Enhancing of tuberculin allergy by previous tuberculin testing.

A controlled study on the enhancing of tuberculin allergy by one or more earlier tuberculin tests was carried out in a previously untested and unvaccinated population, in an area where the prevalence of non-specific allergy was known to be high. The results have shown that a test with 1 TU of PPD RT 23 in Tween 80 diluent causes subsequent tests to elicit significantly larger reactions. This enhancing effect is more marked among those with initial reactions of 8-13 mm to 1 TU or 10 mm and more to 20 TU. There is practically no enhancement among those whose reactions to 20 TU measure 0-4 mm or even 0-9 mm. Even in the group with reactions of 10 mm and more to 20 TU only some individuals show evidence of enhancement. The enhancing of allergy increases with age.The addition of a 20 TU test increases the enhancement of allergy but mostly among those with reactions of 8-13 mm to 1 TU.The findings suggest that enhancement may be more marked in communities with a high prevalence of non-specific allergy.