Tuberculin testing in a tertiary hospital: product variability.

Nine percent of 2,721 hospital employees, previously tuberculin negative, were PPD positive when tested with 5 TU of PPD (Aplisol, Parke-Davis). Seventy percent of the positive reactions were found to be erroneous on retesting with Tubersol (Connaught). The excessive potency of Aplisol led to excessive expenditures of time and money investigating a nonexistent outbreak.