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

Huttaya Thuncharoon


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 (RIP) resistance. This research  is a retrospective study  which aimed  to compare  the efficiency  of the Xpert MTB/RIF test and AFB smear microscopy (Ziehi-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/ RIP  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,  x2  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.

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