Higher Positivity Rate with Fourth-Generation QuantiFERON-TB Gold Plus Assay in Low-Risk U.S. Health Care Workers

Comparison of QuantiFERON-TB Gold In-Tube and QuantiFERON-TB Gold-Plus in the Diagnosis of Mycobacterium tuberculosis Infections in Immunocompromised Patients: a Real-World Study

QuantiFERON-TB Gold Plus (QFT-Plus) is an emerging QuantiFERON test after QuantiFERON-TB Gold In-Tube (QFT-GIT) for tuberculosis infection detection; it is an IFN-γ release assay. We compared QFTPlus, which has an additional TB antigen 2 (TB2) tube to induce cell-mediated (CD8⁺ T cell) immune responses, with QFT-GIT. We conducted this study to assess the agreement of the QFT-GIT and QFT-Plus assays in immunocompromised patients in a clinical setting. A total of 278 immunocompromised patients and 175 immunocompetent patients from different departments were continuously enrolled from August 2020 to March 2021, and each patient underwent both tests. Correlations between QFT-GIT and QFT-Plus assays showed good agreement (κ value = 0.859). Patients receiving long-term immunosuppressant therapy had the lowest concordance between QFT-GIT and QFT-Plus assays; 9 out of 11 positive latent tuberculosis infection (LTBI) cases were diagnosed by the QFT-Plus assay, implying that QFT-Plus may detect more LTBI than QFT-GIT does in these patients. Indeterminate results were associated with lower lymphocyte, CD4⁺ T cell, and CD8⁺ T cell absolute counts, and with lower CD4/CD8 ratios. In conclusion, we found that the QFT-GIT and QFT-Plus assays had high agreement not only in immunocompetent patients but also in immunocompromised patients. QFT-Plus may detect more LTBI than QFT-GIT in patients receiving long-term immunosuppressant therapy. Thresholds were established for lymphocyte absolute counts of >1.15 × 10⁹ cells, and for CD4⁺ T cell absolute counts of >467.7 × 10⁶ to 478.5 × 10⁶ cells, which may lessen the incidence of indeterminate results.

IMPORTANCE This study evaluated the performance of QFT-GIT and QFT-Plus in the diagnosis of M. tuberculosis infection in immunocompromised patients and found that QFT-Plus may detect more LTBI than QFT-GIT does in patients receiving long-term immunosuppressant therapy. We believe that our study makes a significant contribution to the literature because it highlights the different diagnostic accuracies of QFT-GIT and QFT-Plus in different subpopulations of immunocompromised and immunocompetent patients. Selecting a test with better performance, particularly in patients with a high risk of developing active TB, may assist the health sector in better managing TB. Furthermore, we believe that this study will be of significance to the diagnosis of LTBI.

The Impact of Borderline Quantiferon-TB Gold Plus Results for Latent Tuberculosis Screening under Routine Conditions in a Low-Endemicity Setting

Quantiferon-TB Gold Plus (QFT-Plus) is an interferon gamma release assay used to diagnose latent tuberculosis (LTB). A borderline range (0.20 to 0.99 IU/ml) around the cutoff (0.35 IU/ml) has been suggested for the earlier QFT version. Our aims were to evaluate the borderline range for QFT-Plus and the contribution of the new TB2 antigen tube. QFT-Plus results were collected from clinical laboratories in Sweden and linked to incident active TB within 3 to 24 months using the national TB registry. Among QFT-Plus results from 58,539 patients, 83% were negative (<0.20 IU/ml), 2.4% were borderline negative (0.20 to 0.34 IU/ml), 3.4% were borderline positive (0.35 to 0.99 IU/ml), 9.6% were positive (≥1.0 IU/ml), and 1.6% were indeterminate. Follow-up tests after initial borderline results were negative (<0.20 IU/ml) in 38.3%, without any cases of incident active TB within 2 years. Applying the 0.35-IU/ml cutoff, 1.5% of TB1 and TB2 results were discrepant, of which 52% were within the borderline range. A TB2 result of ≥0.35 IU/ml with a TB1 result of <0.20 IU/ml was found in 0.4% (231/58,539) of all included baseline QFT-Plus test results, including 1.8% (1/55) of incident TB cases. A borderline range for QFT-Plus is clinically useful as more than one-third of those with borderline results are convincingly negative upon retesting, without developing incident active TB. The TB2 tube contribution to LTB diagnosis appears limited.

Latent tuberculosis infection among health-care workers using Quantiferon-TB Gold-Plus in a country with a low burden for tuberculosis: prevalence and risk factors

BACKGROUND

Health-care workers (HCW) are susceptible to latent tuberculosis infection (LTBI). The prevalence of LTBI in HCW in Saudi Arabia has not been reported using the fourth-generation interferon gamma release assay QuantiFERON-TB Gold Plus (QFT-Plus).

OBJECTIVE

Determine the prevalence of LTBI in a large heterogeneous HCW population and assess risk factors for LTBI.

DESIGN

Cross-sectional and case-control study.

SETTING

Tertiary academic hospital, Riyadh, Saudi Arabia.

PATIENTS AND METHODS

Medical records of HCWs who had QFT-Plus performed between January to December 2018 were reviewed and included in the cross-sectional study. In a subset analysis, randomly selected positive QFT-Plus cases were compared with controls selected from the same areas of work. Univariate and binary logistic regression analyses were performed to assess the significance of other factors to QFT-PLus positivity.

