title: Evaluation of GeneXpert MTB/RIF for detection of Mycobacterium tuberculosis complex and rpo B gene in respiratory and non-respiratory clinical specimens at a tertiary care teaching hospital in Saudi Arabia.
abstract: To assess the performance of Xpert MTB/RIF, an automated molecular test for Mycobacterium tuberculosis (MTB) and resistance to rifampin (RIF), against smear microscopy and culture method for diagnosis of MTB infection. Methods: This is a retrospective analysis of 103 respiratory and 137 non-respiratory patient specimens suspected of tuberculosis at King Khalid University Hospital, Riyadh, Kingdom of Saudi Arabia performed between April 2014 and March 2015. Each sample underwent smear microscopy, mycobacterial culture, and GeneXpert MTB/RIF test. Results: Fifteen out of 103 respiratory samples were smear and culture positive, whereas 9 out of 137 non-respiratory samples were smear positive. Out of 9 smear positive specimens, 8 were also culture positive. All 15 culture positive respiratory samples were detected by Xpert MTB/RIF (sensitivity  and positive predictive value [PPV]=100%). Similarly, all 8 culture positive non-respiratory specimens were identified by Xpert MTB/RIF (sensitivity 100%; PPV 88.8%). The Xpert MTB/RIF detected only one false positive result in 88 smear negative respiratory specimens (specificity 98.9%; negative predictive value [NPV]= 100%). All 125 smear negative non-respiratory specimens tested negative by culture and Xpert MTB/RIF (sensitivity, specificity, PPV, NPV= 100%). Conclusion: The performance of Xpert MTB/RIF was comparable to the gold standard culture method for identification of MTB in both respiratory and non-respiratory clinical specimens.
authors.affiliation: Department of Pathology/Microbiology, College of Medicine, King Khalid University Hospital, King Saud University, Riyadh, Kingdom of Saudi Arabia. E-mail. ali.somily@gmail.com.
authors.forename: Ali M
authors.initials: AM
authors.lastname: Somily
authors.forename: Mazin A
authors.initials: MA
authors.lastname: Barry
authors.forename: Hanan A
authors.initials: HA
authors.lastname: Habib
authors.forename: Fawzia E
authors.initials: FE
authors.lastname: Alotaibi
authors.forename: Fahad A
authors.initials: FA
authors.lastname: Al-Zamil
authors.forename: Mohammed A
authors.initials: MA
authors.lastname: Khan
authors.forename: Mohammed S
authors.initials: MS
authors.lastname: Sarwar
authors.forename: Nawab D
authors.initials: ND
authors.lastname: Bakhash
authors.forename: Abdulkarim A
authors.initials: AA
authors.lastname: Alrabiaah
authors.forename: Zahid A
authors.initials: ZA
authors.lastname: Shakoor
authors.forename: Abiola C
authors.initials: AC
authors.lastname: Senok
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D012321:DNA-Directed RNA Polymerases / Q000235:genetics*; D006784:Hospitals, Teaching; D006801:Humans; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000302:isolation & purification*; D012189:Retrospective Studies; D012529:Saudi Arabia
chemical_list: D001426:Bacterial Proteins; C505805:rpoB protein, Mycobacterium tuberculosis; D012321:DNA-Directed RNA Polymerases