Abstract
Epidemiology and clinical course of influenza in hospitalized children: a single-center retrospective study during one epidemic season
Department of Pediatric Infectious Diseases and Pediatric Hepatology, St. John Paul II Hospital, Cracow, Poland
Pediatric Center for Infectious Diseases and Neuroinfections, Jagiellonian University Medical College, Cracow, Poland
Faculty of Medicine and Health Sciences, Andrzej Frycz Modrzewski Cracow University, Cracow, Poland
Cracow Center for Research and Innovative Technologies, St. John Paul II Hospital, Cracow, Poland
Institute of Heart Diseases, Wroclaw Medical University, Wroclaw, Poland
Department of Cardiovascular Surgery and Transplantology, St. John Paul II Hospital, Cracow, Poland
Department of Pediatrics, Jagiellonian University Medical College, Cracow, Poland
Pediatr Pol 2026; 101 (2): 113-121
Introduction
Influenza is exceedingly common in children worldwide and places a substantial burden on healthcare systems. We aimed to evaluate the epidemiology, clinical course, and laboratory characteristics of seasonal influenza in hospitalized children during a single infection season.
Material and methods
We analyzed data from children with laboratory-confirmed influenza hospitalized at a single center from September 2022 to August 2023. The clinical course was compared across three age groups (< 2, 2–7, and > 7 years) and by influenza type (A or B).
Results
Among 1,344 hospitalized children, 150 (11.2%) had laboratory-confirmed influenza. Ninety children (61.2%) were infected with influenza A and 57 (38.8%) with influenza B. Three patients with dual A/B infection were excluded, leaving 147 children for the final analysis. Their mean age was 3.7 ±3.3 years (range 1 month –14 years), and 81 (55.1%) were male. Most patients were < 7 years old (85.0%). Children with influenza A were younger (3.1 ±3.0 vs. 4.8 ±3.5 years, p = 0.014), had higher C-reactive protein and white blood cell counts (p < 0.05). Bronchiolitis occurred more often in children with influenza A (14.4% vs. 1.7%, p = 0.011). In contrast, children with influenza B more frequently experienced headaches (19.3% vs. 6.7%, p = 0.020), myositis (24.4% vs. 5.5%, p < 0.001) and laboratory abnormalities, including leukopenia (45.6% vs. 22.2%, p = 0.005), thrombocytopenia (22.8% vs. 2.2%, p < 0.001), and increased aspartate aminotransferase > 3× the upper reference limit (22.8% vs. 4.4%, p < 0.001). The most common complications were pneumonia (17.7%) and otitis media (16.3%), regardless of the type of influenza. Most children were unvaccinated (98.6%). The peak incidence occurred in December, with influenza A predominating from October to January and influenza B prevailing during the spring months (p < 0.001).
Conclusions
Influenza A and B had a broadly similar clinical course; however, the virus type and patient age shaped complication patterns, underscoring the importance of age-adapted clinical assessment and improved preventive strategies in children.
Keywords
children, pediatrics, seasonal influenza, influenza complications
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