Comparison of a New ESAT-6/ CFP-10 Peptide-Based Gamma Interferon Assay to Tuberculin Skin Test for Tuberculosis Screening in a Moderate Risk Population Esmaeil Porsa, MD, MPH; Lee Cheng, MD, MS; Edward A. Graviss, PhD, MPH THE JOINT PRIMARY CARE FELLOWSHIP Introduction  Tuberculosis (TB) transmission in the correctional facilities represents a significant public health problem.  Screening for persons at risk for latent tuberculosis infection (LTBI) is the first and an essential step in a comprehensive approach to TB control and elimination.  Despite various limitations including poor specificity, the Mantoux tuberculin skin test (TST), remains the gold standard for LTBI screening.  Recently developed in vitro whole blood gamma interferon assay (QuantiFERON ® -TB-GOLD (QFT-G)) is reported to have several potential advantages for LTBI screening: The need for only a one-time patient contact. Increased specificity. Elimination of subjectivity in administering the test or reading the result. Availability of test results within 24 hours. Simultaneous measurement of reactivity to multiple antigens including a control antigen and a non- tuberculous mycobacterium antigen. Methods  Study design: Cross-sectional screening study.  Study Population: Adult inmates recently incarcerated at the Harris County Jail (HCJ) in Houston, Texas.  Exclusion criteria: Immunosupression (HIV/ AIDS, organ transplants, Diabetes, Chronic renal failure, cancer, treatment with immuno-supressive drugs (corticosteroids, etc.), and history of prior positive TST or TB disease.  Sample Size: 539 inmates were enrolled. 59 inmates were excluded. 50 inmates were lost to follow-up. 32 inmates had indeterminate ELISA results. Data from 409 subjects were used for the statistical analysis.  Screening Tests:  QFT-G: This test measures the amount of IFN-gamma secreted by M. tuberculosis (MTB) sensitized T-lymphocytes in response to stimulation by the highly MTB specific antigens “CFP-10” and “ESAT-6” (Cellestis. Inc.)  TST: This test detects a delayed hypersensitivity reaction which consists of an induration at the site of intra-dermal injection of PPD caused by infiltration of sensitized T-lymphocytes.  Statistical analysis: Kappa Correlation and C oncordance (overall % agreement) between the results of TST and QFT-G was assessed. Multivariable logistic regression was used to asses demographic and risk factors that may affect the concordance between these tests. All analyses were performed by using the SAS 8.2 (SAS Institute, Inc. Cary, NC). Objectives  To evaluate the utility of the QFT-G assay in detecting LTBI and to compare its diagnostic performance with that of TST.  To test the Kappa correlation and concordance between TST and QFT-G.  Identifying factors associated with decreased concordance between the test results. Summary  The Kappa statistic showed low agreements between TST and QFT-G. These lower values of Kappa may be due to low prevalence situation.  Reactivity of the new QFT-G assay is unaffected by prior BCG vaccination or serial tuberculin skin tests but may be diminished in African Americans.  Future longitudinal studies are needed to assess the sensitivity and specificity of this new assay in detecting LTBI. Hypothesis QFT-G will improve the accuracy and efficiency of TB screening in correctional facilities due to its increased specificity. Results LTBI prevalence was 9.0% and 5.4% by TST and QFT-G assay. Overall agreement between test results was 90% (κ=0.25). Positive TST results were significantly associated with increased age, African American ethnicity, foreign birth, and prior incarceration. Positive QFT-G assay results were significantly associated with African- American ethnicity. Factors associated with statistically significant discordance between TST and QFT-G assay results were African American ethnicity, foreign-birth, and prior incarceration. Supported by Health Resources and Services Administration (HRSA) Bureau of Health Professions Grant D14 HP00045 and National Institute of Diabetes and Digestive and Kidney Diseases (NIDDKD) T35 DK TST/ QFT-G Assay Concordance Variablesn (%)Crude OR (95% CI)Adjusted OR (95% CI) Age409 (100)0.98 ( )0.97 ( ) Gender Female114 (27.9)1.00 Male295 (72.1)0.93 ( )0.85 ( ) Ethnicity Caucasian145 (35.5)1.00 Afro-American173 (42.3)0.30 ( ) a 0.29 ( ) a Hispanic91 (22.2)0.26 ( ) a 0.34 ( ) Birth Country U.S.370 (90.5)1.00 Non-U.S.39 (9.5)0.38 ( ) a 0.23 ( ) a Prior Incarceration No65 (15.9)1.00 Yes344 (84.1)0.12 ( ) a 0.06 ( ) a Known TB Contact b No358 (87.5)1.00 Yes51 (12.5)0.83 ( )0.63 ( ) Lived in Shelter c No326 (79.7)1.00 Yes83 (20.3)1.94 ( )2.38 ( ) Intravenous Drug Use No356 (87.0)1.00 Yes53 (13.0)1.08 ( )0.90 ( ) Demographics and Multivariate Logistic Regression for Concordance between TST and QFT-G Assay a p < 0.05 b Known history of contact with a tuberculosis case. c History of living in nursing homes, homeless shelters, drug rehabilitation centers, or “bunk houses”.)