The booster phenomenon in two-step tuberculin testing of employees in a community hospital

Abstract

A study was made to clarify to what degree the booster phenomenon was present when the employees in a community hospital in Japan received two-step tuberculin testing (PPD). Of the seventy-five employees, most of all BCG-vaccinated subjects, twenty-three showed strongly positive of more than 30 mm of induration at the first test (PPD/T1), and the remaining fifty-two subjects received a second (PPD/T2) after 2 weeks. The second PPD showed a marked increase in reactivity, sixteen subjects newly became strongly positive and six of eight who were initially PPD negative (< 10 mm) were converted positive, and the mean reaction size changed from 14.7 +/- 5.6 mm (PPD/T1) to 31.5 +/- 15.5 mm (PPD/T2). The degree of boosting, measured by the change in millimeters induration size between PPD/T1 and PPD/T2 (PPD/T2-PPD/T1), was correlated with neither the size of PPD/T1 nor the age of the study participants, and was not associated with the difference of the position in the hospital. Thus, we could not explain the factor why such a marked boosting was observed in this study. However, these results indicated that the two-step tuberculin testing is an essential means of distinguishing new tuberculous infection from booster phenomenon. We agree with the current recommendation for routine two-step testing of new employees in the hospital.