Mycobacteriaceae represent a family of bacteria. This family includes several bacterial species, some of which cause human disease, and others which do not. Mycobacterium tuberculosis leads to the onset of tuberculosis in humans. Nontuberculous mycobacteria (NTM) are a species in the mycobacteria group that could precipitate illness, but not tuberculosis (TB).
There are a variety of ways in which NTM are different than TB. TB is a disease that is transmitted from person to person. However, NTM is not. It is not a contagious condition. But precisely how people become infected with NTM has not been specifically determined.
NTM-based disease of the lung describes a family of disorders in which individuals come in contact with mycobacteria. These bacteria exist naturally in soil and water and are not necessarily the cause of disease. They have been classified as nontuberculosis to differentiate them from tuberculosis-causing bacteria, also known as the Mycobacterium tuberculosis (M.tb) complex.
The Mycobacterium avium complex (MAC) is NTM. Although it is related to the tuberculosis family, it is not contagious. It includes more than one bacterium – Mycobacterium avium and Mycobacterium intracellulare. Having MAC can lead to the onset of different diseases of the lungs. The bacteria can infect the pulmonary system, including the lung. Essentially, this infection leads to the development of an inflamed respiratory system.
In one instance, MAC can create several lung-based nodules, often called nodular disease. In another instance, it can cause small hollow areas in the lung’s upper area, which will appear similar to TB. This condition is called upper lobe cavitary disease.
Despite their extensive existence in the environment, the bacteria do not often impact most of the population. It is thought that many who are affected already have an unknown lung defect, or may have a defective immune system. Those at greater risk also may have pulmonary tissue that has been damaged from such illnesses as emphysema, cystic fibrosis, or even previous TB.
Moreover, those who are immunocompromised, for example patients receiving extensive immunosuppressant therapy, including synthetic corticosteroid drugs, stand a strong chance of developing NTM illnesses that can impact other organs in addition to the lungs.
The Mycobacterium tuberculosis complex is the cause of TB. People can become infected with M.tb when they inhale TB-containing droplets of phlegm from another infected person, who may have sneezed or coughed nearby. Although TB is contagious in this manner, it is not as easily spread from one person to another as is a cold. The TB-containing droplets would have to be inhaled over a period of time, such as by college students who live in the same dormitory or among those living under one roof. It would be unusual for a person to become ill with TB after walking near an infected individual who had coughed.
There are two versions of TB, pulmonary TB (PTB) and extrapulmonary TB (EPTB). PTB is the most often occurring condition. EPTB occurs outside of the lungs – areas afflicted include the stomach, lymph nodes, or various bones or joints.
Most often, the body’s immune system rids the body of any TB-causing bacteria, but sometimes latent TB will occur, in which symptoms do not appear, even though the body is infected. It is possible that up to 10% of those with a latent TB infection will develop the ‘active’ illness after several years when their immune system is weakened. On the other hand, a TB infection could also cause symptoms to appear within weeks of infection.
Reviewed by Afsaneh Khetrapal, BSc (Hons)