ABSTRACT
OBJECTIVES: Early detection of Mycobacterial tuberculosis infection (MTB) is pivotal for the treatment of tuberculosis (TB). BACKGROUND: This study was performed to evaluate the performance of BD ProbeTec ET direct detection assay (DTB) against the gold standard culture technique for confirmation of MTB infection. METHODS: A total of 266 consecutive and non-duplicate clinical specimens for detection of MTB were included in this study. There were 118 respiratory and 148 non-respiratory samples. All samples were tested by microscopy for acid-fast bacillus (AFB), MTB culture and biochemical identification with simultaneous testing by DTB. RESULTS: A total of 88 samples (33%) were culture-positive for MTB including 39/118 respiratory, 29/99 fluid and 20/49 tissue samples. DTB sensitivity for respiratory samples was 97% and specificity was 96% with a positive predictive value (PPV) of 93% and negative predictive value (NPV) of 99%. Sensitivity of DTB in fluid samples was 80%, specificity 88%, PPV 69% and NPV 93% whereas sensitivity of DTB for tissue samples was 25%, specificity 90%, PPV 63% and NPV 63%. Of the 50 (56.8%) smear-positive samples, DTB sensitivity was 100% for respiratory, 85% for fluid and 100% for tissue samples. CONCLUSION: DTB performed within acceptable limits for the rapid detection of MTB in respiratory samples compared to fluid and tissue specimens.
ABSTRACT
OBJECTIVES: 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.
Subject(s)
Bacterial Proteins/genetics , DNA-Directed RNA Polymerases/genetics , Mycobacterium tuberculosis/isolation & purification , Hospitals, Teaching , Humans , Mycobacterium tuberculosis/genetics , Retrospective Studies , Saudi ArabiaABSTRACT
OBJECTIVE: To study the laboratory diagnosis of tuberculosis (TB), and relate the findings to its epidemiology in Central Saudi Arabia. METHODS: This retrospective study was carried out at the Department of Pathology/Microbiology, King Khalid University Hospital, Riyadh, Kingdom of Saudi Arabia between January 2003 and December 2010. Data were retrieved from the hospital information system on laboratory findings. After adjustment, 9,405 specimens were studied. The specimens were stained by Ziehl-Neelsen (ZN), auramine-rhodamine, and cultured in Bactec alert 960, and Lowenstein-Jensen media. Mycobacterium tuberculosis (M. tuberculosis) complex and non-tuberculous mycobacteria were differentiated by ProbTec system and p-nitrobenzoate medium. The BACTEC MGIT 960 SIRE kit was used for susceptibility testing. RESULTS: A total of 568 (6%) specimens grew M. tuberculosis complex, and 87% were from Saudis with an incidence rate of 55.6/100,000 of TB. Time to positive growth in the Bactec liquid medium was directly related to the acid fast bacilli smear load. Most of the positive patients were from the 18-35 years age group. The percentage of multidrug resistance was 0.7%. CONCLUSION: Most patients (87%) were Saudis showing an incident rate of 55.6/100,000. An increase of TB cases was noticed in the 18-35 age group. Resistance to isoniazid was 10.6%, 1% to Rifampicin, 2-8% to Ethambutol, and streptomycin was 6%.
