Interferon-gamma release assay for detection of latent tuberculosis infection in casual and close contacts of tuberculosis cases.

The tuberculin skin test (TST) has many limitations for the diagnosis of latent tuberculosis (TB infection. The aim of this study in Egypt was to estimate the usefulness of an interferon-gamma release assay (IFN-gamma) assay for the detection of latent TB infection in contacts of active TB cases. A total of 116 participants were enrolled and divided into 3 groups: community controls, casual (laboratory and clinic) contacts and close (household) contacts. Subjects diagnosed with latent TB infection by TST were 11.5% of controls, 71.1% of casual contacts and 29.6% of close contacts. Subjects diagnosed as latent TB infection by IFN-gamma assay (QuantiFERON-TB Gold In-Tube) were 5.9% of controls, 31.0% of casual contacts and 33.3% of close contacts. The overall agreement between TST and IFN-gamma was 66.7% (kappa = 0.28). The IFN-gamma method could be more helpful than TST for detection of latent TB infection in contacts.