July 2018
by Lindsay McKenna
Existing tests and those under development that are designed to detect tuberculosis (TB) bacteria (see the Tuberculosis Diagnosis Pipeline, coming soon) are suboptimal for children, who often have fewer TB bacteria in their bodies than adults (paucibacillary disease). The usefulness of sputum-based tests is limited in young children, who often experience difficulty producing sputum and have high rates of extrapulmonary TB. Even using the gold standard of culture, microbiological confirmation of TB is obtained in only 15–20 percent of children with clinically diagnosed TB.
Testing and optimizing the performance of existing tests in children remains important, and efforts are underway, including evaluating the performance of nucleic-acid amplification tests (i.e., Xpert MTB/RIF) on sample types other than sputum and antigen-based tests in children. The new Xpert Ultra assay is expected to have improved sensitivity in all sample types. But to radically improve rates of diagnosis in children with TB, a rapid diagnostic test that is not sputum or pathogen based, and is instead dependent on easier-to-obtain samples and the host’s response to TB, may be required.
Considering age-dependent differences in the immune response to TB, and the broad spectrum of TB disease observed in children, the TB diagnostics research community and funders need to join the drug development community in accepting that “children are not just small adults.” There is an urgent need to scale up pediatric-specific discovery, validation, and implementation research efforts to develop novel assays that can detect TB antigens, host markers, or gene signatures (genes differentially expressed under certain biological or other conditions, for example, in the presence of TB infection or disease) in children.
The following table provides information on promising non-sputum pathogen detection approaches, antigen-based assays, host marker-based assays, and gene signatures that are in development and undergoing evaluation for use in children.
Table 1. Assays and Gene-Signatures Under Evaluation for the Detection of TB Infection and Disease in Children
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Assay Name |
Signature/ Biomarker and Indication |
Company/ Sponsor(s) |
Location(s) of Pediatric Study Cohorts |
Status |
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Xpert MTB/RIF on stool |
Mycobacterium tuberculosis (MTB) complex in stool
For detecting TB disease in children |
Cepheid |
Burkina Faso, Cambodia, Cameroon, Kenya, Pakistan, South Africa, Uganda, Vietnam, Zimbabwe |
WHO guidance issued in 2013; data available on the utility of Xpert on stool were limited and not considered in the analysis |
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Pediatric studies of Xpert MTB/RIF on stool samples compared to those on sputum or gastric aspirate samples report sensitivities of 32–90 percent with specificities of 97–100 percent. Sensitivity was higher in HIV-positive children and among children who were hospitalized or with more severe disease. Xpert MTB/RIF on stool samples may have potential value as a rule-in test to aid early TB diagnosis in children.
Sample processing methods are being explored to optimize the use of Xpert MTB/RIF on stool for diagnosing TB in children. Larger clinical studies are needed to validate these methods and their impact on the sensitivity and specificity of Xpert MTB/RIF on stool. A new stool processing kit designed to be used in conjunction with Xpert MTB/RIF is being developed by the Foundation for Innovative Diagnostics (FIND) and Rutgers University.
LaCourse SM, Pavlinac PB, Cranmer LM, et al. Stool Xpert MTB/RIF and urine lipoarabinomannan for the diagnosis of tuberculosis in hospitalized HIV-infected children. AIDS 2018 Jan 2;32(1):69-78. doi: 10.1097/QAD.0000000000001662.
Orikiriza P, Nansumba M, Nyehangane D, et al. Xpert MTB/RIF diagnosis of childhood tuberculosis from sputum and stool samples in a high TB-HIV-prevalent setting. Eur J Clin Microbiol Infect Dis. 2018 May 8. doi: 10.1007/s10096-018-3272-0. [Epub ahead of print]
Hasan Z, Shakoor S, Arif F, et al. Evaluation of Xpert MTB/RIF testing for rapids diagnosis of childhood pulmonary tuberculosis in children by Xpert MTB/RIF testing of stool samples in low resource settings. BMC Res Notes. 2017 Sep 8;10(1):473. doi: 10.1186/s13104-017-2806-3.
Walters E, van der Zalm MM, Palmer M, et al. Xpert MTB/RIF on stool is useful for the rapid diagnosis of tuberculosis in young children with severe pulmonary disease. Pediatr Infect Dis J. 2017 Sep;36(9): 837-43. doi: 10.1097/INF.0000000000001563. Chipinduro M, Mateveke K, Makamure B, et al. Stool Xpert MTB/RIF test for the diagnosis of childhood pulmonary tuberculosis in primary clinics in Zimbabwe. Int J Tuberc Lung Dis. 2017 Feb 1;21(2):161-6. doi: 10.5588/ijtld.16.0357.
