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. 2017 Oct 11;17:674. doi: 10.1186/s12879-017-2798-6

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© The Author(s). 2017

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Fig. 1 — Confirming and excluding power of a positive and negative Xpert test, in smear negative PLHIV with presumptive TB. TB: tuberculosis; Xpert: Xpert MTB/RIF; LR: Likelihood ratio; Pos: positive; Neg: negative; CP: confirming power; EP: excluding power. For a given 61% sensitivity and 99% specificity of Xpert MTB/RIF to detect tuberculosis in smear-negative HIV infected patients with presumptive TB [3], the pre-test probability (prevalence) was 17%, the confirming power of a Xpert result showing “TB detected” was 61 (very strong confirming power), and the excluding power of a Xpert result showing “TB not detected” was 3 (weak excluding power) [13]