Nontuberculous mycobacteria, commonly called NTM, are a large group of environmental bacteria that can cause chronic, hard-to-treat infections, most often in the lungs. Unlike their infamous cousin Mycobacterium tuberculosis, NTM are not spread person to person. Instead, they live in soil, water, and household plumbing, and people pick them up from everyday environmental exposures. Rates of NTM lung disease have been climbing worldwide, yet the infections remain underrecognized by patients and clinicians alike.
Where NTM Live
NTM are everywhere in the natural environment. They thrive in soils, rivers, lakes, and wetlands, but their real trick is colonizing human-engineered water systems. Municipal water pipes, hot tubs, swimming pools, and especially household showerheads provide ideal habitat. A large study of residential showerheads across the United States and Europe found that the genus Mycobacterium was consistently the most abundant type of bacteria in showerhead biofilms, with far higher concentrations in homes receiving chlorine-treated municipal water than in those on well water.1PubMed Central. Ecological Analyses of Mycobacteria in Showerhead Biofilms and Their Relevance to Human Health That finding is counterintuitive: you might expect treated water to be cleaner. But NTM have a lipid-rich outer membrane that acts as a hydrophobic barrier, making them resistant to chlorine and other water disinfectants that kill most competing bacteria.2PubMed. Nontuberculous mycobacteria in the environment Chlorination essentially clears the field for NTM, giving them less competition.
Their success in these environments also comes from an ability to form biofilms, stick to surfaces, and survive wide swings in temperature and nutrient availability.3PubMed Central. Ecology of Nontuberculous Mycobacteria Some species even survive inside free-living amoebae in water and soil, using these single-celled organisms as both shelter and a kind of training ground for infecting human immune cells later.4PubMed Central. Non-Tuberculous Mycobacteria: Molecular and Physiological Bases of Virulence and Adaptation to Ecological Niches Soil composition matters too. Research in Hawai’i, a geographic hot spot for NTM infections, has investigated how specific soil minerals and clays may serve as food sources or attachment surfaces that help NTM persist in the ground.5PubMed Central. Assessment of Soil Features on the Growth of Environmental Nontuberculous Mycobacterial Isolates from Hawai’i
How People Get Infected
Because NTM live in water and soil rather than in other people, the routes of infection differ from tuberculosis. You do not catch NTM from a cough across the room. Instead, the primary pathway is inhaling tiny water droplets or dust particles that carry the bacteria. Showers, hot tubs, humidifiers, and even garden soil can all generate aerosols containing NTM.6PubMed Central. Sources, transmission and hospital-associated outbreaks of nontuberculous mycobacteria: a review A number of outbreaks of respiratory illness, including a condition called hypersensitivity pneumonitis, have been traced to NTM-containing aerosols in workplaces, spas, and indoor water features.7PubMed Central. Mycobacterial aerosols and respiratory disease
Skin and soft-tissue infections follow a different route. These typically develop after NTM are introduced through a break in the skin: a surgical wound, a traumatic injury, a tattoo, or a cosmetic procedure like a pedicure spa bath.8PubMed. Nontuberculous Mycobacteria: Skin and Soft Tissue Infections Less commonly, people can ingest NTM in contaminated water or food. But for most patients, it is the lungs that bear the brunt.
Which Species Cause Disease
There are over 200 recognized NTM species, but only a handful cause the vast majority of human infections. The most common culprit worldwide is the Mycobacterium avium complex (MAC), a group of slow-growing species that predominates in pulmonary disease. Mycobacterium kansasii is another slow grower seen in lung infections, while Mycobacterium abscessus complex, a rapidly growing species, rounds out the top tier.9PubMed Central. Nontuberculous Mycobacteria-Overview The distinction between slow and rapid growers matters because it affects how the bacteria respond to antibiotics. M. abscessus in particular is notoriously difficult to treat, for reasons covered below.
Who Is at Risk
Most people inhale NTM regularly without ever getting sick. Healthy lungs and a functioning immune system handle these bacteria easily. Trouble starts when the lungs are already damaged or the immune system is compromised.
