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Skin tests with 0.1 mL of intermediate-strength Mycobacterium tuberculosis purified protein derivative (PPD) and 0.1 mL of Mycobacterium avium sensitin were conducted on 484 healthy subjects from diverse geographic sites. Reactions ofor = 5 mm to one antigen that exceeded the reaction to the other byor = 3 mm were considered M. avium- or PPD-dominant. PPD-dominant reactions were more frequent at sites where routine Bacille Calmette-Guérin immunization is done or where there are high rates of tuberculosis: New Hampshire, 2%; Boston, 7%; Finland, 14%; Trinidad, 26%; and Kenya, 28%. However, rates of M. avium-dominant reactions ranged from 7% to 12% at all sites. Analysis of dominant reactions based on a more stringent 10-mm minimum reaction size showed similar trends. These data suggest that exposure to MAC is similar in developed and developing countries but that broad mycobacterial immunity is greater in developing countries and may contribute to the lower rates of disseminated MAC infections in AIDS in these areas.

To define the genetic diversity among Mycobacterium avium isolates from human immunodeficiency virus-infected patients, specimens were cultured prospectively, and isolates obtained from 14 patients (4 with positive blood, stool, and sputum; 6 with positive blood and stool; 3 with positive blood only; and 1 with positive stool only) were studied. Both serotyping and ribotyping had limited ability to discriminate among isolates from different patients, whereas the distinctive restriction fragment profiles resolved by pulsed-field gel electrophoresis indicated that each patient was infected by a unique strain. Of the 13 bacteremic patients, 2 were bacteremic concurrently with 2 distinct strains. The fact that M. avium isolates from AIDS patients exhibit considerable genetic diversity supports the hypothesis that the infection is acquired from various environmental sources. Further, individual patients are not infrequently bacteremic with > 1 strain simultaneously, which may need to be considered in protocols for the diagnosis and management of M. avium disease.