Discordance between the QuantiFERON Gold In-Tube and QuantiFERON Gold Plus assays associated with country of birth TB incidence.

BACKGROUND: The new QuantiFERON Gold Plus (QFT+) assay is used for diagnosing tuberculosis (TB) infection and has 2 phlebotomy methods: direct (QFT + D) and single tube transfer (QFT + T). Little data is available on how the TB incidence in the country of birth (COB) of healthcare workers (HCWs) can impact the assay results. METHODS: QuantiFERON Gold In-Tube (QFT-G), QFT + D and QFT + T assays were obtained from a single blood draw and compared for HCWs annually tested for TB infection. HCWs COB was ranked as: high (≥150 per 100,000), medium (20-149), and low TB incidence (<20 TB cases). RESULTS: In 265 HCWs, QFT-G/+D/+T results from medium TB incidence COB (15.6%, 16.9% and 22.1%) were more likely to be positive than high (9.7%, 11.8% and 16.1%) or low incidence COB (6.3%, 8.4% and 10.5%). Agreement between assay results for high, medium and low TB incidence COB were: 95.7%, 83.1%, and 95.8% between QFT-G/QFT + D (p = 0.003), 91.4%, 88.3% and 95.8% between QFT-G/QFT + T (p = 0.187), and 91.4%, 76.6%, and 91.6% between QFT + D/QFT + T (p = 0.005). CONCLUSION: Lower agreement and a higher proportion of positivity were found in QFT-G/+D/+T results in individuals from medium TB incidence COB. QFT + may be more sensitive than QFT-G in HCWs from medium TB incidence COB.

Evaluating an Education Program to Reduce Indeterminate QuantiFERON Gold In-Tube Results.

BACKGROUND: The QuantiFERON Gold In-Tube (QFT-G) assay is used to identify individuals with tuberculosis infection and gives quantitative and qualitative results including positive, negative, or indeterminate results (that cannot be interpreted clinically). Several factors, including immunosuppression and preanalytical factors, have been suggested to be significantly associated with indeterminate QFT-G results. An online education program was designed and implemented to reduce the rate of indeterminate QFT-G test results at Houston Methodist Hospital (HMH). METHODS: Data from patients' electronic medical records having indeterminate QFT-G results between 01/2015 and 05/2016 at HMH in Houston, TX, were administratively extracted for (1) medical unit where QFT-G phlebotomy was performed, (2) demographics, and (3) ICD-9/10 diagnosis codes. Unit nurses identified with high proportions of indeterminate QFT-G results were emailed a link to an online pretest educational program with a QFT-G blood collection and handling presentation, and a posttest assessment. RESULTS: Of the 332 nurses emailed, 94 (28.4%) voluntarily completed both tests within the 6-month time allotted. The nurses that completed the education program had a significantly higher posteducation test score than on the pretest (70.2% versus 55.3%, p<0.001, effect size=0.82). Improved posttest score was seen in 67.0% of participants. No reduction in the proportion of indeterminate test results was seen overall at HMH in the 6 months after education. CONCLUSIONS: A targeted education program was able to successfully increase nurses' knowledge of blood collection and handling procedures for the QFT-G test, but no association was found between the improvement of posttest score and indeterminate QFT-G test results.

Performance and variability of QuantiFERON Gold Plus assay associated with phlebotomy type.

BACKGROUND: QuantiFERON Gold Plus (Plus) assay has two approved methods for blood collection: direct in-tube (Plus direct) or the transfer of blood from a lithium heparin tube (Plus transfer). Currently, there is little data comparing the results of Plus and the QuantiFERON Gold In-Tube (Gold) based on blood collection. METHODS: In 2017, high risk healthcare workers undergoing annual tuberculosis infection screening at Houston Methodist Hospital, a private hospital in the Texas Medical Center (Houston, TX, U.S.A.) were consented and enrolled in a study comparing the Gold-in-tube (Gold), Plus direct in-tube, and Plus transfer assays. Blood was drawn concurrently for all 3 assays. RESULTS: Phlebotomy occurred on 300 consecutive, consented and enrolled participants in the study. The proportion of positive test results for the Gold, Plus direct and Plus transfer assays were 10% (29/300), 12% (35/299) and 17% (51/299), respectively. The agreement in the results of Gold versus Plus direct, Gold versus Plus transfer, and Plus direct versus Plus transfer was 91%, kappa (κ) = 0.56; 91%, κ = 0.59; and 85%, κ = 0.37, respectively. CONCLUSIONS: Among high risk healthcare workers in a low prevalence tuberculosis setting, the Gold Plus assay had a higher proportion of positive results than the Gold in-tube assay. The agreement between the Gold, Plus direct and Plus transfer assays was unexpectedly low for simultaneously obtained samples. Blood transfer using lithium heparin offers individual clinics and public health programs greater ability to customize protocols, but variability of results still exists.