A meta-analysis of risk factors for NTM lung disease found that pre-existing respiratory conditions dramatically raise the odds. Bronchiectasis, a condition where airways are permanently widened and prone to mucus buildup, carried the strongest association, followed by a history of tuberculosis, interstitial lung disease, COPD, and asthma.10PubMed. Risk Factors for Nontuberculous Mycobacterial Pulmonary Disease: A Systematic Literature Review and Meta-Analysis Among immune-related risks, HIV infection and medications that suppress the immune system, especially anti-TNF biologics used for conditions like rheumatoid arthritis, and post-transplant immunosuppressive drugs, stand out.11PubMed. Underlying host risk factors for nontuberculous mycobacterial lung disease
There is also a recognized body-type phenotype. NTM lung disease disproportionately affects postmenopausal women who are tall, thin, and have a low body mass index. Some researchers suspect that certain chest-wall configurations or connective-tissue variants in this group create subtle airway-clearance problems. Genetic susceptibility research has identified several gene variants linked to how immune cells handle mycobacteria, including genes involved in the process by which macrophages digest bacteria internally and genes that regulate inflammatory signaling.12PubMed Central. Genetic Susceptibility to Nontuberculous Mycobacterial Pulmonary Disease: Is It the Chicken or the Egg? This is still an active area of study, but it helps explain why some seemingly healthy people develop NTM disease while others with the same exposures never do.
What NTM Lung Disease Looks Like
NTM lung disease tends to be slow and sneaky. Symptoms often build over months or years: a persistent cough, fatigue, occasional low-grade fevers, and gradual weight loss. Because these overlap with so many other conditions, patients commonly go through rounds of antibiotics for presumed ordinary infections before anyone considers NTM.
On imaging, two main patterns emerge. One looks similar to tuberculosis, with cavities (holes) in the upper lobes of the lung, typically in older men with underlying lung damage. The other, sometimes called the nodular-bronchiectatic form, features clusters of small nodules and widened airways, often concentrated in the middle lobe and lingula of the lung. CT scans of patients with this pattern consistently show bronchiectasis, small centrilobular nodules, and sometimes a characteristic “feeding bronchus” sign where a visible airway runs directly into a cavity.13AJR Am J Roentgenol. Hypothesis on the evolution of cavitary lesions in nontuberculous mycobacterial pulmonary infection: thin-section CT and histopathologic correlation The nodular-bronchiectatic form is the one more often seen in the thin, postmenopausal women described earlier, and it can progress very gradually.
Beyond the Lungs
Although the lungs are the most common target, NTM can infect skin, soft tissue, lymph nodes, bones, and joints. Skin infections typically appear as slow-growing nodules, abscesses, or ulcers at the site of a wound, surgical incision, or cosmetic procedure.8PubMed. Nontuberculous Mycobacteria: Skin and Soft Tissue Infections In one retrospective study of NTM skin and soft-tissue infections, about half the patients were immunocompromised, most commonly because of corticosteroids or disease-modifying antirheumatic drugs. Immunocompromised patients were more likely to develop disseminated disease, where the infection spreads to multiple sites.14Open Forum Infectious Diseases. Clinical Characteristics and Management of Non-Tuberculous Mycobacterial Skin and Soft Tissue Infections: A Retrospective Cohort Study
In children, the most recognizable NTM infection is cervical lymphadenitis, swollen lymph nodes in the neck that often look alarming but usually resolve well with surgery or, in some cases, observation. Disseminated NTM disease, where bacteria spread through the bloodstream, was historically seen almost exclusively in people with advanced HIV. Modern antiretroviral therapy has made that scenario much rarer, but disseminated NTM still occurs in people with severe genetic immunodeficiencies or those on heavy immunosuppression after organ transplants.
A Growing Problem Worldwide
NTM infections are becoming more common almost everywhere researchers look. A systematic review of global trends found that roughly four out of five studies reported increasing rates of NTM lung infection over time, with an overall annual rate of change of about 4% per year for both isolation rates and confirmed disease.15PubMed. Global trends of pulmonary infections with nontuberculous mycobacteria: a systematic review The reasons are probably a mix of better awareness and diagnostic testing, aging populations with more chronic lung disease, wider use of immunosuppressive medications, and possibly changes in water treatment practices and building plumbing design. Unlike tuberculosis, NTM infections are not reportable in most countries, so the true burden is almost certainly underestimated.
Getting a Diagnosis
Diagnosing NTM lung disease is not as simple as finding the bacteria once. Because NTM are so common in the environment, a single positive culture from a respiratory sample can be a contaminant or a transient colonizer rather than evidence of actual disease. Standard diagnostic guidelines require a combination of compatible symptoms, characteristic imaging findings, and at least two positive sputum cultures (or one from a bronchoscopy wash) to confirm pulmonary NTM disease. Meeting all three criteria matters because treating someone who does not truly have the disease means subjecting them to months of antibiotics they do not need.
