequate sputum cannot be obtained.
Culture time
Mycobacterial culture may take several weeks because many NTM species grow slowly.
Acid-fast microscopy
Smear positivity can indicate a higher organism burden but cannot identify the species by itself.
Repeat sampling
Serial cultures help establish diagnosis, monitor progression and determine culture conversion during treatment.
Recurrent or complex respiratory infection can be assessed through the chest-infection diagnosis and treatment service .
Does everyone with NTM pulmonary disease need antibiotics?
No. Some patients have mild, stable disease in which careful observation, airway clearance and treatment of the underlying lung condition may initially be more appropriate than a prolonged multidrug regimen.
Reasons favouring treatment
Progressive symptoms, weight loss, radiological progression, cavities, smear positivity or a more pathogenic species may favour antibiotic therapy.
Reasons favouring observation
Mild symptoms, limited stable CT abnormalities, low organism burden or substantial treatment risk may support monitoring.
Species pathogenicity
M. kansasii is generally considered more likely to represent disease than some less pathogenic environmental isolates.
Patient priorities
Expected benefit, treatment burden, occupation, fertility, travel and quality of life should form part of shared decision-making.
Observation may include regular symptoms review, weight measurement, sputum cultures, lung-function testing and repeat imaging so that progression can be identified promptly.
Antibiotic treatment for NTM pulmonary disease
NTM treatment usually requires several antibiotics because single-drug therapy can fail and promote clinically important drug resistance. The exact regimen depends on species, susceptibility, disease severity and previous treatment.
| Organism | General treatment principle | Important considerations |
|---|---|---|
| Macrolide-susceptible MAC | Usually a macrolide, rifampicin or rifabutin, and ethambutol | Daily or intermittent frequency depends on cavitation, severity and the clinical phenotype |
| Severe or cavitary MAC | Daily oral treatment, sometimes with initial intravenous or inhaled aminoglycoside therapy | Specialist assessment is required because toxicity and treatment burden are greater |
| M. kansasii | A rifampicin-based three-drug regimen | Rifampicin susceptibility is essential; alternatives are needed for resistant disease |
| M. xenopi | A multidrug regimen selected according to guidance, susceptibility and severity | Cavitary or severe disease may require additional parenteral therapy |
| M. abscessus complex | An initial intensive phase followed by a prolonged continuation regimen using several active agents | Subspecies, erm(41) function, macrolide susceptibility and expert advice are critical |
Do not treat MAC with a macrolide alone
Macrolide monotherapy or an inadequate companion-drug regimen can select macrolide resistance. Macrolide-resistant MAC is substantially more difficult to treat.
Never copy another patient’s NTM regimen
A combination appropriate for MAC may be ineffective or unsafe for M. abscessus, M. kansasii or another species. Treatment must be based on the confirmed organism, susceptibility results, disease pattern and individual health risks.
How long does NTM treatment last?
Treatment duration is generally measured from sputum culture conversion rather than simply from the date on which antibiotics were started.
Culture conversion
This usually means that serial sputum cultures have become negative and remain negative according to the specialist treatment protocol.
Twelve months after conversion
Many slowly growing NTM regimens continue for at least 12 months after culture conversion.
Total duration varies
Delayed conversion, intolerance, resistance, cavities or recurrent positive cultures can extend the treatment period.
M. abscessus is different
Duration is especially individualised because microbiological cure may be difficult and drug toxicity can limit options.
Feeling better does not mean treatment should stop
Symptoms can improve before cultures remain consistently negative. Stopping treatment early may increase recurrence or resistance risk.
Monitoring during NTM treatment
- Sputum cultures Regular samples monitor microbiological response and establish the date of culture conversion.
- Symptoms and weight Cough, sputum, fatigue, breathlessness, appetite and body weight are reviewed over time.
- Lung-function testing Spirometry and other tests can identify physiological improvement or deterioration.
- Chest imaging Chest X-ray or CT is repeated when needed to assess structural response or progression.
- Blood tests Liver function, kidney function and blood counts are monitored according to the regimen.
- Vision testing Ethambutol can affect colour vision and visual acuity, requiring baseline advice and prompt review of symptoms.
- Hearing assessment Amikacin and other aminoglycosides can affect hearing and balance.
