A comparison of purified tuberculins in the south-eastern USA.

Simultaneous tests with 5 TU of the purified tuberculins PPD-S and RT 19-20-21 were given to 1617 schoolchildren in Muscogee County, Ga., and Russell County, Ala., USA. Contrary to findings reported from other places, in this area the qualitative differences between the two antigens were considerable. Low-grade tuberculin sensitivity, presumably nonspecific in nature, was evoked by RT 19-20-21 much more frequently than by PPD-S. Because of this finding, it is obvious that doses of tuberculins which give equivalent responses in one population may not give equivalent responses in other populations whose causes of tuberculin sensitivity may be quite different.