Assessment of the QuantiFERON-TB Gold In-Tube test for the detection of <i>Mycobacterium tuberculosis</i> infection in United States Navy recruits

<div><p>Background</p><p>Immunologic tests such as the tuberculin skin test (TST) and QuantiFERON^®-TB Gold In-Tube test (QFT-GIT) are designed to detect M<i>ycobacterium tuberculosis</i> infection, both latent <i>M</i>. <i>tuberculosis</i> infection (LTBI) and infection manifesting as active tuberculosis disease (TB). These tests need high specificity to minimize unnecessary treatment and high sensitivity to allow maximum detection and prevention of TB.</p><p>Methods</p><p>Estimate QFT-GIT specificity, compare QFT-GIT and TST results, and assess factor associations with test discordance among U.S. Navy recruits.</p><p>Results</p><p>Among 792 subjects with completed TST and QFT-GIT, 42(5.3%) had TST indurations ≥10mm, 23(2.9%) had indurations ≥15mm, 14(1.8%) had positive QFT-GIT results, and 5(0.6%) had indeterminate QFT-GITs. Of 787 subjects with completed TST and determinate QFT-GIT, 510(64.8%) were at low-risk for infection, 277(35.2%) were at increased risk, and none had TB. Among 510 subjects at low-risk (presumed not infected), estimated TST specificity using a 15mm cutoff, 99.0% (95%CI: 98.2–99.9%), and QFT-GIT specificity, 98.8% (95%CI: 97.9–99.8%), were not significantly different (p>0.99). Most discordance was among recruits at increased risk of infection, and most was TST-positive but QFT-GIT-negative discordance. Of 18 recruits with TST ≥15mm but QFT-GIT negative discordance, 14(78%) were at increased risk. TB prevalence in country of birth was the strongest predictor of positive TST results, positive QFT-GIT results, and TST-positive but QFT-GIT-negative discordance. Reactivity to <i>M</i>. <i>avium</i> purified protein derivative (PPD) was associated with positive TST results and with TST-positive but QFT-GIT-negative discordance using a 10 mm cutoff, but not using a 15 mm cutoff or with QFT-GIT results.</p><p>Conclusions</p><p><i>M</i>. <i>tuberculosis</i> infection prevalence was low, with the vast majority of infection occurring in recruits with recognizable risks. QFT-GIT and TST specificities were high and not significantly different. Negative QFT-GIT results among subjects with TST induration ≥15 mm who were born in countries with high TB prevalence, raise concerns.</p></div

Associations between selected subject characteristics and tuberculin skin test or QuantiFERON^®-TB Gold In-Tube test results.

<p>Associations between selected subject characteristics and tuberculin skin test or QuantiFERON^®-TB Gold In-Tube test results.</p

Test agreement.

<p>Test agreement.</p

Results for various cohort subsets.

<p>Results for various cohort subsets.</p

Outcomes of the QuantiFERON^®-TB Gold In-Tube test versus the tuberculin skin test among 856 U.S. Navy recruits who had blood collected and skin test placed.

<p>Outcomes of the QuantiFERON^®-TB Gold In-Tube test versus the tuberculin skin test among 856 U.S. Navy recruits who had blood collected and skin test placed.</p

Diagram of study participants and testing.

<p>QFT = QuantiFERON^®-TB test; QFT-G = QuantiFERON^®-TB Gold test; QFT-GIT = QuantiFERON^®-TB Gold In-Tube test; TST = tuberculin skin test.</p

Comparisons of IFN-γ responses to different antigens measured by commercial ELISA among patients with culture-confirmed tuberculosis.

<p>Median IFN-γ responses (from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026545#pone-0026545-t002" target="_blank">Table 2</a>) to early secreted antigenic target-6 (ESAT-6), culture filtrate protein 10 (CFP-10), TB7.7, and combinations of these antigens for patients with culture-confirmed tuberculosis (patients) are listed with p values in parenthesis calculated by Mann-Whitney U Rank Sum test. Significant differences (<i>p</i><0.05) are indicated in <b>bold type</b>.</p

Cytokine concentrations and responses measured with an in-house MMIA.

