Abstract

BackgroundThe whole-blood interferon-gamma release assay (IGRA) is recommended in some settings as an alternative to the tuberculin skin test (TST). Outcomes from field implementation of the IGRA for routine tuberculosis (TB) testing have not been reported. We evaluated feasibility, acceptability, and costs after 1.5 years of IGRA use in San Francisco under routine program conditions.MethodsPatients seen at six community clinics serving homeless, immigrant, or injection-drug user (IDU) populations were routinely offered IGRA (Quantiferon-TB). Per guidelines, we excluded patients who were <17 years old, HIV-infected, immunocompromised, or pregnant. We reviewed medical records for IGRA results and completion of medical evaluation for TB, and at two clinics reviewed TB screening logs for instances of IGRA refusal or phlebotomy failure.ResultsBetween November 1, 2003 and February 28, 2005, 4143 persons were evaluated by IGRA. 225(5%) specimens were not tested, and 89 (2%) were IGRA-indeterminate. Positive or negative IGRA results were available for 3829 (92%). Of 819 patients with positive IGRA results, 524 (64%) completed diagnostic evaluation within 30 days of their IGRA test date. Among 503 patients eligible for IGRA testing at two clinics, phlebotomy was refused by 33 (7%) and failed in 40 (8%). Including phlebotomy, laboratory, and personnel costs, IGRA use cost $33.67 per patient tested.ConclusionIGRA implementation in a routine TB control program setting was feasible and acceptable among homeless, IDU, and immigrant patients in San Francisco, with results more frequently available than the historically described performance of TST. Laboratory-based diagnosis and surveillance for M. tuberculosis infection is now possible.

Highlights

  • The whole-blood interferon-gamma release assay (IGRA) is recommended in some settings as an alternative to the tuberculin skin test (TST)

  • BMC Infectious Diseases 2006, 6:47 http://www.biomedcentral.com/1471-2334/6/47 and difficulty in interpreting results in patients previously vaccinated with bacille Calmette Guerin (BCG) or with non-tuberculosis mycobacterial (NTM) infection. [1,2] Patients may find the test inconvenient because they must return in 48–72 hours for result reading and interpretation

  • Laboratory-based testing for M. tuberculosis infection could in theory overcome the technical and operational limitations of the TST, but until recently no such test was commercially available in the United States

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Summary

Introduction

The whole-blood interferon-gamma release assay (IGRA) is recommended in some settings as an alternative to the tuberculin skin test (TST). Providers in the United States and Europe have for many years relied on the tuberculin skin test (TST) to detect infection with Mycobacterium tuberculosis in patients. Laboratory-based testing for M. tuberculosis infection could in theory overcome the technical and operational limitations of the TST, but until recently no such test was commercially available in the United States. Known as the QuantiFERON®-TB test (Cellestis International, Carnegie, Australia), this assay provides information about patients' cell-mediated immune response to M. tuberculosis by measuring interferon-γ produced in whole blood after incubation with purified protein derivative (PPD) from M. tuberculosis [3] Use of this interferon-γ release assay (IGRA) for detection of M. tuberculosis infection has been reported in several research studies and in small hospitalor laboratory-based implementations [4,5,6,7,8]

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