MAIN OUTCOME MEASURES

Prevalence of LTBI in HCWs and potential risk factors for LTBI.

SAMPLE SIZE

3024 HCWs in the cross-sectional analysis; 294 cases and 294 controls in the case-control analysis.

RESULTS

Twenty-four percent (n=733) of the HCWs had a positive QFT-Plus. The median (interquartile range) age was 34.0 (31.0-37.1) years, 71% were female, and only 24.8% were of Saudi nationals. Nursing represented 57.7% of HCWs, and 24.7% were working in a non-clinical area. Only 20.3% worked in TB-related departments. A higher risk of LTBI was present in HCWs who were older than 50 years (OR=1.95), from either Philippines (OR=4.7) or the Indian subcontinent (OR=4.1), working as a nurse (OR=2.7), allied health profession (OR=2.1), radiology technician (OR=3.1), or in the emergency room (OR=2.4) or intensive care unit (OR=2.1). In the binary logistic regression, independent predictors for positive QFT-Plus were age group older than 50 years (aOR=2.96), known TB exposure (aOR=1.97), and not receiving BCG at birth (aOR=3.08).

LIMITATION

Single-center, retrospective, possible recall bias for BCG vaccination.

CONCLUSION

The high prevalence of LTBI among HCW emphasizes the need to continue pre-employment screening, especially for employed personnel from high endemic areas, with targeted annual screening for the same group and other identified high-risk groups. These findings can aid in the development of national screening guidelines for LTBI in HCW.

CONFLICT OF INTEREST

None.

Diagnostic Tests for Latent Tuberculosis Infection

Diagnosing latent tuberculosis (TB) infection (LTBI) is important globally for TB prevention. LTBI diagnosis requires a positive test for infection and negative evaluation for active disease. Current tests measure an immunologic response and include the tuberculin skin test (TST) and interferon-gamma release assays (IGRAs), T-SPOT.TB and QuantiFERON. The IGRAs are preferred in bacille Calmette-Guérin-vaccinated populations. The TST is still used when cost or logistical advantages over the IGRAs exist. Both TST and IGRAs have low positive predictive values. Tests that differentiate the TB spectrum and better predict future TB risk are needed.

Comparing QuantiFERON-TB Gold Plus with Other Tests To Diagnose Mycobacterium tuberculosis Infection

The fourth-generation QuantiFERON test for tuberculosis infection, QuantiFERON-TB Gold Plus (QFT-Plus) has replaced the earlier version, QuantiFERON-TB Gold In-Tube (QFT-GIT). A clinical need exists for information about agreement between QFT-Plus and other tests. We conducted this study to assess agreement of test results for QFT-Plus with those of QuantiFERON-TB Gold In-Tube (QFT-GIT), T-SPOT.TB (T-SPOT), and the tuberculin skin test (TST). Persons at high risk of latent tuberculosis infection (LTBI) and/or progression to tuberculosis (TB) disease were enrolled at the 10 sites of the Tuberculosis Epidemiologic Studies Consortium from October 2016 through May 2017; each participant received all four tests. Cohen's kappa (κ) and Wilcoxon signed-rank test compared qualitative and quantitative results of QFT-Plus with the other tests. Test results for 506 participants showed 94% agreement between QFT-Plus and QFT-GIT, with 19% positive and 75% negative results. When the tests disagreed, it was most often in the direction of QFT-GIT negative/QFT-Plus positive. QFT-Plus had similar concordance as QFT-GIT with TST (77% and 77%, respectively) and T-SPOT (92% and 91%, respectively). The study showed high agreement between QFT-GIT and QFT-Plus in a direct comparison. Both tests had similar agreement with TST and T-SPOT.

Diagnostic performance in active TB of QFT-Plus assay and co-expression of CD25/CD134 in response to new antigens of Mycobacterium tuberculosis

The new QuantiFERON-TB Gold Plus employs modified peptides optimized to elicit an IFNγ response from CD8⁺ cytotoxic T lymphocytes in addition to CD4⁺ T cells. With a view to improve the difficult identification of TB cases, we assessed the combination of two specific immunological markers comprising IFNγ secretion and T cells co-expression of CD25 and CD134 in response to Mycobacterium tuberculosis-specific antigens. A total of 34 subjects with suspected TB and 10 age-matched HD were prospectively enrolled. Assessing the performance of QFT-Plus in terms of the TB1 and TB2 results, we found that in TB patients, the quantitative IFNγ value in TB2 was similar to that in TB1, and we did not find any differences irrespective of the disease (pulmonary or extra-pulmonary). The flow cytometric CD25/CD134 assay, allowed a more accurate differentiation between M. tuberculosis-infected and uninfected patients, with a better combination of sensitivity and specificity, especially by evaluation of CD4⁺ T-cell subset. All individuals with negative QFT-Plus results displayed a positive CD25/CD134 response. Overall, a positive correlation was found between T cells co-expressing CD25/CD134 and IFNγ levels in response to both QFT-Plus TB antigen tubes, as well as between the QFT-Plus TB1 and TB2 tubes. We demonstrated that both TB1 and TB2 induce a higher expression of CD25⁺CD134⁺ markers on CD4⁺ T cells among infected TB subjects, compared to the lower degree of CD8⁺ T cells, mainly induced to TB2 stimulation. We suggest that a combined use of classic QFT-Plus and specific CD25/CD134 response may be a useful means in the diagnostic workup for active TB.