[Immune and inflammatory characteristics and risk factors of severe influenza in pediatric intensive care unit]

Objective: To investigate the immunological and inflammatory features of severe influenza and risk factors for critical influenza in children admitted to the Pediatric Intensive Care Unit (PICU). Methods: A retrospective cohort study was conducted. Clinical data was collected from 334 children with severe influenza admitted to the PICU of Shanghai Children's Hospital between January 2023 and December 2024. Data included baseline characteristics, organ function parameters, immunological indicators, and lymphocyte subsets measured within 24 h of PICU admission. Patients were stratified into severe and critical groups according to the influenza diagnostic criteria. Group comparisons were performed using independent-sample t test, Mann-Whitney U test, χ² test, or Fisher's exact test for general characteristics, laboratory findings, and immune parameters. Multivariate Logistic regression analysis was employed to identify independent risk factors for critical influenza. Results: Among the 334 children (195 males (58.4%) and 139 females (41.6%)), the age was 5.9 (3.6,9.0) years. The severe group comprised 184 patients (55.0%), and the critical group comprised 150 patients (45.0%), with an overall mortality of 9 cases (2.7%). The main clinical phenotypes included respiratory failure (83 cases), influenza-associated encephalopathy and(or) encephalitis (71 cases), coagulation dysfunction (30 cases), shock (15 cases), and acute kidney injury (10 cases). Compared to the severe group, the critical group exhibited significantly lower counts and percentages of CD8⁺ and CD4⁺ T cells, natural killer cell counts, fibrinogen,complement C1q, and complement C4 (all P<0.05). Conversely, the critical group had significantly higher levels of interleukin (IL)-6, IL-10, IL-8, neutrophil-to-lymphocyte ratio (NLR), procalcitonin, percentage of CD19⁺ B cells, prothrombin time, and D-dimer (all P<0.001). Multivariate logistic regression analysis identified IL-6, NLR, CD19⁺ B cell percentage, and D-dimer as independent risk factors for critical influenza (OR=1.23, 1.17, 1.11, 1.69, 95%CI 1.02-1.54, 1.05-1.30, 1.04-1.18, 1.20-2.39, respectively; all P<0.05). Conclusions: Hyperinflammation response and elevated D-dimer are independent risk factors for the development of critical influenza in children. Early assessment of immune and inflammatory markers provides valuable reference for the identification and management of critical influenza.