Sensitivity to avian sensitin of tuberculin reactors in Belgium

It was proposed that a study should be made on the specificity of the reactions of 1068 subjects reacting "weakly to moderately" to an intradermal test with 2 units of PPD RT23; 43% were classified as "positives" (greater than or equal to 10 mm) and Palmer type IV indurations or merely erythema were seen in 81%. Three months later, the same people were retested, this time with 2 units of PPD RT23 and, simultaneously, with 0.1 mcg of avian sensitin: 23% of all reactors (13% of all "positives", but none with a Palmer type I of II induration) had completely lost their sensitivity to RT23. Of the 1068 original reactors, 87% reacted to avian sensitin and 69% did so with a reaction greater than or equal to to human RT23. According to the results of this double test, and depending on the strictness of the comparative criterion, 69% to 84% of the original reactors (65% to 78% of the "positives") would be classified as non-specifically infected. There was a high degree of agreement between an induration greater than or equal to 10 mm to PPD RT23 in the second test and classification as specific infection, based on a comparative criterion.