Correlating Two-Step Tuberculin Skin Test Positivity Rates in New Employees with Mycobacterium tuberculosis Disease in Veterans Health Administration Medical Centers Nationwide

Abstract

BACKGROUND/OBJECTIVES: Healthcare facilities remain a potential risk environment where transmission of Mycobacterium tuberculosis disease (TB) will occur. As Mtb cases decrease in the United States, more emphasis is being placed on latent tuberculosis infection. The Veterans Health Administration (VHA) is a national healthcare system with over 4 million patients seen during the last year, for which approximately 600,000 inpatient admissions occurred and over 35 million outpatient visits. VHA employs over 200,000 individuals, has countless volunteers, and provides an educational venue for a significant proportion of healthcare trainees nationwide. One means to identify latent tuberculosis infection and prevent potential for transmission is by identifying employee/volunteers who are infected at initiation of employment and ensuring preventive therapy if appropriate, including two-step Tuberculin skin testing (TST) for certain persons. The VHA provides an opportunity to assess correlation of two-step TST, preemployment positivity, and occurrence of TB disease in patients. METHODS: Through an electronic, annual census instrument, the VHA has followed TB among patients since federal fiscal year (FY) 1991 and varied components of TST programs since 1993. RESULTS: In the VHA, between FY 1992 and FY 2001, TB, multidrug-resistant (MDR) TB, HIV-associated TB, and MDR-TB with HIV have all significantly decreased over time (p<0.0004 for all). Total TB cases fell from 781 in FY 1992 to 306 in FY 2001. Nationally, for FYs 2000 and 2001, the number of new VHA employees/volunteers was reported at approximately 37,500 and approximately 43,500, of whom approximately 32,000 and approximately 35,000, respectively, met criteria for pre-employment TSTing. During this time period, the number of two-step TSTing of new employees/volunteers was reported at 13,465 and 14,245, respectively; positivity for the second step was 163 (1.21%) and 200 (1.40%), respectively. Correlation coefficients examining the general association between the number of TB cases in patients and both number of positive two-step TSTs and percent of positive two-step TSTs among employees indicates a positive relationship with r=0.37 (p=0.0364) and r=0.19 (p=0.0061), respectively (i.e., as the number of TB cases increases so do the number or percent of positive two-step TSTs). CONCLUSIONS: These data suggest an association between cases of TB among patients treated within healthcare facilities and two-step TST positivity among employees/volunteers during pre-employment examination. This may represent community background rates of positivity on two-step TSTing.