It is not necessary to take medicine---回複：回複：辦綠卡，我和

Americans usually do not get BCG (the vaccine against TB) and they normally do not have immunity to TB. If they have positive result of PPD test, it may indicate they have infected by the bacterium which induces TB. The PPD test, A.K.A TB test which is not a good name, actually checks the immunity against TB. The explanation of PPD positive result should be different among the different populations.