Simultaneous comparison of reactivity to purified protein derivative RT-23 and Tubersol in health care workers in Vitória, Brazil.

Questions have recently been raised regarding the potency of purified protein derivative (PPD) RT-23, the tuberculin most widely used world-wide for skin testing. We performed simultaneous testing with PPD RT-23 and Tubersol to compare these reagents during a tuberculin survey of 202 adult health care workers at a large teaching hospital in 1997. Individuals were tested with 2 tuberculin units (TU) PPD RT-23 and 5 TU Tubersol using the Mantoux method. Using a 10 mm cut-point for a positive PPD test, 39% of the health care workers were positive when tested with Tubersol and 35% were positive when tested with PPD RT-23. The median PPD size with Tubersol was 4 mm (interquartile range = 0-12 mm) compared to 2 mm (interquartile range = 0-12 mm) with PPD RT-23. PPD skin test reactivity with the two reagents was highly correlated (Spearman's rank coefficient, rho = 0.92; P = 0.01, two tailed). Concordance between the skin test reaction size with the two antigens did not differ based on age, sex or prior BCG vaccination. Mantoux skin test reactivity in health care workers in an area with a high prevalence of tuberculosis was comparable with PPD RT-23 and Tubersol.