Chest
Volume 133, Issue 4, April 2008, Pages 869-874
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Original Research
Mycobacterial Disease
Use of an Interferon-γ Release Assay To Diagnose Latent Tuberculosis Infection in Foreign-Born Patients

https://doi.org/10.1378/chest.07-1815Get rights and content

Background

The tuberculin skin test (TST) has a low specificity in the setting of bacille Calmette-Guérin (BCG) vaccination. Interferon-γ release assays (IGRAs) appear to be more specific but have not been validated in this population under routine clinical conditions. We sought to validate the routine clinical use of the T-SPOT.TB test (Oxford Immunotec; Oxford, UK), an IGRA, in a predominantly foreign-born population with a high rate of BCG vaccination.

Methods

We compared the TST and the T-SPOT.TB test in 96 subjects at a New York City Department of Health tuberculosis clinic. We aimed to determine which test better predicted being a close contact of a case of active tuberculosis, a surrogate for latent tuberculosis infection.

Results

A positive T-SPOT.TB test result was strongly associated with being a close contact of a case of active tuberculosis after adjustment for potential confounders (adjusted odds ratio, 2.9; 95% confidence interval, 1.1 to 7.3; p = 0.03). A positive TST result was associated with being a contact only in subjects without BCG vaccination (p = 0.02). The T-SPOT.TB test was more specific for being a close contact than the TST (p < 0.001). Specificity in BCG-vaccinated subjects was 3% for the TST compared with 70% for the T-SPOT.TB test (p < 0.001).

Conclusions

The T-SPOT.TB test is superior in routine clinical use to the TST for identifying high-risk individuals among foreign-born populations with high rates of BCG vaccination.

Section snippets

Study Subjects

This study was approved by the institutional review boards of the New York City Department of Health and Mental Hygiene (DOHMH) and the Columbia University Medical Center. All subjects provided written, informed consent. We enrolled 123 subjects from a New York City DOHMH tuberculosis clinic from September 8, 2005, through February 21, 2007. Those enrolled included contacts of cases of active tuberculosis (“contacts”) and subjects who were not contacts of patients with active tuberculosis

Excluded Subjects

We enrolled 123 subjects, of whom 27 were excluded. Four subjects never returned to have their TST results read. Three subjects were identified after enrollment who had positive TST results > 6 months prior, and a repeat TST was not done as per protocol. Two subjects were determined to be HIV positive. One subject had been previously treated for LTBI but did not recall this information until after enrollment. Disseminated M bovis infection was diagnosed in one patient. Phlebotomy was

Discussion

We have demonstrated that, compared with TST, the T-SPOT.TB test has improved specificity in identifying a group of subjects at high risk for progression to active tuberculosis, namely, close contacts of cases of active tuberculosis. Our study demonstrates the superiority of the T-SPOT.TB test over the TST under routine clinical conditions in a population critical to tuberculosis control: foreign-born persons from high-prevalence countries with high rates of BCG vaccination. These findings

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Equipment for this study was provided by Oxford Immunotec, Ltd, Oxford, UK.

Dr. Brodie is supported in part by a grant from the Stony Wold-Herbert Fund, Inc. Dr. Schluger is supported in part by the National Institutes of Health/National Heart, Lung, and Blood Institute (K24 HL004074). Dr. Lederer is supported in part by grant RR024157 from the National Institutes of Health.

The authors have no financial or other potential conflicts of interests to disclose.

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