Xpert MTB/RIF Ultra performance on bronchial specimens in diagnosing pulmonary tuberculosis in Vancouver, Canada
Bibliographic record
Abstract
Introduction. In cases where sputum is non-diagnostic or unavailable, bronchoscopy can yield high-value respiratory samples for tuberculosis (TB) diagnosis. Whilst Mycobacterium tuberculosis (MTB) complex culture remains the gold standard, molecular assays such as Xpert MTB/RIF Ultra (Xpert Ultra) are increasingly being used for rapid diagnosis. Gap Statement. Xpert Ultra is increasingly used for TB diagnosis and has been extensively evaluated on sputum specimens, but assessment of performance on bronchoscopy samples is more limited. Aim. To retrospectively evaluate the performance of Xpert Ultra on bronchoscopy specimens in comparison to culture in a low-incidence, high-resource setting. Methodology. Patients with a clinical suspicion of TB, who had non-diagnostic sputum or limited sputum production and underwent bronchoscopy between March 2019 and October 2023, were included in the study. Bronchoscopy specimens comprised bronchoalveolar lavages, bronchial washings and endobronchial ultrasound lymph node tissue biopsies. All included specimens underwent acid-fast bacilli (AFB) smear, mycobacterial culture and Xpert Ultra. Positive MTB culture was considered the reference standard for TB diagnosis. Results. One hundred thirty-five bronchoscopy samples from 126 patients were included. Cultures were positive for MTB in 47 out of 126 (37.3%) of included patients. Overall, positive percent agreement (PPA) and negative percent agreement (NPA) of Xpert Ultra to MTB culture were 93.6% and 98.7%, respectively. In 19 AFB smear-positive cases, Xpert Ultra had 100% PPA and NPA, whilst in 28 smear-negative cases, PPA and NPA were 89.3% and 98.6%, respectively. On average, positive culture results were available after 15.2 days of incubation (range, 5–42 days) versus 24 h for Xpert Ultra. Xpert Ultra PCR cycle threshold values correlated strongly with AFB-smear grade and time-to-culture positivity. Conclusion. Xpert Ultra performed on specimens collected via bronchoscopy demonstrated excellent agreement with culture, even in smear-negative cases. Our results support the use of the Ultra on bronchoscopy specimens for accurate and rapid TB diagnosis in a low-incidence setting.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.004 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.002 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".