Abstract

Global Mycobacterium tuberculosis (MTB) control efforts have been severely hampered by the lack of diagnostic tests that are accurate, simple to use and can be applied at the point of clinical care. This compounded by the widespread inability to test for drug resistance. The newly developed Xpert MTB/RIF assay utilizes real-time PCR technology to both diagnose TB and detect rifampicin (RIF) resistance concurrently using unprocessed clinical specimens, regardless of their smear status. The study was designed to assess the diagnostic accuracy of Xpert MTB/RIF assay in detecting MTB and MDR-TB in comparison to the conventional methods in a sample of MTB Egyptian patients. Forty (40) sputum specimens were collected from adult patients having pulmonary tuberculosis from Chest hospital, Egypt. Ten (10) external control patients were enrolled. The conventional method, including Ziehl-Neelsen staining showed the presence of MTB in 77.5% and bacterial culture in 85%. Whereas, the Xpert MTB/RIF test provided detection of 82.5%, in addition it correctly identified five out of six cases of RIF resistant MTB with sensitivity and specificity (83 and 100%) respectively, the resistant cases were all previously treated with RIF. Sensitivity, specificity, positive and negative predictive value of Xpert MTB/RIF in comparison to conventional culture was 97.14, 100, 100 and 85.7%, respectively. The control group showed no positive results with the Xpert MTB/RIF. The sensitivity of Xpert for smear positive, culture positive TB was 100% and in smear negative, culture positive TB was 66.6% while its specificity in both was 100%. Comparing processed and unprocessed samples, the sensitivity of Xpert MTB/RIF was 94 and 97%, respectively while its specificity was 100% in both conditions. Thus, Xpert MTB /RIF outperformed smear microscopy, establishing a diagnosis in a proportion of patients with smear negative MTB, which detected many highly likely MTB by culture, and accurately ruled out rifampicin resistant TB.

Key words: Multi Drug Resistance Tuberculosis (MDR-TB), polymerase chain reaction (PCR), Mycobacteruim tuberculosis (MTB), extensively drug-resistant TB (XDR-TB).