Increase in tuberculin skin test converters among health care workers after a change from Tubersol to Aplisol

Background: Comparability of the 2 commercially available tuberculin skin testing (TST) preparations, Aplisol (Parkdale Pharmaceuticals, Inc, Rochester, MI) and Tubersol (Aventis Pasteur, Inc, Swiftwater, PA), remains uncertain, particularly in groups that undergo repeated testing, such as health care workers. Methods: Data from the annual tuberculosis screening program for health care workers at the Kennedy Krieger Institute in Baltimore, Maryland, were analyzed. Conversion rates during 1997-2003 in workers screened with Tubersol (n = 8897 screenings) were compared with 1203 workers who underwent screening with Aplisol in 2004. Repeat testing with Tubersol was examined in those who converted in 2004 with Aplisol. Results: Annual TST conversion rates ranged from 0.3% to 0.9% between 1997 and 2003 using Tubersol. After switching to Aplisol in 2004, the TST conversion rate significantly increased to 2% (P < .001). Among 24 health care workers who were converters with Aplisol in 2004, only 6 of 23 (26%) were converters on repeat testing with Tubersol (1 declined retesting). None of the apparent converters (n = 24) had radiographic evidence of Mycobacterium tuberculosis infection, and there was no epidemiologic evidence of transmission. Reclassification based on Tubersol testing in 2004 resulted in conversion rates comparable with previous years. Conclusion: We conclude that the change from Tubersol to Aplisol resulted in falsely elevated conversion rates. Our results support the guidelines from the Centers for Disease Control and Prevention recommendations that 1 product should be used consistently in populations undergoing periodic testing.