A clinical comparison between Mycobacterium avium and Mycobacterium intracellulare infections

Susceptibility, clinical features, and response to treatment were compared between 29 cases of Mycobacterium avium infection and 43 cases of Mycobacterium intracellulare infection detected in the Nagasaki (Japan) area and identified by a DNA probe method. In vitro susceptibility of two species to antituberculous agents was determined by a microdilution method, and M avium was more resistant to enviomycin at 25 mg/L than M intracellulare, while M intracellulare was more resistant to isoniazid at 5 mg/L and to cycloserine at 20 mg/L. No significant difference was found between infections caused by two species as to background factors, laboratory data, clinical symptoms, and chest radiographic findings at the onset of the disease. Approximately 70 percent of the patients in each group had underlying diseases; among them, pulmonary tuberculosis was the most common. Negative conversion of bacilli during the 6-month treatment was seen in 17 of 29 patients (59 percent) with M avium infection and in 21 of 43 patients (49 percent) with M intracellulare infection. Bacilli-negative conversion was slightly faster in the former than in the latter. However, these differences were statistically not significant. In conclusion, most M avium-intracellulare complex organisms are clearly identified as M avium or M intracellulare by the DNA probe method, and there was no significant difference in clinical features and response to treatment between infections caused by the two species.