Xpert MTB/RIF, a new pillar in the diagnosis of extrapulmonary tuberculosis?
10-15% of tuberculosis (TB) cases in India are estimated to have extrapulmonary disease and due to lack of diagnostic means, often remain untreated. Early detection of Mycobacterium tuberculosis (MTB) and multi-drug resistance is a priority in TB diagnosis to improve the successful treatment rate of TB and reduce transmission. Xpert MTB/RIF test (Xpert) - recently endorsed by World Health Organization for the detection of pulmonary TB - was evaluated to test its utility in 546 patients suspected of extrapulmonary tuberculosis. 546 extrapulmonary specimens were split and processed simultaneously for both culture (solid and liquid) and Xpert. For culture, the sensitivity was low - 53% (150/283). Results of Xpert sensitivity and specificity were assessed in comparison to a composite reference standard made up of smear and culture results, clinical, radiological and histological findings. The sensitivity of Xpert was 81% (228/283), (64% [89/138] for smear negative cases and 96% [139/145] for smear positive cases), with a specificity of 99.6%. The sensitivity was found to be high for the majority of specimen types (63-100%) except for cerebrospinal fluid, which was 29% (2/7). Xpert correctly identified 98% of phenotypic Rifampin (RIF) resistant cases and 94% of phenotypic RIF susceptible cases. Sequencing of the 6 discrepant samples resolved 3 of them, resulting in an increased specificity of 98%. In conclusion, the results of this study suggest that Xpert also shows good potential in the diagnosis of extrapulmonary TB and that its ease of use makes it applicable for TB endemic countries.
Anon. Xpert MTB/RIF: a New Pillar in Diagnosis of Extrapulmonary Tuberculosis? Journal of Clinical Microbiology (2011) 49 (7) 2540-2545. [DOI: 10.1128/JCM.02319-10]