The significance of a dual skin test with PPD and PPD-B in humans after BCG vaccination
Landi, S.; Ashley, M.J.
Developments in Biological Standardization 58: 631-636
1986
ISSN/ISBN: 0301-5149 PMID: 3111907 Document Number: 279095
Dual skin tests with tuberculin purified protein derivative (PPD) and with one of the following antigens prepared from mycobacteria other than M. tuberculosis, such as PPD-Y, PPD-G, PPD-B, PPD-F, etc., are performed to establish the frequency of "atypical" mycobacterial infection in a given population. However, most of this work has been done in areas where BCG vaccination was rarely implemented, if at all. The purpose of this study was to assess the significance of a dual skin test using PPD and PPD-B in a population which had been vaccinated with BCG. It was found that in a population with a high level of sensitivity to PPD, median skin reaction 12 mm, only 7% of the subjects tested gave a greater response to PPD-B than to PPD, whereas in a population with a low level of sensitivity to PPD, median skin reactions 3 mm, 36% of the subjects gave a greater response to PPD-B than to PPD. It would appear, therefore, that in a population vaccinated with BCG and with a low level of sensitivity to PPD, a relatively high percentage of positive reactors, those with an induration of 5 mm or more to either PPD or PPD-B, gave a larger skin reaction to PPD-B than to PPD. To avoid erroneous conclusions as to whether or not there is a high frequency of atypical infection in a given population, the authors suggest that the BCG status of those tested with PPD and PPD-B be taken into consideration when interpreting the results of an epidemiological survey that includes an atypical antigen such as PPD-B.