Background and objective
Until recently, the only tool for detection of latent tuberculosis infection (LTI) was the tuberculin skin test (PPD). QuantiFERON?-TB Gold In-Tube (QF), as well as other Mycobacterium tuberculosis-specific interferon-¦Ã release assays (IGRAs), appears to be an alternative or adjunct to the PPD. The goal of the study was to compare QF with PPD to evaluate de accuracy of QF for routinely identifying LTI in contact investigations.
Patients and method
We performed a descriptive and prospective study with contacts of culture-confirmed tuberculosis source cases in Bizkaia and Araba from May 2007 through February 2008 who underwent QF and PPD. Concordance between both tests was analyzed using the kappa statistic (¦Ê).
Results
376 contacts were found: 8 were high-risk children (age < 15), 30 low-medium risk children, 46 high-risk adults (age > 14) and 270 low-medium risk adults. PPD was positive in 160 subjects (42.5 % ) at PPD ?5 mm, 141 (37.5 % ) at PPD ?10 mm and 95 (25.3 % ) at PPD ?15 mm. In QF analysis 94 subjects were positive, 279 negative and 3 indeterminate. Overall agreement between QF and PPD was good at PPD ?10 mm (¦Ê = 0.53; p < 0.0001) but agreement was poor when the index case had positive baciloscopy at PPD ?5 mm (¦Ê = 0.28; p < 0.001) and high-risk contacts at PPD ?15 mm (¦Ê = 0.048; p = 0.36).
Conclusions
IGRAs are an accurate indicator of LTI, providing a more specific way of diagnostic and reducing the number of subjects to be treated. QF appears to be a valuable public health tool with potential advantages over the PPD and improving resources.
