The Role of Xpert MTB/RIF Ultra in Diagnosing Pulmonary Tuberculosis in Children

Schaaf and Marais discuss the study by Zar and colleagues on the value of the new Xpert MTB/RIF Ultra (Ultra) in hospitalized children suspected of having pulmonary tuberculosis. Ultra on one induced sputum (IS) and one or two nasopharyngeal aspirates (NPAs) were compared with mycobacterial culture from a single IS specimen. Compared with culture, Ultra yield from a single IS specimen (74.3%) was much better than from two NPA specimens (54.2%), but multiple specimens provided the best sensitivity: 87% for single IS plus two NPAs. The authors stress the fact that Ultra yield may have been compromised by storage of the original specimens before testing, but DNA is robust, and the expected detrimental effect of freezing at −80°C is minimal. Even if there were some detrimental effects, the results presented represent an underestimation, rather than an overestimation, of the true diagnostic performance using fresh specimens.