NTM lung disease is a chronic infection caused by a group of bacteria called nontuberculous mycobacteria, which are found naturally in water, soil, and household plumbing. Unlike tuberculosis, which is caused by a closely related bacterium, NTM infections are not spread from person to person. Instead, people pick up these bacteria from their environment, typically by breathing in contaminated water droplets or dust particles. The disease affects roughly 3.8 per 100,000 people per year in the United States, with rates climbing as people age.
How NTM Differs From Tuberculosis
The “nontuberculous” label exists because these mycobacteria belong to the same family as the germ that causes TB, and the two infections can look similar on a chest X-ray or CT scan. But the similarities mostly end there. TB spreads through the air when an infected person coughs or sneezes. NTM does not pass between people. You cannot catch it from a family member, coworker, or anyone else who has it.
NTM bacteria live in the environment, not in human hosts. They thrive in water-associated biofilms (the slimy layers that coat the insides of pipes and faucets), in soil, and even in potting mix. Research from Hawai’i has found clinically relevant NTM species in garden soil and kitchen sink biofilms from ordinary households. In Japan, NTM isolated from residential soil has been genetically matched to the bacteria causing lung infections in the people living there. This means your own yard or plumbing system can be a source of exposure.
Which Bacteria Cause It
There are dozens of NTM species, but a handful cause the vast majority of lung infections. The most common is Mycobacterium avium complex (MAC), a group of slow-growing species that accounts for most cases worldwide. Mycobacterium abscessus is another major culprit, and it tends to be more aggressive and harder to treat. Mycobacterium kansasii rounds out the list of frequently encountered species, though others like Mycobacterium chimaera and Mycobacterium intracellulare also appear in clinical samples.
Symptoms
NTM lung disease develops slowly, and its symptoms overlap with many other respiratory conditions, which is one reason it often goes undiagnosed for months or years. The hallmark is a persistent cough that doesn’t resolve with standard treatments. Beyond that, symptoms include:
- Coughing up blood
- Shortness of breath
- Chest pain
- Fatigue that feels disproportionate to activity level
- Night sweats
- Low-grade fever
- Unexplained weight loss and loss of appetite
- Frequent respiratory illnesses
- Wheezing
Many people initially assume they have recurring bronchitis or a lingering cold. The vague, nonspecific nature of these symptoms means NTM lung disease is often only considered after other explanations have been ruled out.
Who Is Most at Risk
NTM bacteria are everywhere, yet most people who breathe them in never get sick. The infection takes hold primarily in people whose lungs are already compromised or whose immune defenses have a gap.
Bronchiectasis, a condition where the airways are permanently widened and scarred, carries the strongest association. In a large meta-analysis published in CHEST, people with bronchiectasis had more than 21 times the odds of developing NTM lung disease compared to those without it. Bronchiectasis is so closely linked to NTM that it appears in nearly all patients who have the non-cavitary form of the disease. COPD raised the odds about sixfold, a history of tuberculosis about 13-fold, and interstitial lung disease (scarring of lung tissue) about sixfold. Even asthma roughly quadrupled the risk.
Certain medications and conditions beyond the lungs also matter. Regular use of inhaled corticosteroids, common in asthma and COPD management, was associated with about four and a half times the odds of NTM lung disease. People with solid tumors showed elevated risk as well, though this may relate to the immune suppression from cancer treatment rather than the cancer itself. Gastroesophageal reflux disease (GERD) is widely considered a risk factor because stomach contents can be aspirated into the lungs, and it has been linked to higher bacterial loads and more severe imaging findings.
Demographically, the disease is more common in women than men, more common in older adults, and in the U.S., pulmonary NTM incidence is highest among non-Hispanic Asian persons.
How It’s Diagnosed
Diagnosing NTM lung disease requires meeting a specific set of criteria established by a consortium of international medical societies. Finding NTM in a single sputum sample is not enough for a diagnosis, because these bacteria are so common in the environment that a single positive result could simply reflect contamination.
To confirm the diagnosis, the same NTM species needs to be isolated in at least two separate sputum samples collected a week or more apart. This microbiologic evidence must also line up with compatible findings on imaging (typically a CT scan showing nodules, cavities, or bronchiectasis) and clinical symptoms consistent with the disease. Meeting all three criteria, clinical, radiographic, and microbiologic, is necessary because some people harbor NTM in their airways without ever developing progressive disease.
Treatment
NTM lung disease requires a combination of multiple antibiotics taken for a long time. Monotherapy doesn’t work here; the bacteria develop resistance quickly when exposed to a single drug. For MAC infections, the backbone of treatment is a macrolide antibiotic (which blocks bacterial protein production) combined with a drug that disrupts cell metabolism and a third drug that interferes with the bacteria’s ability to copy genetic material. Treatment typically lasts 12 to 18 months total, and the clock doesn’t start when you begin taking pills. Guidelines recommend continuing for 12 months after achieving culture conversion, which is defined as three consecutive negative sputum cultures.
During treatment, sputum samples are collected every four to eight weeks to track whether the bacteria are responding. If cultures remain positive after six months on a multi-drug regimen, an inhaled form of an additional antibiotic can be added to the mix. For people with cavitary disease (where the infection has created holes in the lung tissue), injectable antibiotics may be part of the initial regimen.
Infections caused by Mycobacterium abscessus are notably more difficult to treat. They are more likely to resist standard antibiotics and more likely to result in treatment failure.
Recurrence After Treatment
Even after successful treatment, NTM lung disease comes back in a significant number of people. Recurrence rates for MAC infections range from 30% to 50%, and the majority of these recurrences are reinfections from the environment rather than a relapse of the original infection. This distinction matters: it means the bacteria weren’t hiding in your lungs waiting to resurge. Instead, you were exposed again from water, soil, or another environmental source and became reinfected.
Recurrence rates vary based on the species involved, the patient’s age, and any underlying lung conditions. Mycobacterium abscessus infections carry a higher likelihood of both treatment failure and recurrence. Because reinfection drives most recurrences, some clinicians discuss environmental modifications with patients, such as avoiding hot tubs, being cautious with potting soil, and considering water filtration, though the effectiveness of these measures hasn’t been established in clinical trials.