Tuberculosis Diagnosis in Children Using Xpert Ultra on Different Respiratory Specimens

RATIONALE: Microbiological confirmation of pulmonary tuberculosis in children is desirable.

OBJECTIVES: To investigate the diagnostic accuracy and incremental yield of Xpert-Ultra, a new rapid test, on repeated induced sputum, nasopharyngeal aspirates and combinations of specimens.

METHODS: Consecutive South African children hospitalized with suspected pulmonary tuberculosis were enrolled.

MEASUREMENTS: Induced sputum and nasopharyngeal aspirates were obtained. Nasopharyngeal aspirates were frozen; induced sputum underwent liquid culture, an aliquot was frozen. Ultra was performed on thawed nasopharyngeal aspirates and induced sputum specimens individually. Children were categorised as confirmed, unconfirmed or unlikely tuberculosis according to NIH consensus case definitions. The diagnostic accuracy of Ultra was compared with liquid culture on induced sputum.

MAIN RESULTS: 195 children [median age 23·3 months, 32(16·4%) HIV-infected] had one induced sputum and nasopharyngeal aspirate; 130 had two nasopharyngeal aspirates. There were 40(20·5%) culture confirmed cases. Ultra was positive on nasopharyngeal aspirates in 26(13·3%) and on induced sputum in 31(15·9%). Sensitivity and specificity of Ultra on one nasopharyngeal-aspirate were 46% and 98% respectively, similar by HIV status. Sensitivity and specificity of Ultra on one induced sputum were 74·3% and 96·9% respectively. Combining one nasopharyngeal aspirate and one induced sputum increased sensitivity to 80%. Sensitivity using Ultra on two nasopharyngeal aspirates was 54.2%, increasing to 87.5% with an induced sputum Ultra.

CONCLUSIONS: Induced sputum provides a better specimen than repeated nasopharyngeal aspirate for rapid diagnosis using Ultra. However, Ultra testing of combinations of specimens provides a novel strategy that can be adapted to identify most children with confirmed pulmonary tuberculosis.