Tuberculin reactivity in Bacillus Calmette-Guérin vaccinated subjects

Abstract

Setting: The Centre for Prevention and Control of Tuberculosis in Barcelona, Spain, where the staff appointed to Training Centers are examined. Aims: To check for tuberculin sensitivity due to Bacillus Calmette-Guérin (BCG) vaccine and ascertain its duration. Method: We compared the results of a tuberculin test (TT) on vaccinated and non-vaccinated subjects. The induration diameter and the time elapsed between BCG vaccination and the TT were determined. Results: Of the 2424 vaccinated subjects, 1489 (61.4%) reacted to TT (≥ 5 mm) and of the 3135 non-vaccinated, 905 (28.9%) reacted, a significant difference. Of 1978 subjects vaccinated between 6 and 14 years of age, 63.3% were TT reactors, compared to 23.9% of the 1948 non-vaccinated. Induration diameters ≥ 15 mm amounted to 11% for vaccinated subjects and 8% for those not vaccinated, a significant difference. The time from vaccination to TT was 13–25 years. Of the 446 subjects vaccinated at birth, 237 were reactors (53.1%); of the 887 non-vaccinated subjects of the same age, 154 (17.4%) reacted. Reactors ≥ 15 mm amounted to 40 (9%) for vaccinated subjects and 46 for non-vaccinated (5.2%), a significant difference. The time elapsed between vaccination and TT was 20–25 years. For 124 vaccinated subjects with a previous negative TT, a second test was positive for 87 (70.2%), and for 257 non-vaccinated it was positive for 64 (24.9%). The difference is due to a booster effect. Conclusions: BCG vaccination at birth and for school age children causes a reactivity to tuberculin which persists for 20 to 25 years. An induration diameter of ≥ 15 mm does not exclude a vaccinal origin. For vaccinated subjects with a previous negative TT, it is necessary to exclude the booster effect.