• Pediatr. Infect. Dis. J. · May 2010

    Comparative Study

    Commercial interferon gamma release assays compared to the tuberculin skin test for diagnosis of latent Mycobacterium tuberculosis infection in childhood contacts in the Gambia.

    • Adetifa Ifedayo M O IM Bacterial Diseases Program, Medical Research Council (UK) Laboratories, Fajara, Banjul, The Gambia. iadetifa@mrc.gm, Martin O C Ota, David J Jeffries, Abdulrahman Hammond, Moses D Lugos, Simon Donkor, Owiafe Patrick, Richard A Adegbola, and Philip C Hill.
    • Bacterial Diseases Program, Medical Research Council (UK) Laboratories, Fajara, Banjul, The Gambia. iadetifa@mrc.gm
    • Pediatr. Infect. Dis. J. 2010 May 1; 29 (5): 439-43.

    BackgroundWe compared the performance of tuberculin skin test (TST), Quantiferon-TB Gold in-tube (QFT-GIT), and T-SPOT.TB in diagnosing latent tuberculosis (LTBI) among childhood TB contacts in a TB endemic setting with high BCG coverage. We evaluated the performance of interferon gamma release assays (IGRAs) and TST when combined in an algorithm.MethodsChildhood contacts of newly diagnosed TB patients were tested with TST, QFT-GIT, and T-SPOT. The level of exposure in contacts was categorized according to whether they slept in the same room, same house, or a different house as the index case. For the evaluation of combined test performance, prior estimates for prevalence of latent TB were used in Bayesian models that assumed conditional dependence between tests.ResultsA total of 285 children were recruited. Overall, 26.5%, 33.0%, and 33.5% were positive for TST, T-SPOT, or QFT-GIT, respectively. All 3 tests responded to the gradient of sleeping proximity to the index case. Neither TST nor IGRA results were confounded by BCG vaccination. There was moderate agreement (kappa = 0.40-0.68) between all 3 tests. Combination of either IGRA with TST increased sensitivity (by 9.3%-9.6%) especially in contacts in the highest exposure category but was associated with loss of specificity (9.9%-11.3%).ConclusionIGRAs and TST are similar in their diagnostic performance for LTBI. An approximate 10% sensitivity benefit for using the TST and an IGRA in combination is associated with a slightly greater specificity loss. Testing strategies combining an IGRA and TST with an "or" statement may be useful only in situations where there is a high pretest probability of latent infection.

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