Once NTM is suspected, identifying the exact species is critical because treatment differs sharply from one species to another. Culture remains the gold standard, but it is slow, sometimes taking weeks. Newer molecular methods have sped things up. A technique called MALDI-TOF mass spectrometry, which essentially identifies bacteria by their protein fingerprint, has shown excellent accuracy for NTM species identification when applied to cultured samples, achieving 100% species-level accuracy in several European reference laboratories.16IJID Regions. Incorporating direct molecular diagnostics in management algorithms for nontuberculous mycobacteria: Is it high time?
Why Treatment Is So Difficult
Treating NTM lung disease is one of the more frustrating challenges in infectious disease. The regimens are long, the drugs have significant side effects, and cure rates are far from guaranteed.
For the most common form, MAC lung disease, the recommended backbone is a combination of a macrolide antibiotic (azithromycin or clarithromycin), rifampin, and ethambutol, taken for at least 12 months after sputum cultures turn negative.17PubMed Central. Treatment of Mycobacterium avium Complex Pulmonary Disease In practice, that usually means 18 months or more of daily pills. Rates of relapse and reinfection after completing treatment remain high, and some patients need repeated courses over many years.
Side effects are a major barrier. Across published treatment cohorts, up to 70% of treated patients experienced at least one drug-related adverse event, and roughly 30 to 70% of those on daily regimens had to permanently stop at least one of their medications because of toxicity.18PubMed Central. Management of Drug Toxicity in Mycobacterium avium Complex Pulmonary Disease: An Expert Panel Survey Common problems include vision changes from ethambutol, liver irritation from rifampin, hearing loss from aminoglycosides, and gastrointestinal upset from macrolides. Managing these side effects is largely guided by clinical experience rather than robust evidence, because formal studies on how best to handle them are scarce.
The Drug Resistance Problem With M. abscessus
Mycobacterium abscessus deserves special attention because it is exceptionally hard to kill with antibiotics. Macrolide antibiotics like azithromycin and clarithromycin are the cornerstone of treatment, but most M. abscessus strains carry a gene called erm(41) that encodes inducible resistance. This means the bacteria may appear susceptible on initial lab testing, but as treatment continues, the gene kicks in and renders the macrolide ineffective.19PubMed Central. Dissecting erm(41)-Mediated Macrolide-Inducible Resistance in Mycobacterium abscessus Lab protocols now extend incubation to at least 14 days when testing macrolide susceptibility in M. abscessus, because most inducible resistance becomes apparent by day 7, but some strains take up to two weeks to reveal their true resistance profile.20PLOS ONE. Time-to-Detection of Inducible Macrolide Resistance in Mycobacterium abscessus Subspecies and Its Association with the Erm(41) Sequevar
Treatment for M. abscessus often requires intravenous antibiotics for months, sometimes combined with inhaled drugs, and outcomes remain poor compared with MAC disease. In refractory cases, surgical removal of the most affected lung tissue may be considered.
Inhaled Amikacin as an Emerging Option
For patients with MAC lung disease who fail standard oral therapy, an inhaled formulation of the antibiotic amikacin (amikacin liposome inhalation suspension, or ALIS) has emerged as an add-on option. In a randomized trial, adding ALIS to a standard multidrug regimen improved rates of sputum culture conversion compared with the standard regimen alone, though the primary endpoint of the trial was not met.21PubMed Central. Randomized Trial of Liposomal Amikacin for Inhalation in Nontuberculous Mycobacterial Lung Disease A subsequent larger study found that about 29% of patients who received ALIS plus their background therapy achieved culture conversion by month six, versus about 9% of those on background therapy alone, and a portion of those conversions were sustained and durable after treatment stopped.22CHEST. Amikacin Liposome Inhalation Suspension for Refractory Mycobacterium avium Complex Lung Disease: Sustainability and Durability of Culture Conversion and Safety of Long-term Exposure ALIS is not a cure-all; many patients still do not achieve conversion, and the inhaled drug can cause voice changes and cough. But for people who have run out of effective oral options, it represents genuine progress.
