SINGLE + MULTIPLE INFECTIONS WITH TYPICAL + ATYPICAL MYCOBACTERIA

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Abstract
A group of 246 medical students was tested with 5 TU doses of PPD made from typical and atypical mycobacteria. Approximately 14 per cent of the students reacted positively to PPD-S, PPD-Y, and PPD-F. Almost twice as many (24.3 per cent) reacted to PPD-B, and three times as many (51.8 per cent) to PPD-Scot. Eighty student nurses, who were approximately five years younger than the medical students, gave about one-half as many positive reactions with each PPD antigen. With single infections in guinea pigs, the human, photochromogen, and M. fortuitum organisms gave only small cross-sensitivity to the other antigens. In contrast, Battey and avain sensitization gave relatively large cross-reactions to scotochromogen PPD. Scotochromogen sensitization gave relatively large cross-reactions to avian and Battey PPD. Double infections in guinea pigs with human and photochromogen organisms showed a mutual reinforcement of the reaction to PPD-S and PPD-Y; therefore, it would have been impossible to say which was primary, although there was much less cross-reaction to the other antigens. Single infections with typical and atypical mycobacteria apparently can be detected by a series of 5 TU tests. With some combinations, double infections can be identified; but, with other combinations, the double infections cannot be distinguished from triple infections. For dependable results duplicate tests should be performed with each specific PPD to eliminate false results from mechanical errors in skin testing.