Severe Influenza Virus Infection After COVID-19 Pandemic: Comparison of Influenza A and Influenza B

Background: Influenza is a common cause of hospital admissions worldwide, and an increase in influenza cases has been observed following the COVID-19 pandemic. Our study investigated the epidemiological and clinical characteristics of pediatric patients with influenza infection admitted to pediatric intensive care units (PICUs) in Istanbul, Turkey, following the COVID-19 pandemic. Methods: We conducted a retrospective study of pediatric patients with confirmed influenza infection who were admitted to 1 of the 11 PICUs in Istanbul, Turkey, between July 1, 2022, and June 30, 2024. Data on demographic characteristics, risk factors, clinical presentations, microbiological findings, complications and outcomes were systematically collected. Results: A total of 108 children diagnosed with laboratory-confirmed influenza required admission to the PICUs. Sixty-five (60.2%) were diagnosed with influenza A and 43 (39.8%) patients were diagnosed with influenza B. Epidemiologic and clinical characteristics were similar in both influenza types, oxygen saturation was significantly higher in the influenza A group compared to the influenza B group. Severe neurological manifestations, including seizures and encephalitis, were significantly more common in the Influenza A group. In contrast, patients with Influenza B demonstrated a higher incidence of gastrointestinal symptoms, such as nausea, vomiting and abdominal pain. Pneumonia, sepsis and/or multiorgan dysfunction and liver failure were significantly higher in influenza B. Mortality was observed solely in the Influenza B group, with six patients resulting in death, corresponding to a mortality rate of 14%. Conclusions: Influenza virus infection can cause serious multisystem complications such as acute respiratory distress syndrome and encephalitis. Influenza A can present with isolated or predominant neurological manifestations. Mortality may be more common in influenza B.