Comparison of Xpert MTB/RIFAssay with smear microscopy and culture for the detection of pulmonary tuberculosis

Abstract

Tuberculosis (TB) remains one of the world’s most serious diseases, leading to more than one million deaths each year. The emergence of drug-resistant strains of Mycobacterium tuberculosis poses a threat to tuberculosis control programs and often results in high-level of mortality. Current methods of detection and determining anti-mycobacterial susceptibility are time consuming. Xpert MTB/RIF assay, used in this study, is an automated real-time polymerase chain reaction (PCR) system with rapid on-demand, near-patient technology, which can simultaneously detect M. tuberculosis and rifampicin resistance status within two hours. In this study we used 145 sputum specimens from suspected TB patients. All specimens were tested by AFB microscopy, Xpert MTB/RIF assay and conventional culture. Culture positive specimens were further tested for drug susceptibility testing (DST) against four first line anti-TB drugs. Among 145 sputum specimens 20 (13.80%) were positive in AFB microscopy. Among 20 AFB positive cases 8 (40%) were scanty, 3 (15%) were 3+, 4 (10%) were 2+ and 5 (25%) were 1+ respectively. Among 28 GeneXpert positive cases, 5 (17.85%) were very low, 10 (35.71%) were low, 8 (28.57%) were medium, 5 (17.85%) were high detection level respectively. Two isolates were found to be rifampicin resistant in Xpert MTB/RIF assay test. Among the 23 culture positive cases, DST results were available for 20 cases of which 19 were sensitive to all drugs while the remaining 1 was resistant to Isoniazid, Rifampicin and Streptomycin. Between Xpert MTB/RIF assay and smear microscopy sensitivity and speicficity were 100%, Xpert MTB/RIF assay were compared with the conventional culture on LJ media, sensitivity and specificity were 82.61% and 92.62% respectively and smear microscopy were compared with the culture, sensitivity and specificity were 65.22% and 95.90% respectively. From this data we can conclude that Xpert MTB/RIF assay is more useful then other conventional methods.