Search

The aim of this study was to evaluate the tuberculin skin test in individuals vaccinated with bacillus Calmette-Guérin (BCG) using 2 IU of RT-23. One hundred ninety-six individuals aged 22-40 years-old who had been vaccinated with BCG between 1965 and 1974 were enrolled along with 375 non-vaccinated individuals of the same age and with similar level of risk of infection. The positive predictive value of the test was assessed for three levels of response as indicated by areas of thickening in three diameters: 5, 10 and 15 mm. Vaccinated individuals with negative results were given a second skin test 7 days later to detect a booster effect. Positive diameters 5 mm were observed in 66% of the vaccinated individuals and 24% of the non-vaccinated subjects. Positive diameters 10 mm were observed in 51% of the vaccinated individuals and 19% of the non vaccinated ones. Positive diameters 15 mm were observed in 29% of the vaccinated subjects and in 13% of the non vaccinated ones. The differences were significant for all diameters. The positive predictive value of the test was 36.4% for a diameter 5 mm, 37.6% for diameter 10 mm and 44.8% for diameter 15 mm. The booster effect was detected in 25.8% of the vaccinated individuals who had tested negative at first. In vaccinated individuals, no guidelines can be established to guarantee that a positive reaction is due to infection by Mycobacterium tuberculosis infection, although the likelihood of infection (increased positive predictive value) increases with diameter. It is also impossible to fix a time limit. A second skin test is needed to detect a booster effect in all vaccinated individuals whose first test is negative.

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 (> 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., 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 > 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.