Marcy O, Ung V, Goyet L, et al. Performance of Xpert MTB/RIF and alternative specimen collection methods for the diagnosis of tuberculosis in HIV-infected children. Clin Infect Dis. 2016 May 1;62(9):1161-8. doi: https://doi.org/10.1093/cid/ciw036. Banada PB, Naidoo U, Deshpande S, et al. A novel sample processing method for rapid detection of tuberculosis in the stool of pediatric patients using the Xpert MTB/RIF Assay. PLoS One. 2016 Mar 23;11(3):e0151980. doi: 10.137/journal.pone.0151980.
Policy Update: Automated real-time nucleic acid amplification technology for rapid and simultaneous detection of tuberculosis and rifampin resistance: Xpert MTB/RIF assay for the diagnosis of pulmonary and extrapulmonary TB in adults and children. Geneva: World Health Organization; 2013. |
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Xpert MTB/RIF on nasopharyngeal aspirates (NPAs) |
Mycobacterium tuberculosis (MTB) complex in NPAs
For detecting TB disease in children |
Cepheid |
Burkina Faso, Cambodia, Cameroon, South Africa, Vietnam |
WHO guidance issued in 2013; data available on the utility of Xpert MTB/RIF on NPAs were too limited |
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A pediatric study of Xpert MTB/RIF on repeat NPAs compared to culture on NPA or induced sputum reported 65 percent sensitivity (71 percent for Xpert MTB/RIF on induced sputum) and 98.2 percent specificity (99.1 percent for Xpert MTB/RIF on induced sputum). Xpert MTB/RIF testing on a second NPA produced a 36.7 percent increase in yield, suggesting the utility of Xpert MTB/RIF on repeat NPAs in settings where, or in children for whom, induced sputum or culture is not feasible.
A pediatric study of Xpert MTB/RIF on NPAs only and NPAs plus stool compared to culture in HIV-positive children reported 62.5 percent and 75.0 percent sensitivity and 100.0 percent and 99.4 percent specificity, respectively (on standard samples [sputum or gastric aspirate] Xpert MTB/RIF demonstrated 81.3 percent sensitivity and 98.2 percent specificity). These findings suggest the potential utility of combinations of alternative samples that are easier to collect for diagnosing TB in children.
Marcy O, Ung V, Goyet L, et al. Performance of Xpert MTB/RIF and alternative specimen collection methods for the diagnosis of tuberculosis in HIV-infected children. Clin Infect Dis. 2016 May 1;62(9):1161-8. doi: 10.1093/cid/ciw036.
Zar HJ, Workman L, Isaacs W, et al. Rapid molecular diagnosis of pulmonary tuberculosis in children using nasopharyngeal specimens. Clin Infect Dis. 2012 Oct;55(8):1088-95. doi: 10.1093/cid/cis598.
Policy Update: Automated real-time nucleic acid amplification technology for rapid and simultaneous detection of tuberculosis and rifampin resistance: Xpert MTB/RIF assay for the diagnosis of pulmonary and extrapulmonary TB in adults and children. Geneva: World Health Organization; 2013. |
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Determine TB LAM Ag urine test |
TB antigen lipoarabinomannan (LAM)
For detecting TB disease in children living with HIV |
Alere (Abbott) |
Kenya, South Africa |
WHO guidance issued in 2015 |
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The Determine TB LAM Ag urine test has low sensitivity (50 percent compared to culture and 63 percent compared to Xpert in HIV-positive children) for diagnosing TB in children but predicts mortality among HIV-positive children with unconfirmed TB. Urine-based LAM assays may have potential value as a rule-in test to aid early TB diagnosis in HIV-positive children.
LaCourse SM, Cranmer LM, Njuguna IN, et al. Urine tuberculosis lipoarabinomannan predicts mortality in hospitalized human immunodeficiency virus-infected children. CID. 2018 May 17;66(11):1798-1801. doi: 10.1093/cid/ciy011.
LaCourse SM, Pavlinac PB, Cranmer LM, et al. Stool Xpert MTB/RIF and urine lipoarabinomannan for the diagnosis of tuberculosis in hospitalized HIV-infected children. AIDS. 2018 Jan 2;32(1):69-78. doi: 10.1097/QAD.0000000000001662.
