Testing multiple different respiratory specimens with Xpert MTB/RIF Ultra (Ultra) provides a novel and useful strategy for rapid diagnosis of pediatric tuberculosis (TB), according to study results published in the American Journal of Respiratory and Critical Care Medicine.1
Diagnosing pulmonary TB in children can be difficult because of nonspecific clinical or radiologic signs and microbiologic confirmation of pulmonary TB is needed to enable timely, effective treatment.
Ultra is a new diagnostic test for TB on the GeneXpert platform that has a substantially lower limit of detection and improved sensitivity compared with Xpert in studies conducted in adults. Therefore, researchers investigated the yield from Ultra on repeated nasopharyngeal aspirate specimens and the use of combinations of induced sputum and nasopharyngeal aspirate specimens to maximize the diagnostic yield in children. They examined 195 South African children hospitalized with suspected pulmonary TB that had one induced sputum and nasopharyngeal aspirate; of these, 130 had 2 nasopharyngeal aspirate specimens.
The researchers documented 40 (20.5%) culture-confirmed cases, and Ultra was positive on nasopharyngeal aspirate specimens in 26 (13.3%) cases and on induced sputum in 31 (15.9%) cases. Sensitivity and specificity of Ultra on one nasopharyngeal aspirate were 46% and 97.9%, respectively, and on one induced sputum were 74.3% and 96.9%, respectively; however, combining one nasopharyngeal aspirate and one induced sputum increased sensitivity to 80%.
“Induced sputum provides a better specimen than repeated nasopharyngeal aspirate for rapid diagnosis using Ultra,” the researchers wrote. “However, Ultra testing of combinations of specimens provides a novel strategy that can be adapted to identify most children with confirmed pulmonary tuberculosis.”
Zar HJ, Workman LJ, Prins M, et al. Tuberculosis diagnosis in children using Xpert Ultra on different respiratory specimens [published on August 5, 2019]. Am J Respir Crit Care Med. doi:10.1164/rccm.201904-0772OC