Nontuberculous Mycobacteria Week

General Information

Nontuberculous Mycobacteria Week

What are NTM?

NTM is the abbreviation for 'nontuberculous mycobacteria', the microbes that cause 'NTM infections' or 'NTM disease'. (These two terms are often used to denote the same thing.) A special characteristic of mycobacteria is that their cell walls are very waxy, with lots of lipids. The most virulent mycobacteria are Mycobacterium tuberculosis, the cause of tuberculosis (TB), and M. leprae, the cause of leprosy. The remaining 200 or so species of mycobacteria are considered 'nontuberculous' to distinguish them from M. tuberculosis. NTM live in water, soil, and other niches of the environment. They are often called 'opportunistic pathogens', meaning that they do not usually harm healthy persons, but only those with weakened lung defenses or immune deficiencies.  In contrast, M. tuberculosis is an obligate pathogen, meaning that it must cause disease to be transmitted from one person to another.

There are many species of NTM that can cause disease, but the ones causing the most human disease are those in the Mycobacterium avium complex (MAC) and those in the Mycobacterium abscessus group. 

Who develops infections with NTM?

Persons with 'structural lung disease' are at risk for acquiring NTM infections.  'Structural lung disease' refers to conditions where the normal anatomy of the lung is altered deleteriously, most commonly with inflammation of the airways, or bronchial tubes. The most common structural lung diseases associated with NTM lung infections are bronchiectasis and chronic obstructive pulmonary disease (COPD). 

In children, the most common patients affected are those with cystic fibrosis (CF).  CF alters the fluid that lines the bronchial tubes, resulting in thick tenacious secretions that are usually difficult to clear.  In adults, bronchiectasis also occurs for a variety of reasons, including milder variants of CF than those that typically begin in early childhood.  Unfortunately, most bronchiectasis in adults is considered 'idiopathic', meaning that we do not understand the cause of the disease.

How is NTM disease diagnosed?

Most NTM disease affects the lungs.  Pulmonary NTM disease is diagnosed based on (1) symptoms, (2) imaging tests and (3) microbiological confirmation. Typical symptoms of pulmonary NTM disease are cough and fatigue but fevers, weight loss and night sweats may also occur. The latter systemic symptoms are more common in disseminated infections, which may also present with a variety of other symptoms depending on what organs are involved. 

How is NTM disease treated?

Not all NTM disease needs to be treated. Very mild disease, e.g., nodular MAC, with very mild symptoms might reasonably be managed only by focusing on clearing the airways of secretions.  We recommend airway clearance devices for most of our pulmonary NTM patients.  Other airway clearance measures are inhaled hypertonic saline, aerobic exercise, and percussion vests. 

The decision to treat with drugs is usually made by discussions between the physician and the patient and involves weighing the benefits and risks of treatment versus observation.  NTM tend to become resistant to drugs if only one is used, and some of the antimycobacterial are not as effective as we would like.  Thus, most treatment regimens involved multiple drugs.  The most common treatment for pulmonary MAC is azithromycin, ethambutol, and rifampin.  For mild disease, these can be administered on only three days of the week.  For more typical disease or to help patients remember more easily, they are administered daily.  We usually treat for one year beyond the first negative culture (if sputum is available), which is usually a duration of at least 18 months. For patients who have cavities in the lung or who have severe symptoms, intravenous medication, usually amikacin, may be needed for weeks to months if tolerated.

In addition to medical treatment, adjunctive surgical treatment is sometimes recommended. This can be a very difficult decision that I recommend only be done at centers with expertise.  The most common indication for surgery is that medical treatment alone is not curative and there is a well-defined area of lung destruction, e.g., a cavity or severe bronchiectasis, that can be removed.  These may be sites where drugs do not achieve adequate concentrations and where the bacteria continue to grow. 

What should be monitored? 

Sputa specimens are obtained periodically to monitor the response to therapy, with the hopeful goal of becoming  negative, i.e., not growing the NTM.  We also follow microscopy of 'smears' of the NTM (a.k.a. 'acid-fast bacilli (AFB) for their characteristics in picking up special stains). AFB smears reflect the quantity of bacteria in the sputum.  It takes about 5-10,000 bacilli in a milliliter of sputum to see AFB under the microscope, so if specimens become AFB-smear negative but remain culture-positive, it means that the concentration of bacteria has become very low.

In patients who do not produce sputum, the 'C-reactive protein' is a blood test that is a non-specific marker of inflammation that can be helpful to follow as a treatment outcome.

What is the Prognosis? 

The response to treatment can vary greatly and depends on the underlying disease(s) as well as the NTM species and amount of lung damage.  Generally, about 75% of patients with nodular bronchiectasis and pulmonary MAC that is not far advanced may be expected to obtain a microbiological cure.  Unfortunately, for those with COPD, especially with cavitary disease, microbiological cure may only be 50% of less. 

How do we prevent re-infection?

Many patients are naturally curious about why and how they acquired their NTM infections, and given the risk of re-infection, they want to know how to prevent it. The only thing certain about this is uncertainty of the medical community.  There have been intense research efforts to identify NTM in home and municipal water supplies, showers, pools etc.  There have been some very interesting but often mixed results that have resulted in controversy and debate. I think that it is safe to say that most of us in this field advise patients with bronchiectasis and NTM disease to definitely avoid hot tubs, given the numerous case reports of NTM contamination. Similarly, there are advocates of extreme measures to minimize GERD and possible pulmonary aspiration, but we are lacking scientific data to support definitive guidelines. My personal recommendation is to stay active, well-nourished, and to work on airway clearance measures if possible.  Unfortunately, there are no vaccines or prophylactic drugs that have been shown to be helpful.  However, we are entering an exciting era with unprecedented interest in NTM infections in the general community and by pharmaceutical companies. This offers great hope for accelerated progress for the future care of NTM patients.

Four Facts About Nontuberculous Mycobacteria (NTM)

  1. Mycobacteria are naturally occurring environmental organisms found widely in both water and soil and can cause significant respiratory damage.

  2. People with underlying lung disorders such as COPD, Alpha-1 Antitrypsin ‎Deficiency, Cystic Fibrosis, Bronchiectasis and others, are at greater risk for NTM infection

  3. NTM can be difficult to diagnose and is often mistaken for tuberculosis. Delay in treatment can result in additional damage to the respiratory system.

  4. The exact number of pulmonary NTM patients in the United States is not known. Past studies estimated the number between 50-90 thousand people at any given time, however new data shows diagnosis is increasing at about 8% per year.