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We were greatly impressed by the Joint Tuberculosis Committee guidelines on the management of opportunist mycobacterial infections.1 We do, however, wonder why the word “opportunist” has been used to describe the mycobacteria, other than the M tuberculosis complex, that cause human disease. All mycobacteria causing disease, even theM tuberculosis complex, are opportunists. Thus, the latter are often spoken of as causing opportunist disease in HIV positive persons. Since the causative role of these other mycobacteria in human disease was established in the middle of the 20th century, a wide range of collective nouns has been applied to them—atypical, anonymous, MOTT (mycobacteria other than tuberculosis), non-tuberculous, and tuberculoid—as well as opportunist.
The distinguishing feature of almost all mycobacteria other than members of the M tuberculosis complex is that they live freely in the environment. For this reason the expression “environmental mycobacteria” has been in widespread use in recent years. May we suggest that, for uniformity, this expression should be universally adopted.
authors' reply The term “opportunist mycobacteria” was suggested by Marks.1-1 He argued that M tuberculosis, M bovis, and M leprae were obligate pathogens which, if they did get into the environment, could not survive for any significant length of time. The other mycobacteria that cause disease in humans are, as Drs Davies and Grange say, free living environmental organisms and we are all continually exposed to them. However, comparatively few people become infected. Those who do usually have some pre-existing condition which predisposes them to infection—for example, chronic bronchitis and emphysema, bronchiectasis, previous tuberculosis, or some form of immunosuppression. The mycobacteria that are free living in the environment thus need an opportunity to cause disease—hence “opportunist mycobacteria”. It should also be pointed out that not all environmental bacteria cause disease. The nomenclature was discussed both by the Working Party and the full Joint Tuberculosis Committee; in both it was agreed by substantial majorities. This decision is also supported by the current and former directors of the Mycobacterium Reference Unit for England and Wales. We had hoped that the nomenclature argument about this group of mycobacteria could have been laid to rest once and for all after these decisions.