TUBERCULIN TEST CONVERSION DURING REPEATED SKIN TESTING, ASSOCIATED WITH SENSITIVITY TO NONTUBERCULOUS MYCOBACTERIA

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Abstract
Repeating the tuberculin test after a brief interval might result in tuberculin conversion. Healthy volunteers (213) were tested twice, 1 mo. apart, with 5 TU [tuberculin units] of tuberculin purified protein derivative (PPD). Three non-tuberculous Mycobacterium antigens (PPD-G [Gause scotochromogen], PPD-Y [M. kansasii] and PPD-B [M. intracellulare] were applied with the 1st tuberculin test. By widely used criteria, 14 volunteers (6.6%) converted their tuberculin tests from negative to positive on the 2nd testing. Whereas 13 of 103 subjects (12.6%) with non-tuberculous antigen sensitivity converted their tuberculin test to positive, only 1 of 110 subjects (0.9%) with no known prior mycobacterial sensitivity converted to positive (P < 0.005; .chi.2 = 10.05). When retested with 5 TU of tuberculin PPD 6.5 mo after the 2nd test, 9 of 13 converters reverted to negative. Tuberculin conversion may occur when the skin test is repeated at 1 mo. Boosting of cross-reacting mycobacterial sensitivity might have caused a portion of the conversions in this population of young, healthy midwestern volunteers. Sensitivity to M. tuberculosis might be boosted by tuberculin testing. Because the prevalence of sensitization by tuberculous and non-tuberculous mycobacteria probably varies in different populations, the significance of tuberculin conversion probably varies with the population being tested.