Nontuberculous mycobacteria

Nontuberculous mycobacteria (NTM), also known as environmental mycobacteria, atypical mycobacteria and mycobacteria other than tuberculosis (MOTT), are mycobacteria which do not cause tuberculosis or leprosy (also known as Hansen's disease). NTM do cause pulmonary diseases that resemble tuberculosis.Mycobacteriosis is any of these illnesses, usually meant to exclude tuberculosis. They occur in many animals, including humans.

Mycobacteria are a family of small, rod-shaped bacilli that can be classified into 3 main groups for the purpose of diagnosis and treatment:

In 1959, botanist Ernest Runyon put these human disease-associated bacteria into four groups (Runyon classification):

The number of identified and cataloged NTM species has been increasing rapidly, from about 50 in 1997 to over 125 by January 2007. The surge is mainly due to improved isolation and identification technique.

However, even with these new techniques, the Runyon classification is still sometimes used to organize the mycobacteria into categories.

NTM are widely distributed in the environment, particularly in wet soil, marshland, streams, rivers and estuaries. Different species of NTM prefer different types of environment. Human disease is believed to be acquired from environmental exposures, and unlike tuberculosis and leprosy, there has been no evidence of animal-to-human or human-to-human transmission of NTM, hence the alternative label "environmental bacteria".

NTM diseases have been seen in most industrialized countries, where incidence rates vary from 1.0 to 1.8 cases per 100,000 persons. Recent studies, including one done in Ontario, Canada, suggest that incidence is much higher. Pulmonary NTM is estimated by some experts in the field to be at least ten times more common than TB in the U.S., with at least 150,000 cases per year.

Most NTM disease cases involve the species known as Mycobacterium avium complex or MAC for short, M. abscessus, M. fortuitum and M. kansasii. M. abscessus is being seen with increasing frequency and is particularly difficult to treat.

Mayo Clinic researchers found a three-fold increased incidence of cutaneous NTM infection between 1980 and 2009 in a population-based study of residents of Olmsted County, Minnesota. The most common species were M. marinum, accounting for 45% of cases and M. chelonae and M. abscessus, together accounting for 32% of patients.M. chelonae infection outbreaks, as a consequence of tattooing with infected ink, have been reported in the United Kingdom and the United States.

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