Evaluation of Xpert MTB/RIF assay performance in diagnosing extrapulmonary tuberculosis among adults in a tertiary care centre in India

To the Editor: According to the World Health Organization Global Tuberculosis Report from 2013, there were 8.6 million incident tuberculosis (TB) cases globally and India alone contributed 26% to this global scenario [1]. Of the five countries with the largest number of TB incident cases in 2012, India tops the list [1]. Epidemiological data suggest that extrapulmonary TB (EPTB) constitutes about 15–20% of all TB cases, but among HIV-TB co-infection it accounts for 50% of the cases [2]. Out of 1 183 373 new TB cases notified globally, 234 029 (20%) were reported to be cases of EPTB [1]. Difficulty in sampling from the extrapulmonary sites and the paucibacillary nature of the specimens make EPTB a diagnostic challenge. Dependency on smear microscopy in these samples may lead to higher false negative rates due to the low sensitivity of this technique. Mycobacterium tuberculosis (MTB) culture is quite a protracted technique, requiring well-trained laboratory personnel, and delay in diagnosis can cause more harm as the treatment is often started empirically. Rapid nucleic acid amplification tests are emerging extensively to provide better yield for rapid diagnosis of TB. The Xpert MTB/RIF (Cepheid, Sunnyvale, CA, USA) is an automated, hemi-nested real-time PCR for detecting MTB complex and rifampin (RIF) resistance, which was initially evaluated for pulmonary specimens in large studies [3–5]. The present communication reports the performance of Xpert MTB/RIF in EPTB samples, with a large sample size from a single centre in a country with a high TB burden. All EPTB samples from indoor as well as outdoor facilities of the All India Institute of Medical Sciences (AIIMS) hospital, New Delhi, India, were received in the Tuberculosis Laboratory (accredited Intermediate Reference Laboratory …