Tuberculin reactivity in Bacillus Calmette-Guérin vaccinated subjects

The Centre for Prevention and Control of Tuberculosis in Barcelona, Spain, where the staff appointed to Training Centers are examined.

To check for tuberculin sensitivity due to Bacillus Calmette-Guérin (BCG) vaccine and ascertain its duration.

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.

Of the 2424 vaccinated subjects, 1489 (61.4%) reacted to TT (> or = 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 > or = 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 > or = 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.

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 > or = 15 mm does not exclude a vaccinal origin. For vaccinated subjects with a previous negative TT, it is necessary to exclude the booster effect.