Policy Guidance: the use of lateral flow urine lipoarabinomannan assay (LF-LAM) for the diagnosis and screening of active tuberculosis in people living with HIV. Geneva: World Health Organization; 2015. |
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C-Tb skin test |
TB antigens ESAT-6 and CFP10
For determining TB infection in children |
The Statens Serum Institute |
South Africa, Spain |
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C-Tb, TST, and interferon-gamma release assays (IGRAs) performed equally well at determining TB infection in children, but low CD4+ T-cell counts (<100 cells/mm3) may reduce C-Tb test performance.
Ruhwald M, Aggerbeck H, Vazquez Gallardo R, et al. Safety and efficacy of the C-Tb skin test to diagnose Mycobacterium tuberculosis infection, compared with an interferon release assay and the tuberculin skin test: a phase 3, double-blind, randomized, controlled trial. Lancet Respir Med. 2017 Apr;5(4):259–268. doi: 10.1016/S2213-2600(16)30436-2.
Ruhwald M, Cayla J, Aggerbeck H, et al. Diagnostic accuracy of C-Tb skin test for LTBI: results from two phase III trials [OA-357-27]. Oral abstract presented at: 47th Union Conference. 2016 October 27; Liverpool, UK. Available from: http://www.professionalabstracts.com/union2016/iplanner/#/grid. |
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TAM-TB blood test |
T-cell activation markers
For detecting TB disease in children |
University Hospital, LMU (University of Munich); German Center for Infection Research (DZIF) |
Tanzania |
Undergoing further development and evaluation |
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Compared to culture, the TAM-TB assay demonstrated 83 percent sensitivity among children with culture-confirmed TB and 96.8 percent specificity among children classified as not having TB. The sensitivity of the TAM-TB assay was 69 percent when children with highly probable TB were included alongside those with culture confirmed TB. Encouragingly, positivity rates decreased with decreasing clinical diagnostic certainty.
Portevin D, Moukambi F, Clowes P, et al. Assessment of the novel T-cell activation marker-tuberculosis assay for diagnosis of active tuberculosis in children: a prospective proof-of-concept study. Lancet Infect Dis. 2014 Oct;14(10):931-8. doi: 10.1016/S1473-3099(14)70884-9. |
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Kaforou et al. three-gene signature |
Unpublished; includes GBP5
For distinguishing TB disease from other diseases and from TB infection in children |
Imperial College London
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Kenya, Malawi, South Africa |
Undergoing further development and evaluation |
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The Kaforou et al. three-gene signature (derived from the 51-gene signature identified by Anderson et al.) demonstrated 93.3 percent sensitivity and 80 percent specificity in pediatric test data sets from South Africa and Malawi, and 95.5 percent sensitivity and 73.1 percent specificity in a pediatric validation data set from Kenya.
Kaforou M. Host bio-signatures for TB diagnosis: analytical challenges and future directions. Symposium presentation at: 47th Union Conference. 2016 October 29; Liverpool, UK. Available from: http://www.professionalabstracts.com/union2016/iplanner/#/grid.
Anderson ST, Kaforou M, Phil M, et al. Diagnosis of childhood tuberculosis and host RNA expression in Africa. N Engl J Med. 2014 May 1;370(18):1712-1723. doi: 10.1056/NEJMoa1303657. |
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Sweeney et al. three-gene signature |
GBP5, DUSP3, and KLF2 For distinguishing TB infection from TB disease in children |
Stanford Institute for Immunity, Transplantation and Infection |
Kenya, Malawi, South Africa, Venezuela |
Undergoing further development and evaluation |
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The Sweeney et al. three-gene signature could distinguish TB infection from culture-positive TB disease in children with 86 percent sensitivity and specificity, but TB scores (calculated by subtracting the mean expression of downregulated genes from the mean expression of upregulated genes) in children with culture-negative TB were significantly lower than those in children with culture-positive TB, suggesting lower sensitivity in children with culture-negative TB or incorrect classification of children with other diseases as having culture-negative TB. Sweeney TE, Braviak L, Tato CM, et al. Genome-wide expression for diagnosis of pulmonary tuberculosis: a multicohort analysis. Lancet Respir Med. 2016 Mar;4(3):213-24. doi: 10.1016/S2213-2600(16)00048-5. |
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ABBREVIATIONS
IGRAs: interferon-gamma release assays
LAM: lipoarabinomannan
MTB: Mycobacterium tuberculosis
NPA: nasopharyngeal aspirates
WHO: World Health Organization