- ECG and interaction review Several NTM medicines can prolong the QT interval or interact with other treatments.
| Medicine | Important adverse effects | Monitoring considerations |
|---|---|---|
| Azithromycin or clarithromycin | Gastrointestinal effects, hearing effects, liver injury and QT prolongation | ECG, hearing, liver function and interaction review where appropriate |
| Rifampicin or rifabutin | Liver injury, blood abnormalities and orange-red body-fluid discolouration | Major drug-interaction review and blood monitoring |
| Ethambutol | Optic neuropathy with impaired acuity or colour vision | Baseline vision assessment and urgent review of visual change |
| Amikacin | Hearing loss, balance disturbance and kidney injury | Audiology, kidney function and serum levels when indicated |
| Clofazimine | Skin discolouration, gastrointestinal effects and QT prolongation | ECG and clinical monitoring |
| Linezolid | Low blood counts, neuropathy, optic toxicity and medicine interactions | Blood count, neurological and visual monitoring |
Contact the treatment team promptly for:
- new blurred vision or altered colour vision;
- new hearing loss, ringing in the ears or balance problems;
- yellow skin or eyes;
- severe vomiting or inability to take treatment;
- unusual bruising or bleeding;
- new numbness, burning or weakness;
- palpitations, fainting or severe dizziness;
- a widespread rash, blistering or facial swelling.
Airway clearance and treatment of underlying lung disease
Antibiotics are only one part of NTM management. Retained mucus, bronchiectasis, reflux, poor nutrition and other treatable factors should also be addressed.
Respiratory physiotherapy
An individualised airway-clearance technique can improve mucus drainage and support sputum sampling.
Hypertonic saline
Nebulised saline may help hydrate secretions and make sputum easier to clear in selected patients.
Exercise
Regular activity supports airway clearance, muscle strength, cardiovascular fitness and wellbeing.
Nutrition
Maintaining or restoring body weight can improve treatment resilience and general health.
Reflux and aspiration
Clinically significant reflux or swallowing dysfunction may require investigation and targeted management.
Smoking cessation
Stopping smoking reduces additional airway injury and supports long-term respiratory health.
Is surgery ever used?
Lung resection is considered only in selected patients and should be planned by an experienced multidisciplinary team. It is usually combined with appropriate antibiotic treatment.
Localised disease
Surgery is more feasible when the main disease burden is confined to a resectable part of one lung.
Persistent positive cultures
Resection may be considered when microbiological response remains poor despite an appropriate regimen.
Drug resistance
Macrolide-resistant MAC or difficult M. abscessus disease may prompt surgical consideration in suitable patients.
Severe haemoptysis
Recurrent or life-threatening bleeding may require embolisation, surgery or another urgent intervention.
Surgery is not a substitute for specialist antimicrobial care
Cardiopulmonary fitness, nutritional status, disease distribution and the likelihood of leaving active disease behind must all be assessed before resection.
Environmental exposure and practical precautions
NTM are common in water and soil, so complete avoidance is impossible. Evidence that specific household changes prevent disease recurrence remains limited, and recommendations should be proportionate.
Shower aerosols
Domestic water aerosols are a potential exposure source, but ordinary shower use should not be stopped without individual specialist advice.
Hot tubs and spas
Warm aerosolised water can contain high NTM concentrations and may warrant avoidance in susceptible patients.
Gardening
Soil and potting mix can generate dust. Dampening dry material and avoiding heavy dust exposure may be reasonable.
Masks and ventilation
A well-fitting mask and good ventilation may reduce intense soil or aerosol exposure during selected activities.
Do not pursue extreme environmental sterilisation
NTM cannot be eliminated completely from normal surroundings. Complex water-system modifications or major lifestyle restrictions should be discussed with an NTM specialist because evidence of benefit is uncertain.
Living with NTM pulmonary disease
- Take medicines exactly as prescribed Irregular dosing or stopping individual drugs can reduce efficacy and promote resistance.
- Report side effects early Many adverse effects can be managed more safely when identified promptly.
- Submit sputum regularly Cultures are central to measuring microbiological response.
- Continue airway clearance Physiotherapy remains important during and after antibiotic treatment.
- Protect nutrition Monitor weight and seek dietetic support when appetite or weight declines.
- Remain active Exercise can support endurance, mucus clearance and emotional wellbeing.
- Keep a medicine list NTM regimens have many interactions, so all clinicians and pharmacists should know which medicines are being taken.
- Seek psychological support Long treatment, uncertainty and medicine toxicity can affect mood, relationships and quality of life.
Patient support
NTM Patient Care UK provides information and peer support for people living with NTM infection and their families.
What happens after treatment?
Continued follow-up
Symptoms, sputum and imaging may continue to be monitored after the antibiotic course ends.
Recurrence
NTM can recur because of relapse with the original strain or reinfection from a new environmental strain.
Ongoing bronchiectasis care
Structural airway disease does not disappear when cultures become negative, so airway clearance and infection prevention remain important.
Reassessment of new symptoms
A new cough or deterioration should not automatically be assumed to be recurrent NTM; bacterial, viral and other causes remain possible.
