Association between real-time polymerase chain reaction cycle threshold value and clinical presentation in children with Bordetella pertussis.

Background: The cycle threshold (Ct) value is inversely proportional to the number of copies of the target region in a sample, suggesting that a low Ct value indicates a high pathogen load. The relationship between Ct value and clinical presentation in children with pertussis is not well-defined.

Methods: We investigated the relationships between the Ct value of nasopharyngeal samples positive for Bordetella pertussis deoxyribonucleic acid via real-time polymerase chain reaction (PCR), collected from children on admission and their adult family members between May 2022 and March 2024 at Hangzhou Children's Hospital, China. The study focused on the correlation between Ct value and clinical presentation in children with pertussis.

Results: The Ct value was positively correlated with age (r = 0.362, P = 0.001). The mean Ct value for children with pertussis was 28.0 (range: 22.0-32.0), which was lower than the 32.0 (range: 30.0-34.0) observed in adults. Ct value was inversely correlated with length of stay, an indicator of disease severity (r = -0.356, P = 0.001). Logistic regression analyses revealed that both Ct value (OR: 0.891, 95% CI: 0.799-0.993, P = 0.036) and white blood cell count (OR: 1.127, 95% CI: 1.005-1.263, P = 0.040) were independently associated with severity of pertussis.

Conclusions: Real-time PCR Ct values at initial diagnosis for pertussis may potentially predict severe disease outcomes in children.