<p>Median background cytokine concentrations (Nil, pg/mL) and cytokine responses (pg/mL) to phytohemagglutinin (Mitogen Response), early secreted antigenic target-6 (ESAT-6 Response), culture filtrate protein 10 (CFP-10 Response), TB7.7 (TB7.7 Response), and combinations of these <i>M. tuberculosis</i> (<i>Mtb</i>) antigens (ESAT-6+CFP-10 Response and ESAT-6+CFP-10+TB7.7 Response) are listed with ranges in parentheses. Cytokine concentrations were measured with an in-house multiplexed microsphere-based immunoassay (in-house MMIA) for patients with culture-confirmed tuberculosis (patients) and subjects at low-risk of <i>Mtb</i> exposure (controls). For concentrations that were designated “out of range” by Bio-Plex Manager software, low values are reported as 0 and high values are reported as the upper limit of the standard curve multiplied by the dilution factor (25,000 pg/mL). Responses were calculated by subtracting the background cytokine concentration in plasma from blood incubated with saline (Nil) from the cytokine concentration in plasma from blood incubated with mitogen or <i>Mtb</i> antigens. N = 6 for patients and N = 10 for controls unless indicated (*n = 6). <i>P</i> values were calculated by Mann-Whitney U Rank Sum test comparing cytokine concentrations or responses for patients with controls. Significant differences (<i>p</i><0.05) are indicated in <b>bold type</b>.</p

(A–H): Responses of eight cytokines to specific <i>M. tuberculosis</i> antigens.

<p>Cytokine responses to a peptide cocktail representing early secreted antigenic target-6, culture filtrate protein 10, and TB7.7 (ESAT-6+CFP-10+TB7.7) are depicted for the 12 patients with culture-confirmed tuberculosis (patients) and 12 subjects at low risk for <i>Mtb</i> infection (controls) represented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026545#pone-0026545-t009" target="_blank">Table 9</a>. Cytokine concentrations were measured with a custom commercial multiplexed microsphere-based immunoassay (commercial MMIA). Note the split y-axis. The dotted line and value in parentheses represents the mean cytokine response for controls plus three standard deviations, which was used as a cut point to separate positive and negative responses. <b>Panels A through H</b> depict IFN-γ, IL-2, IL-6, IL-8, TNF-α, IP-10, MCP-1, and MIP-1β responses.</p

Cytokine concentrations and responses measured with a microarray.

<p>Median background cytokine concentrations (Nil, pg/mL) and cytokine responses (pg/mL) to phytohemagglutinin (Mitogen Response), early secreted antigenic target-6 (ESAT-6 Response), culture filtrate protein 10 (CFP-10 Response), TB7.7 (TB7.7 Response), and combinations of these <i>M. tuberculosis</i> (<i>Mtb</i>) antigens (ESAT-6+CFP-10 Response and ESAT-6+CFP-10+TB7.7 Response) are listed with ranges in parentheses. Cytokine concentrations were measured by a commercial quantitative immuno-microaray (microarray) for patients with culture-confirmed tuberculosis (patients) and subjects at low risk for <i>Mtb</i> exposure (controls). Responses were calculated by subtracting the background cytokine concentration in plasma from blood incubated with saline (Nil) from the cytokine concentration in plasma from blood incubated with mitogen or <i>Mtb</i> antigens. Cytokine responses for some patients and controls were not determined due to poor performance of the respective standard curves. N = 5 or 6 for patients subjects and N = 6 or 7 for controls unless indicated (*n = 4, **n = 5). <i>P</i> values were calculated by Mann-Whitney U Rank Sum test comparing cytokine concentrations or responses for patients with controls. Significant differences (<i>p</i><0.05) are indicated in <b>bold type</b>.</p