What is the Significance of a High Cycle Threshold Positive IS481 PCR for Bordetella pertussis?
Bibliographic record
Abstract
To the Editors: We read with great interest the article by Waters et al regarding an outbreak of atypical pertussis diagnosed by polymerase chain reaction (PCR).1 It is well established that PCR targeting the IS481 gene, of which there are 50 to 200 copies per bacterial cell, is a highly sensitive method for detecting Bordetella pertussis.2 Indeed, with this assay, a positive result with a cycle threshold (CT) value >35 likely represents the detection of less than 1 organism per sample.2,3 Consequently, it remains unclear how to interpret a late-cycle positive PCR result. Does it represent detection of true pertussis disease (possibly modified by vaccination, partial natural immunity or antimicrobial therapy)? Or, does it represent transient colonization where B. pertussis was an innocent bystander with regards to the clinical syndrome that prompted diagnostic testing? Given that Walters et al used a CT of ≤40 to define a case, and given that their mean CT value was 38.4, further analysis is necessary to understand the clinical relevance of their results and to shed light on the dilemma of interpreting CT values >35. To do so, it would be invaluable to look for the existence of an association between higher CT values and the presence of coinfection with other respiratory pathogens (as tested by PCR on the study's pertussis-positive nasopharyngeal samples). Furthermore, a receiver operating characteristic curve would help elucidate how CT cut-off values affect the diagnostic assay's sensitivity and specificity when compared with a reference standard such as the clinical case definition of pertussis. Jesse Papenburg, MD, FRCPC Infectious Diseases Division, Department of Pediatrics and Department of Microbiology Montreal Children's Hospital, McGill University Health Centre Montreal, Canada Infectious Disease Research Centre Centre Hospitalier Université Laval Quebec City, Canada Patricia Fontela, MD, MSc Department of Epidemiology and Biostatistics McGill University Montreal, Canada
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.011 | 0.088 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.003 | 0.001 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.003 |
| Scholarly communication | 0.005 | 0.005 |
| Open science | 0.005 | 0.001 |
| Research integrity | 0.016 | 0.020 |
| Insufficient payload (model declined to judge) | 0.003 | 0.003 |
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 source (direct Gemma or distilled Codex), 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".