Rapid detection of Mycobacterium tuberculosis and rifampin-resistance from sputum samples with an easy-to-use PCR test system with near-patient capability

Abstract number: O185

Jones M., Helb D., Story E., Boehme C., Wallace E., Ho K., Kop J., Owens M., Rodgers R., Banada P., Safi H., Blakemore R., Lan N., Jones-López E., Levi M., Burday M., Ayakaka I., Mugerwa R., McMillan B., Winn-Deen E., Christel L., Dailey P., Perkins M., Persing D., Alland D.

Background: Current nucleic acid amplification methods used to detect Mycobacterium tuberculosis are complex, labour-intensive and technically challenging. The Xpert™ MTB real-time PCR assay was developed to overcome these limitations and to rapidly and simultaneously detect M. tuberculosis and rifampin resistance-associated mutations in sputum samples with minimal hands-on effort. Sample processing and real-time nested PCR reactions are integrated in a single, disposable plastic cartridge which contains all of the reagents necessary for sample processing and PCR reactions so that the technician need only add the sample to the cartridge. All steps following sample addition are done automatically on the GeneXpert platform in less than 2 hours.

Objective: The objective was to evaluate the Xpert™ MTB assay sensitivity and specificity for both M. tuberculosis detection and rifampin resistance.

Methods: Analytical studies were performed using sputum spiked with known numbers of M. tuberculosis colony forming units (cfu). Clinical studies were performed with sputum samples from tuberculosis patients in Uganda and Vietnam.

Results: The limit of detection for M. tuberculosis in sputum samples was 131 cfu/mL. As few as ten cfu of M. tuberculosis could be detected in 35% of the samples. All common rifampin-resistance-associated mutations could also be detected. Analysis of samples collected from suspected tuberculosis cases in Vietnam and Uganda showed a sensitivity of 98–100% for smear-positive sputum samples. Sensitivity in smear-negative samples was 84.6% (33/39) when M. tuberculosis was identified by solid media culture, and 71.7% (38/53) when both solid and liquid media were used for identification. Specificity was 100% in all cases. Tests of 64 smear-positive samples collected from retreatment tuberculosis cases in Uganda showed a sensitivity of 100% for detecting rifampin-resistance. Specificity for rifampin-resistance was 98% (63/64), but this rose to 100% after correcting for an error in conventional susceptibility test results.

Conclusions: The Xpert™ MTB Assay is highly effective at detecting smear-positive and smear-negative tuberculosis and rifampin-resistance. This simple-to-use system can perform point-of-care detection of M. tuberculosis directly from sputum in less than two hours.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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