Differential positive TSPOT assay responses to ESAT-6 and CFP-10 in health care workers.

BACKGROUND: The TSPOT.TB (TSPOT) diagnostic test for latent tuberculosis infection is based on a cell-mediated response to the Mycobacteria tuberculosis antigens, ESAT-6 and/or CFP-10, producing an "interferon-gamma footprint". We investigated the within-sample and within-subject variability of positive TSPOT assays due to the individual assay antigens' reactivity. METHODS: Positive TSPOT assay frequencies due to ESAT-6 or CFP-10 among health care workers (HCWs) at 6-month intervals for 18 months were compared. Differences in result interpretation (positive or negative) for ESAT-6 and CFP10 and potential prognostic factors were investigated. RESULTS: There were 576 positive results in 8805 TSPOT assays representing 2418 participants. A significant difference was detected in positive TSPOT results due to a positive response to either ESAT-6, CFP-10 or both antigens at baseline through 12 M (p < 0.001), but not for the 18 M follow-up. Gender, ethnicity, occupation, previous positive tuberculin skin test (TST) and study site were significantly associated with specific antigen positivity. CONCLUSIONS: Among our HCW samples with positive TSPOT assays, CFP-10 induced a larger proportion of positive TSPOT results than ESAT-6. Potential causes for this finding include: BCG vaccinated subpopulations, certain jobs, history of positive TST, U.S. birth, and study site. A high proportion of single-positive specimens may reflect false-positives results.

Comparing TSPOT assay results between an Elispot reader and manual counts.

BACKGROUND: The interferon gamma release assay, TSPOT.TB (TSPOT) can be read by several methodologies, including an Elispot reader or manually by technician. We compared the results from these two counting methods. METHODS: Automated and manual TSPOT results among 2481 United States health care workers were compared. Cohen's kappa coefficient was used to determine the inter-rater agreement. Univariate and multiple logistic regression were used to investigate selected variable contributions. RESULTS: No prognostic factors were associated with agreement of TSPOT results between counting methods. Agreement between TSPOT results were 92.3%, 89.5%, 93.0%, and 93.1% at baseline, and at follow-up at 6, 12, and 18 months, respectively. The inter-rater agreement for all test results was good (kappa = 0.71). There was a significant difference between individual technicians kappa coefficients (p < 0.001), but no significant increase in agreement over time for technicians (p = 0.394). CONCLUSION: Commercial Elispot readers and manual counts have good agreement of TSPOT results in a low TB burden setting. Levels of agreement differed between individual technicians and automated reader from moderate to very good, indicating borderline results may be misinterpreted due to inter-rater variability. With no latent tuberculosis infection (LTBI) gold standard, it cannot be determined if one TSPOT reading method is better than another.

Test variability of the QuantiFERON-TB gold in-tube assay in clinical practice.

RATIONALE: Although IFN-γ release assays (IGRAs) are widely used to screen for Mycobacterium tuberculosis infection in high-income countries, published data on repeatability are limited. OBJECTIVES: To determine IGRA repeatability. METHODS: The study population included consecutive patients referred to The Methodist Hospital (Houston, TX) between August 1, 2010 and July 31, 2011 for latent tuberculosis (TB) infection screening with an IGRA (QuantiFERON-TB Gold In-Tube; Cellestis, Carnegie, Australia). We performed multiple IGRA tests using leftover stimulated plasma according to a prospectively formulated quality control protocol. We analyzed agreement in interpretation of test results classified according to manufacturer-recommended criteria and repeatability of quantitative TB response. MEASUREMENTS AND MAIN RESULTS: During the study period, 1,086 test results were obtained from 543 subjects. Per the manufacturer's cut-point, the result of the second test was discordant from that of the first in 28 (8%) of 366 patients with valid test results, including 13 with an initial negative result and 15 with an initial positive result. Although agreement between repeat test results was high (κ = 0.84; 95% confidence interval, 0.79-0.90), the normal expected range of within-subject variability in TB response on retesting included differences of ± 0.60 IU/ml for all individuals (coefficient of variation, 14%), and ± 0.24 IU/ml (coefficient of variation, 27%) for individuals whose initial TB response was between 0.25 and 0.80 IU/ml. CONCLUSIONS: There is substantial variability in TB response when IGRAs are repeated using the same patient sample. IGRA results should be interpreted cautiously when TB response is near interpretation cut-points.

