576. Screening for Latent Tuberculosis (TB) Infection in a Low TB-endemic Population: A Comparison of QuantiFERONŽ-TB Gold In-Tube (QFT) and Tuberculin Skin Testing (TST)
Session: Poster Abstract Session: Mycobacterial Diagnostics
Friday, October 21, 2011
Room: Poster Hall B1
  • Amick IDSA final.pdf (504.4 kB)
  • Background: 

    Screening for latent TB infection in healthcare providers (HCPs) is a requirement for all healthcare institutions.  Both compliance with annual and post-exposure testing and accurate TB screening test results are essential to prevent transmission within the healthcare setting and community and to help determine appropriate therapy.  Northwestern Memorial Hospital (NMH) HCPs have traditionally been a low-TB endemic population, and we first introduced QFT screening for our HCPs in 2009.  We sought to compare performance of QFT and TST among HCPs within our institution. 


    First, a retrospective cohort study was conducted to collect QFT test results at hire and historical TST test results (within 2 months to 2 years of hire) for incoming 2009 housestaff.  Agreement between TST and QFT was quantified using positive and negative proportion agreement and the kappa statistic.  Second, QFT use was expanded to all NMH staff in January 2010.  Following this, a time-series analysis was conducted to evaluate the performance of these two tests in all HCPs in 2009 compared with 2010.  Conversion rates and compliance with testing were evaluated in both time periods.


    For housestaff, 181 individuals had both historical TST and new hire QFT test results available.  Of these, 19 (10%) had discordant results: 11 TST positive/QFT negative and 8 TST negative/QFT positive.  Overall agreement between test results was 90%. Negative agreement was 0.94; whereas, positive agreement was 0.24, giving an overall kappa statistic of 0.1845.  For all NMH HCPs, the conversion rate was 0.14% in 2009 (3 of 2100) compared with 1.5% (112 of 7472) in 2010.  Testing compliance was less than 30% in 2009 and increased to 95% in 2010 with the implementation of QFT.


    Use of QFT in our workforce led to an unexpected ten-fold rise in our conversion rate despite our low-TB endemic population.  Although overall test agreement was poor, negative test results were much more likely to agree than positive results. The introduction of QFT significantly improved our compliance. This study suggests that, in a low-TB endemic population when compliance with screening is required, use of QFT is an acceptable alternative to TST, but that positive results may require further investigation.

    Subject Category: N. Hospital-acquired and surgical infections, infection control, and health outcomes including general public health and health services research

    Alexandra Amick, BSc, MPH, Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL, Cara Coomer, BSN, RN, CIC, Infection Control and Prevention, Northwestern Memorial Hospital, Chicago, IL, Susheel Reddy, MPH, Division of Infectious Disease, Northwestern University Feinberg School of Medicine, Chicago, IL, Rebecca Wurtz, MD, MPH, Department of Preventive Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL, Daniel Samo, MD, Northwestern Memorial Physicians Group, Chicago, IL and Teresa Zembower, MD, MPH, Department of Infectious Diseases, Northwestern University Feinberg School of Medicine, Chicago, IL


    A. Amick, None

    C. Coomer, None

    S. Reddy, None

    R. Wurtz, None

    D. Samo, None

    T. Zembower, None

    Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.