Status of mycobacterial infections of the lungs.

Tuberculosis continues to constitute the principal mycobacterial pulmonary disease. Control measures are known and their effectiveness limited mainly by social and economic factors. Other mycobacterial diseases are not so readily controlled owing to incomplete knowledge of epidemiology, pathogenesis and treatment. The Runyon classification given in table I developed as cultural character­ istics of the “atypical” mycobacteria became known. Groups I and III generally represent pathogenic (significant) species while Groups II and IV are generally saprophytes (not significant) or opportunistic. The occurrence of clinical dis­ ease due to atypical mycobacteria is variously estimated as 0.1 to 10 percent of that of tuberculosis. The term mycobacteriosis is commonly applied. The mode of acquisition and transmission of the organisms is not known but manto-man transmission has not been proved. Atypical mycobacteria generally grow less well on cultures than M. tuberculosis. When acid-fast bacilli are found on smears, cultures should be observed for a longer period of time than is usual for M. tuberculosis. Most commonly observed, clinically, are M. kansasii ( Group I ) and M. intracellulare (Group III) . Mycobacteriosis is more common in males and in ad­ vancing age. Other pulmonary disease is commonly present and it is often difficult to distinguish primary from complicating disease. Diagnosis of tuber­ culosis is commonly made and revised when atypical mycobacteria appear on culture. Clinically, the disease is indolent, tends to wax and wane and responds variably to drugs. Thin-walled cavities give evidence of the breakdown of lung tissue. Disability occurs with some frequency in older males. Recent experience in 25 cases of unquestioned significance showed 14 in Group I, 2 in Group II and 9 in Group III. By contrast, a group of 30 persons with only bacteriological evidence of mycobacterial infection showed 4 in Group I, 10 in Group II, 10 in Group III and 6 in Group IV. The larger pro­ portion of Group II and IV infections indicated that few among these 30 cases were clinically significant. Treatment of people with Group I infections is usually similar to that of tuberculosis but ethambutol is especially recommended. Group III bacilli respond poorly to standard drugs and, if progressive, a combination of 4 or 5 anti-mycobacterial agents may be employed. Rifampin is proving useful in