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Interpretation of Tuberculin Reactions in Persons with a History of BCG Vaccination
Many foreign countries still use BCG as part of their TB control programs, especially for infants. In persons vaccinated with BCG, sensitivity to tuberculin is highly variable, depending upon the strain of BCG used and the group vaccinated. The presence or size of a postvaccination tuberculin skin-test reaction does not predict whether BCG will provide any protection against TB disease. Furthermore, the size of a tuberculin skin-test reaction in a BCG-vaccinated person is not a factor in determining whether the reaction is caused by M. tuberculosis infection or by the prior BCG vaccination.
Tuberculin skin testing is not contraindicated for persons who have been vaccinated with BCG, and the skin-test results of such persons are used to support or exclude the diagnosis of M. tuberculosis infection. The booster phenomenon may occur among persons who have had a prior BCG vaccination (see Two-Step Testing). A diagnosis of M. tuberculosis infection and the use of treatment for infection should be considered for any BCG-vaccinated person who has a tuberculin skin-test reaction of ³10 mm of induration, especially if any of the following circumstances are present:
Treatment for infection should be considered for BCG-vaccinated persons who are infected with HIV and who are at risk for M. tuberculosis infection if they have a tuberculin skin-test reaction of ³5 mm induration. Because HIV-infected persons may be anergic (i.e., may not react to tuberculin because of immunosuppression), isoniazid treatment for infection should be considered for these persons if they have a history of contact with another person who has infectious TB, regardless of the fact that they may be nonreactive to tuberculin.