Reducing Your Exposure at Home
Because NTM infections come from the environment rather than other people, prevention strategies focus on reducing exposure in everyday settings. The most direct targets are household water and soil. For people already diagnosed with NTM lung disease, or those at high risk because of underlying lung conditions, several practical steps have been studied or recommended by experts:
- Shower ventilation: Running a dehumidifier in the bathroom, opening doors and windows during and after showering, or switching from a shower to a bath may reduce the aerosolized NTM you breathe in.23PubMed Central. Shower dehumidification to reduce nontuberculous mycobacteria aerosolization
- Hot water temperature: Raising your water heater above 130°F (55°C) may reduce NTM colonization in household plumbing, though this carries a scald risk that needs to be managed with mixing valves at the tap.24Annals of the American Thoracic Society. Reducing Human Exposure to Mycobacterium avium
- Point-of-use filters: Installing showerhead or faucet filters rated to block particles the size of mycobacteria can reduce exposure at the point where aerosols are generated.24Annals of the American Thoracic Society. Reducing Human Exposure to Mycobacterium avium
- Soil and garden precautions: Wearing a mask while gardening, potting plants, or working with mulch and compost can limit inhaled NTM from soil dust.
- Hot tub hygiene: Poorly maintained hot tubs are one of the better-documented sources of NTM aerosol exposure. Keeping hot tubs properly chlorinated or avoiding them entirely is reasonable for high-risk individuals.
Some researchers have proposed rethinking home design itself, suggesting that future building standards could incorporate the concept of a “healthy home” engineered environmental microbiome, where plumbing materials, water heating, and ventilation work together to reduce NTM-friendly conditions.25PubMed. Methods to reduce environmental nontuberculous mycobacteria exposure: revisiting the recent literature That idea is still at the conceptual stage, but it reflects how seriously the environmental-exposure angle is being taken.
The Toll on Daily Life
Living with NTM lung disease is not just a medical challenge, it is an ongoing disruption to ordinary life. A European patient survey found that about half of patients reported high restrictions in their daily activities, roughly a third experienced limitations at work, and over 40% cut back on social activities. Perhaps most strikingly, 82% reported increased feelings of depression or anxiety related to their disease.26PubMed Central. Insights from the European Nontuberculous mycobacterial pulmonary disease PAtient Disease Experience (ENPADE) survey- exploring disease burden and impact The combination of chronic cough, fatigue, medication side effects, and the uncertainty of a disease that may relapse creates a burden that standard quality-of-life measures tend to underestimate.
Financial and Healthcare Costs
The economic weight of NTM disease is substantial, and it comes from several directions: long courses of expensive medications, frequent clinic visits, imaging, lab work, and for some patients, hospitalizations and surgery. In a South Korean study tracking costs from 2015 to 2019, patients with NTM lung disease who required hospitalization incurred median total costs roughly 2.5 times higher than those managed as outpatients alone, with hospitalization driving most of the excess.27Emerging Infectious Diseases. Medical Costs of Nontuberculous Mycobacterial Pulmonary Disease, South Korea, 2015–2019 A nationwide Danish analysis painted an even broader picture, showing that patients’ healthcare costs in the year of diagnosis were roughly six times those of matched comparators, while their employment income was about half, reflecting both reduced work capacity and increased reliance on public benefits.28PubMed Central. Nontuberculous mycobacterial pulmonary disease: a nationwide cost analysis of healthcare costs, foregone earnings and public benefits in a universal healthcare setting
In the United States, hospital discharge data from 2001 through 2012 recorded over 20,000 hospitalizations for pulmonary NTM, with total associated hospital costs approaching $904 million, and those costs rose significantly over the study period.29PubMed Central. Hospital costs in the US for pulmonary mycobacterial diseases Given that incidence has continued climbing in the decade since, current figures are likely much higher.
NTM and the Tuberculin Skin Test
One practical wrinkle worth knowing about: NTM exposure can create false signals on screening tests designed for tuberculosis. The standard tuberculin skin test (TST) uses a protein mixture derived from mycobacteria, and because NTM share many proteins with the TB bacterium, someone exposed to environmental NTM may mount a low-level immune response to the test even without any TB infection. A study in BCG-naïve children demonstrated immune responses to the TB test protein in their blood despite having no reaction on the actual skin test, supporting the idea that environmental NTM prime the immune system without necessarily causing a positive TST.30PLOS ONE. The Tuberculin Skin Test (TST) Is Affected by Recent BCG Vaccination but Not by Exposure to Non-Tuberculosis Mycobacteria (NTM) during Early Life This overlap is one reason why interferon-gamma release assays, which use antigens more specific to TB, have become the preferred screening method in many settings. If you have ever had a borderline or weakly positive TB skin test with no clear TB exposure history, NTM cross-reactivity is one plausible explanation your doctor may consider.