Also, Xpert cannot distinguish DNA derived from viable and non-viable Mtb bacilli, reducing its utility for the evaluation of treatment responses 10. Xpert and Xpert Ultra may thus detect only 20~40% of all paediatric TB cases, and their sensitivity may be even lower in children living with HIV, who may have higher rates of culture-negative TB. PCR-based Xpert MTB/RIF (Xpert) and Xpert Ultra can provide diagnostic results in a few hours but detect only a fraction of the Mtb-positive sputum (65%) and gastric samples (73%) detected by Mtb culture 9. Mtb culture, the diagnostic gold standard, is slow (2–8 weeks) and detects only 30–62% of paediatric TB (ref. However, young children frequently require invasive procedures to obtain respiratory samples that may contain few Mtb bacilli (paucibacillary TB), and often present with disseminated or extrapulmonary TB missed by respiratory sampling strategies. Most microbiologic TB assays use culture or nucleic acid amplification to detect Mycobacterium tuberculosis ( Mtb) bacilli in respiratory and extrapulmonary samples. The COVID-19 pandemic has hindered global TB-control efforts, and models from the World Health Organization (WHO) suggest that TB-notification decreases observed in TB-endemic countries in 2020 may result in hundreds of thousands of additional TB deaths 7. Most paediatric TB deaths (80%) occur in children less than 5 years old, and 96% of these deaths occur in children who are untreated owing to missed diagnoses 5, 6. Despite sustained global efforts towards the control of TB, children aged less than 15 years account for ~1 million TB cases annually and for 230,000 TB-related deaths 4. Tuberculosis (TB) is the second leading cause of death from infectious disease and a top-ten cause of death globally 1, 2, 3, with an estimated 10 million new cases and 1.2 million deaths yearly. With further development, the assay may facilitate the detection of tuberculosis at the point of care, particularly in resource-limited settings. We adapted the assay to make it portable and operable by a smartphone. It also distinguished tuberculosis from latent-tuberculosis infections in non-human primates. In a cohort study of 147 hospitalized and severely immunosuppressed children living with HIV, the assay detected 58 of the 78 (74%) cases of paediatric tuberculosis, 48 of the 66 (73%) cases that were missed by microbiological assays, and 8 out of 10 (80%) cases undiagnosed during the study. Here we report a nanoparticle-enhanced immunoassay read by dark-field microscopy that detects two Mycobacterium tuberculosis virulence factors (the glycolipid lipoarabinomannan and its carrier protein) on the surface of circulating extracellular vesicles. Sensitive and specific blood-based assays for the detection of pulmonary and extrapulmonary tuberculosis would reduce mortality associated with missed diagnoses, particularly in children. Nature Biomedical Engineering volume 6, pages 979–991 ( 2022) Cite this article Diagnosis of paediatric tuberculosis by optically detecting two virulence factors on extracellular vesicles in blood samples
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