Use of interferon-gamma release assays to calculate the annual risk of tuberculosis infection.

The objective was to assess the annual risk of tuberculosis infection by means of tuberculin skin testing (TST) in children, evaluating whether QuantiFERON-TB Gold In-Tube (QFN-G-IT) could improve the accuracy. On the basis of the positive TST results, the global annual incidence was estimated at 0.78%, with an increase in the prevalence from 0.64% to 1.68% in 2 years. However, QFN-G-IT was only positive in 6 of the 25 children with positive TST. The confirmation of the positive TST results by QFN-G-IT provided more accurate annual incidence estimation.

Dried plasma spots in the diagnosis of tuberculosis: IP-10 release assay on filter paper.

Interferon (IFN)-γ release assays (IGRAs) are probably the most accurate tests for the detection of latent Mycobacterium tuberculosis infection, but IGRAs are labour intensive and the transport of samples over longer distances is difficult. IFN-γ-induced protein (IP)-10 is expressed at 100-fold higher levels than IFN-γ, and IP-10 release assays have comparable performance to IGRAs. The aim of this study was to explore the diagnostic potential of a novel IP-10 release assay based on dried plasma spots (DPS). The presence of IP-10 and IFN-γ was determined in plasma and in DPS by ELISA. Diagnostic algorithms for plasma and DPS tests for IP-10 were developed on a training cohort comprising 60 tuberculosis (TB) patients and 59 healthy controls. Diagnostic accuracy was assessed in a validation cohort comprising 78 TB patients and 98 healthy controls. Plasma was measured in Spain and DPS samples were sent to Denmark using the conventional postal service for analysis. IP-10 was readily detectable in both plasma and DPS, and correlation was excellent (r(2) = 0.95). QuantiFERON-TB Gold In-Tube (QFT-TB) and IP-10 in DPS and plasma rendered comparable sensitivity (78%, 82% and 84%, respectively), specificity (100%, 97% and 97%, respectively) and indeterminate rates (p>0.55). The DPS-based IP-10 test has comparable diagnostic accuracy to the QFT-TB and samples can be sent via conventional mail over long distances for analysis without affecting the results.