Tuberculosis tracking: determining the frequency of the booster effect in patients and staff

Two-step tuberculin skin testing, which is recommended to exclude the booster effect as a cause of converting nonreactive skin test responses to reactive responses, can be expensive and logistically challenging. We studied the booster effect in our patients and staff to determine its frequency and to identify factors that might predict its occurrence.

Hospital staff members and long-term care patients were given 2-step Mantoux tests and evaluated prospectively.

Of 619 staff members tested, the initial tuberculin response was reactive in 39 (6.3%). Of the 97 nonreactive staff members who presented for retesting 6 to 30 days later, 6 were now reactive (6.2%; [95% CI, 2.3%-11.8%]). Twelve (13.6%) of eighty-eight patients were tuberculin reactive on their initial skin test. Of the 37 nonreactive patients appropriately administered their second test, 2 (5.4%, [95% CI, 0.7-18.2%]) were tuberculin-reactive. Thirteen percent of tuberculin-reactive staff members and 16% of tuberculin-reactive patients were identified only after their second skin test. Foreign birth (P =.02) was associated with purified protein derivative response boosting in staff members; anemia was associated with boosting in patients (P =.05).

Our results support 2-step skin testing of all new employees and patients who are likely to receive periodic retesting. In our population, age alone is an inadequate criterion for selecting candidates for retesting.