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JAMA. 2005 Jun 8;293(22):2746-55.

Mycobacterium tuberculosis infection in health care workers in rural India: comparison of a whole-blood interferon gamma assay with tuberculin skin testing.

Author information

1
Department of Medicine, Mahatma Gandhi Institute of Medical Sciences, Sevagram, India. madhupai@berkeley.edu

Abstract

CONTEXT:

Mycobacterium tuberculosis infection in health care workers has not been adequately studied in developing countries using newer diagnostic tests.

OBJECTIVES:

To estimate latent tuberculosis infection prevalence in health care workers using the tuberculin skin test (TST) and a whole-blood interferon gamma (IFN-gamma) assay; to determine agreement between the tests; and to compare their correlation with risk factors.

DESIGN, SETTING, AND PARTICIPANTS:

A cross-sectional comparison study of 726 health care workers aged 18 to 61 years (median age, 22 years) with no history of active tuberculosis conducted from January to May 2004, at a rural medical school in India. A total of 493 (68%) of the health care workers had direct contact with patients with tuberculosis and 514 (71%) had BCG vaccine scars.

INTERVENTIONS:

Tuberculin skin testing was performed using 1-TU dose of purified protein derivative RT23, and the IFN-gamma assay was performed by measuring IFN-gamma response to early secreted antigenic target 6, culture filtrate protein 10, and a portion of tuberculosis antigen TB7.7.

MAIN OUTCOME MEASURES:

Agreement between TST and the IFN-gamma assay, and comparison of the tests with respect to their association with risk factors.

RESULTS:

A large proportion of the health care workers were latently infected; 360 (50%) were positive by either TST or IFN-gamma assay, and 226 (31%) were positive by both tests. The prevalence estimates of TST and IFN-gamma assay positivity were comparable (41%; 95% confidence interval [CI], 38%-45% and 40%; 95% CI, 37%-43%, respectively). Agreement between the tests was high (81.4%; kappa = 0.61; 95% CI, 0.56-0.67). Increasing age and years in the health profession were significant risk factors for both IFN-gamma assay and TST positivity. BCG vaccination had little impact on TST and IFN-gamma assay results.

CONCLUSIONS:

Our study showed high latent tuberculosis infection prevalence in Indian health care workers, high agreement between TST and IFN-gamma assay, and similar association between positive test results and risk factors. Although TST and IFN-gamma assay appear comparable in this population, they have different performance and operational characteristics; therefore, the decision to select one test over the other will depend on the population, purpose of testing, and resource availability.

PMID:
15941804
DOI:
10.1001/jama.293.22.2746
[Indexed for MEDLINE]
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