In patients who are immunocompromised, such as people living with HIV, the new fourth-generation QuantiFERON-TB Gold Plus (QFT-Plus) assay demonstrated similar sensitivity to the third-generation interferon-gamma release assay for the diagnosis of latent tuberculosis (TB), according to study results presented at American Society of Microbiology (ASM) Microbe 2019, held June 20 to 24 in San Francisco, California. In addition, researchers noted that increasing age was strongly correlated with positive results on the assay.

TB is one of the leading causes of death in people with HIV/AIDS, and by adding a second TB antigen tube that can stimulate interferon-gamma release by both CD4+ and CD8+ T cells, the new QFT-Plus offers increased sensitivity and specificity compared with the previous generation assay. Therefore, researchers conducted a prospective study to evaluate the diagnostic performance of the QFT-Plus assay in detecting latent TB in people with HIV compared with the third-generation assay.

The study included 329 adults with HIV. The median CD4 count was 523 cells/μL (interquartile range, 360-699 cells/μL), and 80.6% of the cohort had an undetectable viral load (<20 copies/mL). The prevalence of latent TB infection determined using the third-generation assay and QFT-plus was 7.3%, (95% CI, 4.7%-10.7%). An indeterminate response occurred in 3 cases (0.9%; 95% CI, 0.1%-2.6%). Discordant results occurred in 1.5% of both third-generation assay negative/QFT-Plus-positive cases and third-generation assay positive/QFT-Plus negative cases. The researchers noted that discordant results were not linked to CD4 counts. However, age was a significant risk for positive QFT-Plus results. In patients between age 50 and 59 years, the adjusted odds ratio for positive QFT-Plus was 3.13 (P =.003), and in those aged >60 years, it was 8.57 (P <.001).

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Lee S-J, Lin H-H, Wu K-S, et al. Comparison of two generations of interferon-gamma release assays for diagnosis of latent tuberculosis infection in people living with HIV. Presented at: ASM Microbe 2019; June 20-24, 2019; San Francisco, California. Rapid Fire Session S244.