Validity of the GenXpert MTB/RIF in Diagnosis of Pulmonary Tuberculosis & Description of Pulmonary TB Resistance Profile in Abbasia Chest Hospital

Abstract

Background Tuberculosis (TB) is a global public health problem; early diagnosis will enhance the treatment and decrease the resistance to the anti TB drug which improve the overall treatment outcome Objectives Comparing the validity of GeneXpert Mycobacterium tuberculosis /RIF in diagnosing pulmonary TB and detecting Rifampicin resistance with Direct smear microscopy. Subjects& methods Cross sectional study was conducted to collect a sample of 393 clinically suspected cases (January,2016 to February 2018). All cases underwent Direct smear microscopy, GeneXpert (GX) MTB/RIF and Lowenstein– Jensen Cultures Golden standard test for diagnosis of TB and comparing the validity of the two tests. Comparison between GX and the golden standard culture results was done by sensitivity and specificity calculation as well as the Kappa test for agreement between results of tests. Results For 393 clinically suspected TB cases, TB culture confirmed 196 (49.9%) TB positive cases and 197 (50.1%) TB negative cases and 32 Rifampicin resistant cases (16.3%) of the positive TB cases. GX detected 206 (52.4%) TB positive cases and 187(47.6%) TB negative cases and 34 Rifampicin resistant cases. For TB diagnosis, GX sensitivity was 91.8%, specificity was 86.8%, PVP= 87.4%, PVN=91.4Accuracy= 89.3, and substantial agreement between GX and culture as level of agreement =78.6%. As for Rifampicin resistant cases the GX sensitivity =100%, specificity=98.9%, PVP= 94.1%, PVN=98.9%, Accuracy= 99%, and GOOD agreement between GX and culture as kappa = 0.964 (level of agreement is 96.4%). Direct smear microscopy detected 166 (42.2%) TB positive cases and 227(57.8%) TB negative cases. Sensitivity of direct microscopy was 53.6% while specificity was 69%, PVP= 63.3%, PVN=59.9%, Accuracy= 61.3%, and fair agreement between Direct smear microscopy and culture with level of agreement =22.6%. Conclusion GX has the advantage of pulmonary TB rapid testing of high sensitivity and specificity that allows early treatment and decrease of the disease transmission in comparison to the currently used Direct smear microscopy for TB diagnosis