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TB Notes 3, 2006
Introduction
Highlights from State and Local Programs
  Art Therapy Helps Isolated Patients: Exhibition at Bellevue Hospital Center
  Surgeon General Visits Clinic in Hawaii
DTBE World TB Day Activities
National TB Controllers’ Association Poster Contest
EIS Conference a Success for DTBE
Regional Training and Medical Consultation Centers’ Needs Assessments
Laboratory Update
Communications, Education, and Behavioral Studies Branch Updates
TB Education and Training Network Update
  Member Highlight
  Cultural Competency Subcommittee
TB Epidemiologic Studies Consortium Update
  TBESC Task Order 6 (TO6) Update: Regional Capacity-Building in Low-Incidence Areas
  New TBESC Study to Be Launched: Evaluation of New Interferon-gamma Release Assays in the Diagnosis of Latent TB Infection in Health Care Workers
New CDC Publications
Personnel Notes
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TB Notes Newsletter

No. 3, 2006

TUBERCULOSIS EPIDEMIOLOGIC STUDIES CONSORTIUM

New TBESC Study to Be Launched: Evaluation of New Interferon-gamma Release Assays in the Diagnosis of Latent TB Infection in Health Care Workers

Principal Investigator: Chuck Daley

Co-Principal Investigators: Nick Deluca, Jerry Mazurek, Susan Dorman

The TBESC is planning a new study titled “Evaluation of New Interferon-gamma Release Assays in the Diagnosis of Latent Tuberculosis Infection in Health Care Workers.” The study will evaluate the test characteristics, feasibility, and cost-effectiveness of interferon-gamma release assays (IGRAs) and the tuberculin skin test (TST) when testing for LTBI in health care workers (HCWs) at 4 to 6 TBESC sites.

HCWs make up a critical study population for IGRAs. According to the Labor Department, there are approximately 14 million HCWs in the United States, most of whom undergo serial skin testing. HCWs represent a diverse yet stable and accessible population with a wide range of rates of LTBI and risks of TB exposure. Testing them is costly and time consuming, but detection of new infection is necessary for discovering M. tuberculosis transmission and for preventing occupation-related TB. The consequences of missing TB in a HCW are potentially disastrous (CDC. MMWR 2004: MMWR 2005).

Until recently the only method for detecting infection was the TST, which requires two-step testing for the initial evaluation. The TST has a number of important deficiencies: it lacks sensitivity and specificity, its results are influenced by BCG vaccination, and it requires two health care visits to obtain results. IGRAs have excellent sensitivity and specificity and provide some advantages over the TST. IGRAs require one health care visit, the result can be available within one day, and interpreting the test results is less subjective than for the TST. Many HCWs in the United States were born in countries where the incidence of TB is high and where BCG vaccination is routine. IGRAs using region-of-difference 1 antigens are not influenced by BCG vaccination, which may increase HCW confidence in the result.

IGRAs must be evaluated longitudinally in HCWs to determine the frequency of reversion and conversion, to determine the optimal definition of conversion, and to study the repeatability and reproducibility of these new tests. Because a switch from skin testing to IGRAs will represent a major change in our approach to testing HCWs, it is important to assess the utilization and acceptability of these new tests among patients and providers. Given the large number of HCWs in the United States, it is important to evaluate the cost-effectiveness of the different testing methods in health care settings.

The specific aims of the study are as follows:

  1. To determine and compare the test characteristics (estimated sensitivity and specificity) of two IGRAs (QuantiFERON TB Gold [QFT-G] and T-Spot.TB) compared with each other and to the TST at initial testing.
  2. To determine and compare the repeatability and reproducibility of the results.
  3. To determine and compare the test characteristics of the two IGRAs compared with the TST in detecting the phenomena of “conversion” and “reversion.”
  4. To determine and compare the costs, cost differences, and cost-effectiveness of the three methods.
  5. To determine and compare the feasibility of the three methods for serial testing of HCWs.
  6. To determine and compare the acceptability and usability of the IGRAs compared with the TST among patients and providers.
  7. To determine the extent to which, if any, the TST causes boosting of results from the IGRAs.
  8. To observe how treating LTBI influences test results longitudinally.

After providing written consent, approximately 3000 HCWs from four to six TBESC sites will undergo a standardized interview and will be tested serially with all three tests, except for subjects who have 15 mm or greater of induration; they will be tested with the two IGRAs. Test results will be recorded as currently recommended by manufacturers’ and national guidelines (MMWR, December 2005) and numerical output (i.e., the number of spot-forming cells and amount of interferon gamma produced) from the IGRAs will be recorded in order to determine the optimal definition for conversion. For HCWs who have two-step testing, two IGRAs will be repeated with the TST to observe whether the initial TST influences results from the IGRAs. A sample of HCWs will have each test performed twice at the initial testing in order to assess the repeatability of the assays. HCWs will be retested every 6 months after the initial testing until they have been retested at least three times (a total of four testings). The influence of treating LTBI will be studied by comparing longitudinal test results in HCWs who do and do not receive treatment. Direct and indirect costs will be calculated for each test method for comparing costs for each strategy and determining cost-effectiveness. The acceptability and usability of the IGRAs by providers and the acceptability of the testing procedures by the patients will be assessed using qualitative methodology.

Submitted by Chuck Daley and Rachel Albalak
TBESC

 


Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination - http://www.cdc.gov/tb

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