Novel specimens feasible and sensitive for Xpert® MTB/RIF diagnosis in children

Performance of Xpert® MTB/RIF and alternative specimen collection methods for the diagnosis of tuberculosis in HIV-infected children.

Marcy O, Ung V, Goyet S, Borand L, Msellati P, Tejiokem M, Nguyen Thi NL, Nacro B, Cheng S, Eyangoh S, Pham TH, Ouedraogo AS, Tarantola A, Godreuil S, Blanche S, Delacourt C, PAANTHER study group. Clin Infect Dis. 2016 Feb 7. pii: ciw036. [Epub ahead of print]

Methods: HIV-infected children aged 13 years with suspected intrathoracic tuberculosis were enrolled in 8 hospitals in Burkina Faso, Cambodia, Cameroon, and Vietnam. Gastric aspirates were taken for children aged <10 years and expectorated sputum samples were taken for children aged 10 years (standard samples); nasopharyngeal aspirate and stool were taken for all children, and a string test was performed if the child was aged 4 years (alternative samples). All samples were tested with Xpert®. The diagnostic accuracy of Xpert® for culture-confirmed tuberculosis was analyzed in intention-to-diagnose and per-protocol approaches.

Results: Of 281 children enrolled, 272 (96.8%) had ≥1 specimen tested with Xpert® (intention-to-diagnose population), and 179 (63.5%) had all samples tested with Xpert® (per-protocol population). Tuberculosis was culture-confirmed in 29/272 (10.7%) children. Intention-to-diagnose sensitivities of Xpert® performed on all, standard, and alternative samples were 79.3% (95% confidence interval [CI], 60.3-92.0), 72.4% (95% CI, 52.8-87.3), and 75.9% (95% CI, 56.5-89.7), respectively. Specificities were 97.5%. Xpert® combined on nasopharyngeal aspirate and stool had intention-to-diagnose and per-protocol sensitivities of 75.9% (95% CI, 56.5-89.7) and 75.0% (95% CI, 47.6-92.7), respectively.

Conclusions: The combination of nasopharyngeal aspirate and stool sample is a promising alternative to methods usually recommended by national programs. Xpert® performed on respiratory and stools samples enables rapid confirmation of tuberculosis diagnosis in HIV-infected children.

Abstract access   [1]

Editor’s notes: This article reports on a prospective cohort study of HIV-positive children (≤ 13 years) with suspected intrathoracic tuberculosis in eight hospitals in Burkina Faso, Cambodia, Cameroon, and Viet Nam. Diagnosis of tuberculosis among children is challenging because it is more difficult to obtain sputum, and their sputum often has fewer bacilli, requiring more sensitive tests. In 2014, WHO recommended scaling-up the use of Xpert® MTB/RIF among children. However, any test which is dependent on obtaining a sputum specimen will be suboptimal for diagnosis of tuberculosis in children.

In this study the investigators examined the feasibility of using alternative specimens with Xpert® MTB/ RIF for the diagnosis of tuberculosis in HIV-positive children. Using an intention-to-diagnose and a per-protocol analysis, they also assessed the diagnostic accuracy of Xpert® on nasopharyngeal aspirate and stool samples, using culture-confirmed tuberculosis as the reference standard.

The authors found that the performance of Xpert® in alternative samples was comparable to that of standard samples. They found excellent feasibility of obtaining samples of nasopharyngeal aspirates and stool, and a good sensitivity of Xpert® (~76%) when using that combination of samples. The authors suggested more research to simplify the processing of the stool samples for Xpert®, which would make the combination of both samples an attractive collection method for children unable to produce sputum.

Although Xpert® produces results relatively rapidly, some testing was done retrospectively, and only half of the Xpert® results were immediately available. As many children in this study had features of severe disease, it is not surprising that clinicians often started TB treatment immediately without waiting for results. Thus in practice the Xpert® result often provided bacteriological confirmation of a clinical diagnosis for children who had already started TB treatment, although it did also lead to some TB treatment initiations.

Despite conducting this study over more than two years in eight hospitals, the final number of enrolled children with culture-confirmed tuberculosis was only 29. It would be interesting to know whether using Xpert® on alternative specimens from children had an impact on patient-important outcomes, particularly mortality, though this would have required a much larger study. Studies of Xpert® implementation among adults have found increased yield in terms of bacteriological diagnoses. However, most have not found an impact on patient-important outcomes. Several children died before all the protocol-required specimens could be obtained, emphasizing the importance of rapid and more sensitive TB diagnostic tests for severely-ill children.

Africa [7], Asia [8]
Burkina Faso [9], Cambodia [10], Cameroon [11], Viet Nam [12]
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