• Also Known As:
  • NTM
  • Mycobacteria other than tuberculosis
  • MOTT
  • Atypical Mycobacteria
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What are nontuberculous mycobacteria?

Nontuberculous mycobacteria (NTM) are a diverse group of bacteria that include more than 150 different species, some of which can infect and cause illness in humans. The term nontuberculous mycobacteria refers to all the species in the family of mycobacteria that may cause human disease but that do not cause tuberculosis (TB).

These bacteria are common throughout the world, thriving in soil and water – including rivers and swamps, treated drinking water, swimming pools, hot tubs, humidifiers, aquariums/fish tanks, and garden soils – in both rural and urban settings. Significantly, NTM often contaminate the water supplies of hospitals and other medical facilities. Because they are protected by their waxy, fatty (lipid-rich) cell walls, NTM are resistant to usual disinfectants, water treatment measures, and antibiotics.

Almost half of the nontuberculous mycobacteria species identified are associated with opportunistic infections in animals and humans, and several have caused periodic outbreaks. The exact ways in which NTM enter a person has not been identified, but inhaling contaminated air or water droplets, drinking contaminated water, and direct contact with NTM through breaks in the skin or the accidental use of contaminated medical equipment (catheters, endoscopes, bronchoscopes) are considered the most likely routes of exposure. Unlike M. tuberculosis, the organism that causes tuberculosis, NTM are not passed from person to person (or animal to human).

Because NTM exist in the environment, nearly everyone will be exposed to some of these organisms, but most will not develop clinical signs of infection. For reasons that are not fully understood, people with weakened immune systems, such as those with AIDS and transplant recipients, people with pre-existing lung damage from smoking or previous tuberculosis, for example, and people with lung diseases such as emphysema, COPD, or cystic fibrosis are prone to NTM infections.

Most often, NTM infections develop in the lungs and can lead to severe lung disease in some individuals. NTM infections also occur in the lymph nodes, bones, skin, and soft tissues. NTM infections may be limited (localized) to one part of the body or they may spread (disseminate) throughout the body. NTM infections can be challenging and time-consuming to treat since the organisms may be resistant to commonly prescribed antibiotics.


About Nontuberculous Mycobacteria

Diseases caused by NTM

To date, more than 150 different nontuberculous mycobacteria (NTM) species have been identified. Not all of those species are known to cause disease in humans. The table below lists 6 clinical conditions that are caused by NTM infection and the species most often associated with those conditions.

Condition Common causes
Lung (pulmonary) disease, especially in adults M. avium complex (MAC), M. kansasii, M. abscessus
Cervical lymphadenitis (infection of the lymph nodes in the neck), especially in children M. avium, M. intracellulare
Skin and soft tissue disease M. fortuitum, M. chelonae, M. abscessus, M. marinum
Skeletal (bones, joints, tendons) disease M. marinum, M. avium complex, M. kansasii, M. fortuitum group, M. abscessus, M. chelonae
Widespread (disseminated) infections, especially in people who are HIV-positive or have weakened immune systems HIV-infected person: M. avium, M. kansasii
Non-HIV-infected person: M. abscessus, M. chelonae
Catheter-related bloodstream infections M. fortuitum, M. abscessus, M. chelonae

Signs and Symptoms

The symptoms associated with nontuberculous mycobacteria (NTM) infections depend on which part(s) of the body are involved. Lung (pulmonary) infections may cause tuberculosis-like symptoms, including:

  • Chronic cough, sometimes with bloody sputum
  • Fever
  • Chills
  • Weight loss
  • Weakness, fatigue

Skin-related NTM infections may cause persistent sores, boils, ulcers, and granulomas. Infections affecting lymph nodes may cause inflammation in the node(s).

All of these symptoms may also be seen in a variety of other conditions. The diagnosis of most NTM infections depends on the positive identification of mycobacteria in body fluids or tissues.


The diagnosis of nontuberculous mycobacteria (NTM) disease can be complex. Since nearly everyone is exposed to NTM, the goals of testing are to distinguish between evidence of previous exposure to NTM and a true NTM infection that requires treatment. According to a joint statement published by the American Thoracic Society and the Infectious Diseases Society of North America, a workup for patients suspected of having NTM lung disease should include, at minimum, the following:

  1. Chest x-ray and/or high-resolution CT scan
  2. Three of more sputum samples for acid-fast bacilli (AFB) analysis
  3. Exams and tests to rule out other disorders, such as tuberculosis

Laboratory Tests

Mycobacterial testing — these are the primary methods used to detect NTM infections and to rule out tuberculosis as a possible cause of a person’s symptoms. (See the article on acid-fast bacilli (AFB) testing.) The sample(s) collected for analysis depend on the part(s) of the body that the healthcare practitioner suspects are infected. For suspected lung infections, three or more sputum samples are collected early in the morning on different days. If the affected person is unable to produce sputum, a bronchoscope may be used to collect fluid during a procedure called a bronchoscopy. For suspected infections in other parts of the body, washings/aspirates, swabs of the infected area, fluids and/or tissue samples (biopsy) may be collected for testing. Testing may include:

  • AFB smear — a microscopic examination of a specimen that has been stained to detect acid-fast bacteria, such as NTM organisms. This test can provide probable (presumptive) results within a few hours. It is a valuable tool in helping make decisions about treatment while culture results are pending.
  • Molecular tests for NTM (e.g., nucleic acid amplification test, NAAT) — detect the genetic components of NTM organisms and are often done when the AFB smear is positive or NTM infection is highly suspected. Like AFB smears, molecular tests can provide a presumptive diagnosis, which can aid in the decision of whether to begin treatment before culture results are available. Results of molecular tests are typically available several hours after a sample is collected.
  • AFB cultures to grow the bacteria are set up at the same time as the AFB smears. Though more sensitive than AFB smears, results of cultures may take days to several weeks.
  • Susceptibility testing on the acid-fast bacteria grown in the cultures that are positive will determine the bacteria’s susceptibility or resistance to drugs most commonly used to treat NTM infections.

Once the mycobacteria species has been identified and treatment has begun, AFB smears and cultures are used to monitor the effectiveness of treatment.

Non-Laboratory Tests
X-rays may be ordered to look for changes caused by a mycobacterial infection. NTM infections (and Mycobacterium tuberculosis infections) can cause a number of characteristic findings on x-rays, including cavities (holes) and calcification in organs such as the lungs and kidneys. High-resolution CT imaging may be ordered and has been found to have greater sensitivity for detecting bronchiectasis and cavities than chest x-ray. People with positive findings should undergo further evaluation, which may include bronchoscopy and lung biopsy.

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