Background: Diagnosis of abdominal tuberculosis (TB) from ascitic fluid samples using routinely available diagnostic methods is challenging due to its paucibacillary nature. Although performance of Xpert MTB/RIF assay has been evaluated extensively on pulmonary samples, its performance on extrapulmonary samples is still under evaluation.
Objectives: The objective of this study was to find out the performance of Xpert MTB/RIF on ascitic fluid samples obtained from suspected cases of abdominal TB. Performance was compared with Mycobacterium growth indicator tube-960 (MGIT-960) culture and in-house multiplex polymerase chain reaction (PCR). The latter detects and differentiates Mycobacterium tuberculosis and nontuberculous mycobacteria simultaneously.
Materials and methods: Sixty-seven patients suspected of probable/possible abdominal TB were included in this observational, prospective study. All samples were tested by Ziehl-Neelsen staining, MGIT-960 culture, in-house multiplex PCR, and Xpert MTB/RIF assay.
Results: All 67 samples were smear negative. Seventeen (25.4%) were MGIT-960 culture positive while 12 (17.9%) were detected positive by the Xpert MTB/RIF assay and 9 (13.4%) by in-house multiplex PCR. Sensitivity and specificity of the Xpert MTB/RIF assay compared with the MGIT-960 culture were 70.6% (95%, confidence interval [CI]: 44.1-89.7) and 100% (95%, CI: 92.8-100) and that of in-house multiplex PCR were 52.9% (95%, CI: 30.9-73.8) and 100% (95%, CI: 92.8-100), respectively.
Conclusions: Diagnostic yield of Xpert MTB/RIF assay on ascitic fluid samples was lower than MGIT-960 culture. We thus emphasize on the need for urgent discovery of new biomarkers for paucibacillary TB.
Keywords: Abdominal tuberculosis; Mycobacterium growth indicator tube-960 culture; Xpert MTB/RIF; ascitic fluid; multiplex polymerase chain reaction.