Xpert(®) MTB/RIF for improved case detection of extra-pulmonary TB in a tertiary care setting in urban India

Department of microbiology at a tertiary care hospital, Mumbai, India.

To determine 1) the sensitivity and specificity of the Xpert(®) MTB/RIF assay in comparison with microscopy and culture in extra-pulmonary tuberculosis (EPTB), and 2) the number of additional cases of EPTB and rifampicin (RMP) resistance detected using this assay.

The study was conducted from July 2013 to April 2015. All consecutive patients with clinically suspected EPTB referred for microscopic examination to the Department of Microbiology that were sufficient in specimen volume were included in the study.

Of the 728 specimens included in the study, respectively 5.5%, 23.5% and 20.9% were positive on smear, culture and Xpert. Compared to culture, Xpert had a sensitivity of 84.2% (95%CI 81.4-86.6) and specificity of 98.2% (95%CI 90-104). All specimens with high and medium load on assay were positive on culture; 28 (18.4%) specimens were RMP-resistant and 124 (81.6%) were Xpert-susceptible. No additional RMP-resistant cases were detected using Xpert as compared to phenotypic drug susceptibility testing.

The ability of the Xpert assay to rapidly detect a significantly greater number of bacteriologically confirmed EPTB cases, including RMP-resistant cases, makes it an important diagnostic tool in a TB-endemic country.