Variation in Sensitivity to Tuberculin1,2

Approximately 25,000 persons, 90 per cent of whom were school children, were tested with tuberculin each year between 1965 and 1969, using the Heaf tine test. Persons were retested regardless of the previous tuberculin reaction. Considerable variation in individual tuberculin sensitivity was observed from one year to the next, and variation in sensitivity was the rule rather than the exception. The changes in degree of sensitivity followed a definite pattern. These changes were gradual from one degree of reactivity to the next higher or lower degree and were seldom abrupt. The evidence suggested that most small reactions are specific in persons who are in the process of acquiring or losing a greater degree of sensitivity.