Two-Stage Tuberculin Testing in a Prison Population

Abstract

In the New Mexico Corrections Department, mass screening of male inmates revealed a purified protein derivative of tuberculin (PPD) conversion rate of 3.9 percent and led to the institution of two-stage skin testing of all new inmates. This policy change resulted in a drop of the annual conversion rate to O.9 percent. An analysis of the two-stage testing program showed that of 518 subjects classified as PPD positive, 121 were so classified on the basis of a documented history of a prior positive test, and 397 underwent the two-stage protocol. Of these, 273 (69%) had a significant reaction to the first test. The remaining 124 (31%) required the booster effect of the first test and had significant reactions only to the second test. Two-stage testing is recommended for new inmates of long-term correctional facilities, in order to establish accurate baseline information and to avoid the trap of false converter rates.