Introduction: Hyperleukocytosis among infants with Bordetella pertussis infection (i. e. malignant pertussis MP) can be treated with exchange transfusion (ET) /leukapheresis (LA), yet there is no consensus on a white blood cell (WBC) count threshold to initiate ET/LA. We aimed to assess the association and discriminatory capacity of admission WBC count for inpatient mortality among critically ill infants with MP and characterize the use of ET/LA. Methods: In a multicenter retrospective cohort study using the Virtual Pediatric Systems (VPS) database including infants ≤6 months of age from 91 hospitals undergoing invasive ventilation for MP from 2009-2025, we assessed inpatient mortality (i. e. primary outcome) by admission WBC count (i. e. explanatory variable). Area under the receiver operator characteristic curve (AUROC) was used to assess the discriminatory capacity of WBC count for mortality yielding a threshold value via Youden’s Index. We employed a multivariate logistic model to identify associations between mortality, admission WBC count, and ET/LA. Results: Of 273 ventilated infants with MP, the median admission WBC count was 25. 4x10³ cells/µL (interquartile range, IQR: 13. 7-50. 9) and greater for 34 (12. 5%) infants who died compared to survivors (61. 7x10³ cells/µL IQR: 48. 7-71. 4 vs 21. 7x10³ cells/µL IQR: 13-39. 3, P< 0. 001). Admission WBC count strongly discriminated mortality (AUROC: 0. 80, 95% confidence interval CI: 0. 72-0. 88; Threshold: 44. 3x10³ cells/µL Sensitivity: 79. 4%, Specificity: 78. 7%). Eighteen (6. 6%) infants underwent ET/LA a median of 1 day IQR: 0. 25-2 after admission who when compared to those not undergoing ET/LA had a greater median admission WBC count (58. 8x10³ cells/µL IQR: 40-72. 1 vs 22. 6x103 cells/µL IQR: 13. 1-45. 9, P< 0. 001) and rate of extracorporeal support (39% vs 11. 8%, P< 0. 001), without a difference in mortality rate. In our model accounting for age and Pediatric Risk of Mortality III score, admission WBC count was associated with mortality (adjusted odds: 1. 04, 95%CI: 1. 03-1. 06, P< 0. 001) but not ET/LA. Conclusions: For infants ≤6 months of age with MP undergoing invasive ventilation, admission WBC count was associated with and discriminatory for inpatient mortality. Prospective research to evaluate ET/LA efficacy could apply the WBC threshold identified herein.
Russi et al. (Sun,) studied this question.