Incidence of moxifloxacin resistance in clinical Mycobacterium tuberculosis isolates in Houston, Texas.

Comprehensive data on the prevalence of quinolone resistance in Mycobacterium tuberculosis clinical isolates in the United States are scarce. By use of a systematic population-based approach, M. tuberculosis strains from tuberculosis (TB) cases were collected in Harris County, TX, in 2007 to 2008. The susceptibilities of M. tuberculosis isolates to moxifloxacin and ofloxacin were determined by the agar proportion indirect susceptibility method. Spoligotyping and 12-locus mycobacterial interspersed repetitive unit (MIRU12)-based genotyping of M. tuberculosis isolates were performed, and the gyrA, gyrB, Rv2686c, Rv2687c, and Rv2688c genes in quinolone-resistant and year-of-diagnosis-matched M. tuberculosis isolates were sequenced. Susceptibility testing was performed on 557 M. tuberculosis isolates, of which 10 (1.8%) were resistant to moxifloxacin. There was 100% concordance between ofloxacin and moxifloxacin susceptibilities. A quinolone was prescribed to at least 5 (50%) patients in the period preceding TB diagnosis. Multidrug-resistant TB (MDR-TB) was significantly associated with quinolone resistance (P = 0.01). Mutations in the quinolone resistance-determining region of gyrA were found for 50% of the resistant isolates. No other presumptive quinolone resistance-associated mutations were identified. We conclude that the incidence of moxifloxacin-resistant TB is low in Harris County and is associated with MDR-TB. Previous exposure to quinolones is common among patients with moxifloxacin resistance and warrants more careful evaluation.

Polymorphic allele of human IRGM1 is associated with susceptibility to tuberculosis in African Americans.

An ancestral polymorphic allele of the human autophagy-related gene IRGM1 is associated with altered gene expression and a genetic risk for Crohn's Disease (CD). We used the single nucleotide polymorphism rs10065172C/T as a marker of this polymorphic allele and genotyped 370 African American and 177 Caucasian tuberculosis (TB) cases and 180 African American and 110 Caucasian controls. Among African Americans, the TB cases were more likely to carry the CD-related T allele of rs10065172 (odds ratio of 1.54; 95% confidence interval, 1.17-2.02; P<0.01) compared to controls. Our finding suggests that this CD-related IRGM1 polymorphic allele is also associated with human susceptibility to TB disease among African Americans.

Enhancement of human antigen-specific memory T-cell responses by interleukin-7 may improve accuracy in diagnosing tuberculosis.

Children and immunocompromised adults are at an increased risk of tuberculosis (TB), but diagnosis is more challenging. Recently developed gamma interferon (IFN-gamma) release assays provide increased sensitivity and specificity for diagnosis of latent TB, but their use is not FDA approved in immunocompromised or pediatric populations. Both populations have reduced numbers of T cells, which are major producers of IFN-gamma. Interleukin 7 (IL-7), a survival cytokine, stabilizes IFN-gamma message and increases protein production. IL-7 was added to antigen-stimulated lymphocytes to improve IFN-gamma responses as measured by enzyme-linked immunosorbent assay (ELISA) and enzyme-linked immunospot (ELISPOT) assay. Antigens used were tetanus toxoid (n = 10), p24 (from human immunodeficiency virus [HIV], n = 9), and TB peptides (n = 15). Keyhole limpet hemocyanin was used as a negative control, and phytohemagglutinin was the positive control. IL-7 improved antigen-specific responses to all antigens tested including tetanus toxoid, HIV type 1 p24, and TB peptides (ESAT-6 and CFP-10) with up to a 14-fold increase (mean = 3.8), as measured by ELISA. Increased IFN-gamma responses from controls, HIV-positive patients, and TB patients were statistically significant, with P values of <0.05, 0.01, and 0.05, respectively. ELISPOT assay results confirmed ELISA findings (P values of <0.01, 0.02, and 0.03, respectively), with a strong correlation between the two tests (R(2) = 0.82 to 0.99). Based on average background levels, IL-7 increased detection of IFN-gamma by 39% compared to the level with antigen alone. Increased production of IFN-gamma induced by IL-7 improves sensitivity of ELISA and ELISPOT assays for all antigens tested. Further enhancement of IFN-gamma-based assays might improve TB diagnosis in those populations at highest risk for TB.