Absence of the booster phenomenon in serial tuberculin skin testing

The Center for Disease has recently recommended that tuberculin skin testing of new hospital employees be done in two steps because of the so-called "booster phenomenon." To assess the feasibility of the two-step method in our hospital, we performed a pilot study using this method on all our new hospital employees during a 6-month period. From July 1, 1980, to December 31, 1980, all newly hired employees of the Strong Memorial Hospital were given a two-step tuberculin skin test as part of their preemployment health evaluation. During this time, 571 new employees were tested, 416 (73%) of whom completed both steps. The mean age of the 416 employees was 26 yr. Fourteen of 448 employees (3.1%) had positive reactions on the first test. None of the 416 employees had positive reactions on the second test. Additional visits for skin test administration, costs of informational materials, administrative expenses, and supplies added approximately $2,600 to the costs of our tuberculin skin testing program during the study period. The absence of the booster phenomenon in our employee population may be due to (1) the relatively young age of our hospital employee population who may be less likely to have remote infection with Mycobacterium tuberculosis and/or (2) the relatively uncommon occurrence of nontuberculous mycobacterial infection in our area of the country. Depending on the age of employees of an institution and its geographic location, the two-step method may not detect any additional reactors. We recommend that hospitals contemplating adoption of this method first perform a similar pilot study in order to assess the frequency of the booster phenomenon in their employee populations.