Nontuberculous mycobacteria (NTM) are bacteria that grow and survive naturally in water and in dirt. These bacteria have been classified as nontuberculosis to distinguish them from tuberculosis-causing bacteria, also known as the Mycobacterium tuberculosis complex.
As a family of bacteria, NTM include more than 150 different species. Many of these often do not lead to the onset of illness in humans, however, in some instances, those with poor immune defenses may become ill. Those who fall ill find that the bacteria had infected tissues of the lung and the airway, and their condition probably will lead to a progressive pulmonary infection.
A number of symptoms can present when a person is infected with NTM, including:
- A constant cough.
- Spitting up bloody mucus.
- Loss of weight.
Not every individual will experience the exact same signs and symptoms of NTM. Scientists do not yet know why the symptoms can vary from person to person. An individual may present with symptoms that appear similar to other diseases of the lung and respiratory systems. A cough (sometimes bloody), exhaustion, an inability to breathe properly, fever and sweating, and a loss of both weight and the desire to eat may appear in individuals. Respiratory illnesses may reoccur in some people, with damage to the lungs occurring over time, causing their function to be impaired. Generally, chronic lung infections are the most common complication of NTM.
There are several risk factors for NTM-based lung conditions. First, it is usually older adults who experience NTM disease. Underlying pulmonary conditions, such as chronic obstructive pulmonary disease, including chronic bronchitis and emphysema, may cause NTM disease. Tall, thin Caucasian females are thought to have a greater chance of contracting NTM disease of the lung. These individuals also have breastbone irregularities, bent spines, and heart conditions.
The potential for NTM disease increases if individuals have poor immune systems – this may result from rheumatoid arthritis, which can weaken the immune system. Some therapeutics, including steroidal drugs, also can put the immune system at risk and increase the potential for NTM disease. Diseases of the esophagus, including gastroesophageal reflux disease, can lead to NTM conditions of the lung. If the bacteria are living in swimming pools or in soil, then exposure to the microbes can increase the chance for infection, especially in the immunocompromised.
Diagnosis of NTM conditions will require performing lab tests, chest x-ray imaging, a CAT scan, a physical examination, and taking a person’s medical history. In addition, cultures of the airway or of saliva and mucus may be taken to see if they test positive for NTM. A lung biopsy also may be considered.
X-ray findings that indicate the existence of NTM conditions will show netlike chest radiographic patterns; the existence of several nodules; bronchiectasis with an enlargement of parts of the airways of the lung; same lobe bronchiectasis and nodules; and opaque air spaces, caused by the filling of alveoli with blood, pus, or other liquid.
NTM diseases are usually classified as fast or slow-growing. Some can grow in culture within seven days. The slower growing microbes may take up to one month to grow in solid medium. After growth is observed, researchers can use nucleic acid techniques to determine the specific type of bacteria present.
Yet making a diagnosis may not be straightforward - it is complicated because the clinician will be looking for symptoms that vary between individuals. Other conditions also must be ruled out, including tuberculosis.
Reviewed by Afsaneh Khetrapal, BSc (Hons)