The Xpert MTB/RIF Assay for Diagnosis of Presumptive TB Cases in Taksin Hospital

Abstract

             Tuberculosis (TB) and multi-drug resistant TB (MDR-TB) are a major global health problem, especially in Thailand. The Xpert MTB/RIF molecular test is recommended by WHO for simultaneous detection of Mycobacterium tuberculosis complex (MTB) and rifampicin (RIF) resistance. This research is a retrospective study which aimed to compare the efficiency of the Xpert MTB/RIF test and AFB smear microscopy (Ziehl-Neelsen) with a gold standard TB culture and drug susceptibility testing (TB C&DST). Samples (n = 1,003; 629 males and 374 females) were collected from patients in Taksin Hospital who were presumptive TB cases by clinical manifestation or chest X-ray (CXR) in 2016.  Samples were analyzed by using the Xpert MTB/RIF test, AFB smear microscopy and TB C&DST. The results showed that the prevalence of active TB cases by the Xpert MTB/RIF test was 25.8% (259 specimens), 71.4% (185 specimens) were males and the most prevalence of interval age group was 18-40 years (41.3 %). However, the prevalence by AFB smear microscopy was only 20.9 % (210 specimens). Moreover, the prevalence of risk groups was highest in the elderly/chronic disease group (21.6 %), followed by the HIV-infected (13.9 %) and diabetes mellitus (11.6) groups. Furthermore, the most prevalence of rifampicin resistance and MDR-TB were observed in the HIV-infected group. Efficiency of the Xpert MTB/RIF test and AFB smear microscopy were then compared with the gold standard TB C&DST. The  results showed sensitivity, specificity, PPV, NPV and accuracy of the Xpert MTB/RIF test at 97.4, 89.2, 90.5, 97.1 and 93.4 %, respectively and the rifampicin resistant MTB detection at 85.7, 98.2, 80.0, 98.8 and 97.2%, respectively. When AFB smear microscopy was negative, the % sensitivity, specificity, PPV, NPV and accuracy of the Xpert MTB/RIF test were 84.9, 92.7, 70.0, 96.8 and 91.4%, respectively, and that of AFB smear microscopy were 83.1, 88.7, 88.5, 83.3 and 85.8%, respectively. Therefore, AFB smear microscopy could detect MTB at a significantly lower efficiency than that  by the Xpert MTB/RIF test (p <0.05, χ² test). In conclusion, the Xpert MTB/RIF test is an easy, rapid and highly efficient test for MTB and rifampicin resistance detection, especially in the AFB smear negative cases. Therefore, it could be used as an effective method for TB diagnosis.