Conclusion
Non-tuberculous mycobacteria are environmental organisms found particularly in water and soil. Exposure is common, but pulmonary disease develops in only a small proportion of people.
Bronchiectasis, COPD, cystic fibrosis, previous tuberculosis, impaired mucus clearance and immune suppression can increase susceptibility.
Symptoms include chronic cough, sputum, fatigue, breathlessness, weight loss, fever, night sweats and haemoptysis, but these overlap with many other respiratory conditions.
Diagnosis requires compatible symptoms, chest imaging and microbiology. The same organism is usually required from repeated sputum samples unless an alternative accepted sampling pathway is used.
Not everyone who meets diagnostic criteria requires immediate antibiotics. The decision depends on symptoms, radiological progression, cavities, organism burden, species, treatment risks and patient preference.
When treatment is needed, it involves a species-specific multidrug regimen with regular sputum, blood, vision, hearing and cardiac monitoring. Many regimens continue for at least 12 months after culture conversion.
Patients with repeated NTM-positive sputum cultures, unexplained bronchiectasis, progressive CT abnormalities or difficult treatment decisions can arrange a specialist respiratory infection assessment.
Frequently asked questions
Is NTM pulmonary disease the same as tuberculosis?
No. NTM are environmental mycobacteria. Tuberculosis is caused by the Mycobacterium tuberculosis complex and has different transmission, public-health and treatment implications.
Is NTM pulmonary disease contagious?
It is not generally considered contagious during ordinary social contact. Particular M. abscessus transmission concerns apply in some cystic-fibrosis healthcare settings.
Does one positive sputum sample mean I have NTM disease?
Usually not. A single isolate may represent contamination or temporary airway presence. Symptoms, CT imaging and repeat cultures are normally required.
Can NTM be present without causing illness?
Yes. NTM can sometimes be isolated without evidence of progressive pulmonary disease.
Why are at least two sputum cultures often required?
NTM are common in the environment. Repeated isolation of the same species makes clinically significant airway infection more likely.
Does everyone diagnosed with NTM-PD need antibiotics?
No. Mild stable disease may initially be monitored, while progressive symptoms, cavities or increasing organism burden may favour treatment.
Why are several antibiotics required?
NTM are difficult to eradicate, and inadequate single-drug therapy can select resistance.
How long does treatment last?
Many regimens continue for at least 12 months after sputum culture conversion. Total duration varies substantially.
What is culture conversion?
It means that serial sputum cultures have become negative according to the specialist monitoring protocol.
Can NTM return after successful treatment?
Yes. Recurrence may represent relapse of the original infection or reinfection with a new environmental strain.
Can NTM cause bronchiectasis?
NTM inflammation can worsen airway damage, while pre-existing bronchiectasis also increases susceptibility. The relationship can therefore operate in both directions.
Why is ethambutol vision monitoring important?
Ethambutol can rarely damage the optic nerves. New blurred vision or altered colour perception requires urgent advice.
Why is hearing monitored during amikacin treatment?
Amikacin can damage hearing or balance function, sometimes permanently, particularly with higher cumulative exposure.
Should I stop showering or gardening?
Not routinely. Complete avoidance of environmental NTM is impossible. Practical precautions should be individualised rather than extreme.
Can airway clearance help?
Yes. Airway clearance is an important part of care when mucus retention or bronchiectasis is present, whether or not antibiotic treatment is started.
Is surgery commonly required?
No. It is reserved for selected patients with sufficiently localised disease, acceptable surgical risk and a clear specialist rationale.
References and further information
- British Thoracic Society. Guideline for the management of non-tuberculous mycobacterial pulmonary disease. View the BTS NTM guideline
- Daley CL, Iaccarino JM, Lange C, et al. Treatment of nontuberculous mycobacterial pulmonary disease: an official ATS/ERS/ESCMID/IDSA clinical practice guideline. View the international treatment guideline
- NTM Network UK. Standards of Care for people living with non-tuberculous mycobacterial disease in the UK. View the UK NTM Standards of Care
- NTM Network UK. Patient support and treatment information. View NTM patient-support resources
- London Chest Specialist. Bronchiectasis diagnosis and treatment. Read about specialist bronchiectasis care
- London Chest Specialist. Chronic-cough specialist assessment. Read about chronic-cough investigation
- London Chest Specialist. Chest-infection diagnosis and treatment. Read about recurrent and complex chest infections
- London Chest Specialist. Breathlessness diagnosis and treatment. Read about specialist breathlessness assessment
- London Chest Specialist. Chest imaging. Read about spirometry and respiratory physiology
