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

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.

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.

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%.

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.