Diagnostic validation of rapid molecular detection of Mycobacterium tuberculosis in pus samples by GeneXpert

Abstract

Objective: To evaluate the performance of GeneXpert for detection of mycobacterium tuberculosis in pus samples and compare its results with conventional techniques in terms of validity, rapidity and rifampicin resistance.

Methods: This longitudinal, descriptive study was conducted at Jinnah Hospital, Lahore, Pakistan, from January 2012 to December 2015, and comprised pus samples of people suspected of having extra-pulmonary tuberculosis. Participants were included by using consecutive sampling technique. The pus samples were subjected to Ziehl-Neelsen smear microscopy and Lowenstein-Jensen culture as per World Health Organisation's protocol and GeneXpert as per manufacturer protocol. SPSS 17 was used for data analysis. Validity of GeneXpert and rifampicin resistance were determined and compared with Ziehl-Neelsen staining using Lowenstein-Jensen culture as the gold standard.

Results: Of the 212 pus samples, 84(39.6%) were positive on Lowenstein-Jensen culture with mean turnaround time of 20±6 days, 77(36.3%) on GeneXpert and 22(10.4%) on Ziehl-Neelsen smear. The highest detection rate of mycobacterium tuberculosis 62(80.5%) was in lymph node samples by GeneXpert. The sensitivity and specificity of GeneXpert were 91.6% and 100% respectively, while Ziehl-Neelsen smear showed a sensitivity26.2% and specificity of 100%. Rifampicin resistance was detected in 5(6.4%) pus samples by GeneXpert.

Conclusions: GeneXpert had a higher validity compared to Ziehl-Neelsen smear microscopy.

Keywords: Mycobacterium tuberculosis (MTB), Lowenstein-Jensen (LJ) culture, Pulmonary tuberculosis (PTB), Ziehl-Neelsen (ZN) stain..