Original Research Article
Year: 2022 | Month: July | Volume: 12 | Issue: 7 | Pages: 312-318
DOI: https://doi.org/10.52403/ijhsr.20220744
Evaluation of GeneXpert MTB/RIF Assay for Rapid Diagnosis of Tuberculosis and Detection of Rifampicin Resistance in Extra Pulmonary Specimens
Sonam Singla1, Smita Sarma1, Sharmila Sengupta2, Sandeep Mittal3, Ashish K Prakash3, Jaiswal A3
1Department of Microbiology, Medanta the Medicity, Gurgaon, Haryana, India
2National center for infectious Diseases,Singapore
3Department of Respiratory & Sleep Medicine, Medanta -The Medicity Gurgaon, India
Corresponding Author: Sonam Singla
ABSTRACT
Introduction: Extra pulmonary tuberculosis (EPTB) accounts for 15%-20% of all tuberculosis (TB) cases. Diagnosis of EPTB is difficult due to its pauci-bacillary nature. The slow growth rate of mycobacterium makes isolation and identification by culture delayed. The Xpert MTB/RIF assay detects both TB and resistance to rifampicin in less than two hours. Hence we compare Gene Xpert with TB culture to diagnose EPTB and determine rifampicin resistance.
Methods: The study was conducted between Nov 2016 to Oct 2017 and all EPTB specimens were collected.The collected specimens were processed for acid fast stain, MTB/RIF assay and liquid culture by MGIT (Mycobacterial Growth Indicator Tube).
Results: A total of 340 EPTB specimens were evaluated. Culture positivity rate was 22.4%. Gene Xpert was positive in 21.7% cases. The sensitivity of Xpert was 68% and specificity was 92% with culture as gold standard. The sensitivity of Gene Xpert in various samples ranged from 93% to 12% being highest in pus sample (93%) and lowest in pleural fluid (13%) whereas the specificity reversed being 100% in pleural fluid and 79% in pus. MTB detected 22 more cases than culture hence Xpert identified 29.7% more cases than culture. We also observed that Xpert missed 9% culture positive cases.
The culture confirmed rifampicin resistant was observed in 12 cases while Gene Xpert identified in 8 among them however in 3 cases Xpert was rifampicin sensitive.
Conclusion: Our study confirms that Xpert MTB/ RIF assay is an important advancement in diagnosing EPTB. Although it cannot replace the conventional techniques but can contribute significantly in an early diagnosis and management of EPTB . Hence a combined approach including acid fast stain, culture identification and sensitivity and Gene Xpert as well as appropriate sample should be sent for an early and reliable diagnosis of EPTB.
Key words: Extra pulmonary tuberculosis, Mycobacterium tuberculosis, Gene Xpert MTB/RIF assay, rifampicin resistance, MGIT (mycobacterial growth indicator tube).