Does giving BCG prevent the use of the tuberculin test in determining the presence of infection with M. tuberculosis?
This is another area of controversy . BCG converts the tuberculin test from negative to positive. Workers are split as to whether it is possible to tell the difference between a positive test due to BCG alone and a positive test due to infection with M.tuberculosis whether the individual has had previous BCG or not. In the UK we believe it is possible to do this on the basis of the degree of positivity.(6) The USA do not use BCG partly for the reason that they do not believe it is possible to make the distinction. The importance of this is the decision to give preventive therapy for Latent Tuberculosis Infection (LTBI). The USA has relied on prevention by determining whether infection (without disease) is present on the basis of regular tuberculin testing for those at risk of infection such as health workers. BCG is not given as it is believed to interfere with the interpretation of the tuberculin test. Other countries, such as the UK, do give BCG but in cases where infection has occur
