Sensitivity to avian and human PPD in Brisbane School Children

Abstract

Summary 1,065 school' children in Brisbane, Queensland were tested with avian and human PPD standardized by biological assay to give similar potencies relative to one another in their own sensitization. A small dose of each was used in the first instance. The children were divided into two groups according to whether they had previously had a BCG vaccination or not. The larger (1,012 children), non-BCG group gave such a preponderance of larger reactions at 72 hours to the avian PPD as to suggest that any reactions which occurred to the human PPD were, in fact, cross reactions to an infection with an organism antigenically closely related to Myco, avium —probably a Battey Group III organism. Repeating the tests with strong doses of the two PPD's on all children with reactions of less than 5 mm. gave similar results. Only 22·2% of the 1,012 non-yaccinated children gave reactions of less than 5 mm. to either the weak or strong dilutions of the avian PPD. The smaller BCG group of 53 children also showed a preponderance of large reactions to avian PPD but this was much less marked than in the non-BCG group. Comparing these findings with those of a similar investigation in R.A.F. recruits in Britain, it is suggested that the difference in the result of the two investigations arises not only from a difference of tuberculous and anonymous mycobacterial infection between the Brisbane school children in Queensland and the R.A.F. recruits in Britain, but also from the tendency for the sensitivity resulting from the more frequent source of the infection to dominate the other. Dividing adults attending the Brisbane Chest Clinic into bacteriological groups, it was shown that the results of testing them with weak dilutions of human and avian PPD was a fairly sensitive indicator of the degree of infection of the different groups with Myco. tuberculosis and anonymous mycobacteria. This is considered to give further weight to the view that there is a frequent and almost universal infection occurring in the Brisbane school children with anonymous mycobacteria closely related to Myco, avium , cross sensitization to which is causing false positives when testing those children with human PPD.