Evaluation of QuantiFERON TB gold plus among TB household contacts in high incidence settings

Accurately identifying and categorizing individuals who are latently infected is critical for developing prevention strategies against tuberculosis (TB) disease. The QuantiFERON-TB Gold Plus (QFT-Plus), a set of two antigen tubes, was used to assess TB household contacts, aiming to induce CD4 + and CD8 + T cell responses.

We examined fifty-six TB household contacts for TB infection using the QFT-Plus and QFT-Gold In-Tube (QFT-GIT) tests. In addition, we evaluated 616 samples from the parent study to determine whether there was any association between the QFT-Plus CD8 + T cell responses and variables that were clinically significant. This was done by analyzing the difference in interferon-gamma (IFNγ) levels between TB2 and TB1 tubes. We utilised a cut-off of 0.6 IU/mL.

To assess agreement between tests, a Cohen's kappa of 0.71 was observed across 56 TB contacts. Eight participants reported discordance: four reported positive QFT-Plus and negative QFT-GIT, and four reported negative QFT-Plus and positive QFT-GIT. The QFT-Plus CD8 + T cell responses did not show any significant correlation with the age, sex, history of BCG vaccination, HIV infection, TB risk score and baseline blood draw among adult TB household contacts.

The QFT-Plus and QFT-GIT tests significantly agree with one another. No clinically significant variable was observed to be associated with CD8 + T cell responses in QFT-Plus.