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Rapid, Automated Test Accurately Detects Tuberculosis in Pediatric Samples

By BiotechDaily International staff writers
Posted on 08 Aug 2013
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Image: The Xpert MTB/RIF test cartridge (Photo courtesy of Cepheid).
Image: The Xpert MTB/RIF test cartridge (Photo courtesy of Cepheid).
Image: The GeneXpert System loaded with a test cartridge (Photo courtesy of Cepheid).
Image: The GeneXpert System loaded with a test cartridge (Photo courtesy of Cepheid).
A team of South African investigators compared the effectiveness of a new, automated diagnostic test that simultaneously detects tuberculosis (TB) and rifampicin resistance to classical microscopy and culture methods in pediatric samples.

The World Health Organization (WHO) estimated that in 2011 alone more than 500,000 new cases of TB appeared with nearly 64,000 deaths among those younger than 15 years of age.

The authors of the current study collected nearly 1,500 paired sputum and nasopharyngeal specimens from 354 children who presented at a primary care clinic with symptoms of TB. The samples were analyzed with the Cepheid (Sunnyvale, CA, USA; www.cepheidinternational.com) Xpert MTB/RIF test, and the diagnostic accuracy of the results were compared with the reference standards of culture and smear microscopy.

The Xpert MTB/RIF Test detects both TB and rifampicin resistance high sensitivity even in smear negative, culture positive specimens. The test produces results in two hours and requires no instrumentation other than the GeneXpert System.

Cepheid's GeneXpert System is a closed, self-contained, fully integrated, and automated platform that combines on-board sample preparation with real-time PCR (polymerase chain reaction) amplification and detection functions for fully integrated and automated nucleic acid analysis. The system is designed to purify, concentrate, detect, and identify targeted nucleic acid sequences thereby delivering answers directly from unprocessed samples.

Results revealed that five children (1%) tested positive for tuberculosis by smear microscopy, 26 (7%) tested positive by Xpert MTB/RIF, and 30 (8%) tested positive by culture. Among children who did not in fact have the disease, the results of the Xpert test reported negative for TB with 99% accuracy. These findings suggest that Xpert MTB/RIF on respiratory secretions is a useful test for rapid diagnosis of pediatric pulmonary tuberculosis in primary care.

Dr. Fred Tenover, senior director of scientific affairs at Cepheid, said, "If you were to inoculate an Xpert MTB/RIF test at the same time you started preparing your acid fast smears, by the time you finished reading the smears, the Xpert MTB/RIF test result would be ready, telling you if your positive acid fast smear was TB and if the strain was resistant to rifampicin, which is an excellent surrogate marker for MDR (multiple drug resistant)-TB. I am sure Koch and Pasteur would not only be delighted with the technological advance, they would probably say, 'It is about time.'"

“There has been a perception amongst health care workers that rapid diagnosis of TB in children would not be possible in primary care, but this study disproves that view, said first author Dr. Heather Zar, professor of pediatrics at the University of Cape Town (South Africa; www.scah.uct.ac.za). “Given our results, widespread adoption of rapid testing for TB and drug resistance in children may substantially improve public health without greatly increasing costs.”

Results of the South African study were published in the August 2013 issue of the journal the Lancet Global Health.

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University of Cape Town

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