ORIGINAL PAPER
Epidemiology and clinical course of influenza in hospitalized children: a single-center retrospective study during one epidemic season
1
Department of Pediatric Infectious Diseases and Pediatric Hepatology, St. John Paul II Hospital, Cracow, Poland
2
Pediatric Center for Infectious Diseases and Neuroinfections, Jagiellonian University Medical College, Cracow, Poland
3
Faculty of Medicine and Health Sciences, Andrzej Frycz Modrzewski Cracow University, Cracow, Poland
4
Cracow Center for Research and Innovative Technologies, St. John Paul II Hospital, Cracow, Poland
5
Institute of Heart Diseases, Wroclaw Medical University, Wroclaw, Poland
6
Department of Cardiovascular Surgery and Transplantology, St. John Paul II Hospital, Cracow, Poland
7
Department of Pediatrics, Jagiellonian University Medical College, Cracow, Poland
Submission date: 2025-12-04
Final revision date: 2026-01-27
Acceptance date: 2026-02-28
Publication date: 2026-06-30
Pediatr Pol 2026;62(2):113-121
KEYWORDS
TOPICS
ABSTRACT
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.
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.
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