Two-step tuberculin skin test in nurse students

Abstract

The tuberculin skin test (TST) was conducted in 243 nurse students (19.4 +/- 1.3 years old). The second TST were carried out in 240 students who did not show blister or necrosis in the first TST. The size of erythema was 16.5 +/- 9.4 mm in the first TST (T1) and 24.3 +/- 15.6 mm in the second TST (T2). The negative reactors, whose size of erythema was below 10 mm, were decreased from 53 to 25, whereas, the strong reactors, whose size of erythema was more than 30 mm, were increased from 11 to 71. The difference of the size of erythema (T2-T1) was 9.7 +/- 11.9 mm in the group I (190 students) who received the latest TST in junior high school, whereas, that was 0.5 +/- 9.2 mm in the group II (50 students) who received the latest TST 14 months before this study. T2-T1 in the group I was weakly correlated with T1. Twenty-four negative reactors received BCG vaccination, and 23 of them converted to positive. Seventy-one strong reactors were checked by chest X-ray, and none showed the findings of tuberculosis, and required the administration of anti-TB drug. The two-step TST is an essential means to know the baseline reactivity to TST, and to distinguish newly infected tuberculosis from booster phenomenon.