Reviewed by Shannon H. Kasperbauer, MD
Unlike tuberculosis (TB), which is spread from person to person, nontuberculous mycobacteria (NTM) infections are not considered contagious.

How and why people become infected with NTM is not clear. The nontuberculous mycobacteria (NTM) causes are still under investigation.

Although the bacteria is found easily in water and soil, they do not affect most people. Doctors believe that some people who become infected have an unknown defect in their lung structure or function or in their immune systems. People who have damaged lung tissue from diseases such as emphysema, bronchiectasis, adult cystic fibrosis or previous infection appear to be at greater risk for developing a NTM infection. People who have a suppressed immune system, such as those who receive strong immunosuppressant medications like prednisone or newer immunosuppressants like TNF inhibitors, have a greater risk of developing an NTM infection. The infection may affect all organs of the body, not just the lungs. People with AIDS may also develop NTM infections.

There are studies that have shown a higher burden of infection in states with higher water vapor content. There is also supportive evidence for people acquiring the infection from their local water supply. In considering an apparent increase in the number of NTM lung disease seen over the past 25 years, it has been noted by researchers in the field, such as Dr. Pace in Boulder and Dr. Falkinham in Virginia, that NTM are commonly recovered from home water systems.

There are several theories regarding the increasing incidence of infection. One relates to showering rather than bathing in a tub. Showering in a closed stall exposes the user to a higher aerosol concentration of NTM. In addition, to save energy, water heaters have lower temperatures now, which could allow more NTM growth in the water. The materials used in homes may be more supportive for biofilm growth, which is a hospitable environment for these organisms to grow. Water filters are now used in most homes. They remove the organic compounds that make our water taste bad, but they do not filter out mycobacteria. In fact, the filters themselves may serve as a breeding ground for organisms and allow for higher concentrations of mycobacteria compared to unfiltered water. Finally, there are data to indicate that aspiration of water, either through swallowing or gastroesophageal reflux, is a way that mycobacteria gain access to the lungs to cause disease.

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