578. The Sum and the Whole of Whole Blood Interferon-gamma Release Assays (IGRAs): Understanding Patient Factors that Influence Quantitative IGRA values in Contact Investigations
Session: Poster Abstract Session: Mycobacterial Diagnostics
Friday, October 21, 2011
Room: Poster Hall B1

In 2010, the Centers for Disease Control proposed reporting quantitative interferon gamma release assay (IFN-g) values to permit a more refined assessment of the results, though it remains unclear which patient factors influence this response.


We reviewed data from the San Francisco Department of Public Health on contacts of cases with culture-confirmed tuberculosis (TB) who were evaluated using QuantiFERON-TB Gold In-Tube (QFT-GIT; Cellestis, Carnegie, Australia) between February 1, 2008 and June 30, 2010.  We excluded contacts who had invalid test results, were found to have active TB, were immunosuppressed, or were under 5 years-old.


Eight hundred ninety-nine contacts of 145 cases met eligibility criteria.  Thirteen percent of contacts had a positive QFT-GIT result (>0.35IU/ml). The median time from exposure to analyzed test result was 12.4 weeks (interquartile range (IQR), 10-16.4 weeks). Median quantitative IFN-g results differed according to case exposure time (0 (IQR 0-0.05), 0.01 (IQR 0-0.09), and 0.04 (IQR 0-0.3) for <100 hours, 100-1000 hours, and >1000 hours, respectively (p<0.05)). In multivariate analysis, age (change in log(IFN-g) per 10 years age, 0.23 (95% CI 0.13-0.32), p<.001), female sex (-0.4 (95% CI -0.75 to -0.05), p=.02), and recent immigration (0.66 (95% CI 0.01-1.32), p=.05) were associated with quantitative IFN-g values.  Race of the contact and mycobacterial burden of the case (as defined by smear-grade or cavitating disease on chest xray) were not associated with quantitative IFN-g values.


Common demographic variables may influence quantitative IFN-g response as measured by QFT-GIT. Cumulative exposure, as represented by recent immigration, may be a more influential predictor of quantitative IFN-g response than recent acute exposure.

Subject Category: D. Diagnostic microbiology

Tara Vijayan, MD1, John Metcalfe, MD, MPH2, Jennifer Grinsdale, MPH3, Christine Ho, MD3, L. Masae Kawamura, MD3, Philip Hopewell, MD2 and Payam Nahid, MD, MPH2, (1)Division of Infectious Diseases, University of California-San Francisco, San Francisco, CA, (2)Pulmonary and Critical Care Medicine, University of California-San Francisco, San Francisco, CA, (3)San Francisco Department of Public Health, San Francisco, CA


T. Vijayan, None

J. Metcalfe, None

J. Grinsdale, None

C. Ho, None

L. M. Kawamura, None

P. Hopewell, None

P. Nahid, 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.