Medical Xpress (07.25.2013)
Aids Weekly Plus
A new test called Xpert MTB/RIF detected approximately two thirds of TB cases found by the current culture test in significantly less time. Generally, a preliminary diagnosis requires the examination of a sample of lung secretions under a microscope to determine if it contains TB bacteria. In addition, a sample is sent to a laboratory to be cultured and identified; a lab culture test can take as long as six weeks to show a positive result. Children have less infectious bacteria than adults, which increases the level of difficulty in detecting the bacteria under a microscope or growing a culture.
In a study sponsored by the US National Institutes of Health (NIH), researchers in South Africa collected approximately 1,500 samples from approximately 400 children who presented at a primary care clinic with TB symptoms. Trained clinical staff with special equipment collected samples of secretions from the children’s lungs, nasal passages, or both. The researchers compared results from the Xpert MTB/RIF test with the microscope detection test and laboratory culture test. Of the 30 TB cases detected by culture, the Xpert test diagnosed 19 (63 percent) positive cases while microscopic examination only detected 4 cases (13 percent). Adding a second test with additional samples improved detection rate for both tests.
Xpert MTB/RIF results were available in an average of 24 hours compared with more than two weeks for the culture test. Results indicated that ease and timeliness of diagnosis with the Xpert MTB/RIF were important for clinics in resource-limited countries where equipment for traditional tests might not be available. The test also identified strains of TB resistant to rifampicin, which helped clinicians determine the right treatment. This is particularly important for countries where drug-resistant strains are common. The Xpert MTB/RIF test was 99-percent accurate in identifying children who did not have TB.
NIH’s National Institute of Allergy and Infectious Diseases funded the development of the Xpert MTB/RIF test and the National Institute of Child Health and Human Development funded the Xpert MTB/RIF testing examined by this study.
The full report, “Rapid Diagnosis of Pulmonary Tuberculosis in African Children in a Primary Care Setting by Use of Xpert MTB/RIF on Respiratory Specimens: A Prospective Study,” was published online in the journal Lancet Global Health (2013; doi:10.1016/S2214-109X(13)70036-6).