Taxonomic differences between Mycobacterium avium and Mycobacterium intracellulare elucidated in man by skin tests with three new tuberculins.

New tuberculins called Aviumins A, B and C prepared from M. avium, its proposed subspecies M. avium brunense and M. intracellulare respectively have been skin tested on school children in six countries as a part of larger studies. The results show that the reagents are recognised separately in most cases by the human immune system. Although there is some significant interdependence in sensitization to these reagents, the frequency of meeting the organisms must be very high since 33% of children with a mean age of 8 years produced positive responses to Aviumin A and 40% of them produced positive responses to Aviumin C. Besides age, other factors influencing responsiveness were BCG and sex. Both Aviumin A and B sensitization were significantly increased in the presence of a BCG scar, whereas Aviumin C tended to show the reverse trend. Sex had little effect on responses to Aviumins A and B but had an unexpected significant effect on Aviumin C, with more boys than girls producing positive reactions to it.