Rapid diagnosis of tuberculosis using Xpert MTB/RIF assay - Report from a third world country

Objective: To evaluate the diagnostic accuracy of the Xpert MTB/RIF assay for the detection of M. tuberculosis in pulmonary and extrapulmonary specimens and to compare it with conventional techniques.

Methods: During a period of 10 months from December 2012 through September 2013, two hundred and forty five clinically TB suspects were enrolled for Xpert MTB\RIF assay. The cohort comprised of 205 suspects of pulmonary TB and 40 of extrapulmonary TB (EPTB). The 40 EPTB samples included pus aspirated from different sites of the body (n=19), pleural fluid (n=11), ascitic fluid (n=7), pericardial fluid, CSF and urine one each. Ziehl-Neelsen (ZN) Stained smear microscopy, culture on LJ media and Xpert MTB/RIF assay was performed on samples from these patients.

Results: M. tuberculosis (MTB) were detected by Xpert MTB/RIF test in 111 (45.3%) out of 245 samples. Of these, 85 (34.7%) were smear positive on ZN staining and 102 (41.6%) were positive on LJ cultures. Rifampicin resistance was detected in 16 (6.5%) patients. Nine out of 19 pus samples (47.3%) were positive for MTB by Gene Xpert, 03 (15.8%) on ZN staining and 04 (21%) on LJ culture. MTB could not be detected in any other extrapulmonary sample.

Conclusion: Xpert MTB/RIF is a sensitive method for rapid diagnosis of Tuberculosis, especially in smear negative cases and in EPTB as compared to the conventional ZN staining. Among EPTB cases the highest yield of positivity was shown in Pus samples. For countries endemic for TB GeneXpert can serve as a sensitive and time saving diagnostic modality for pulmonary and EPTB.