Epidemiology of influenza from 2017 to 2022 in a national children's regional medical center

BackgroundTo examine the changes in influenza types (A/B), including influenza A subtypes (A(H1N1) / A(H3N2)) and influenza B lineages (B/Victoria and B/Yamagata) in children in Hangzhou City, China.MethodsThis retrospective study was conducted in a national children's regional medical center, using data from children screened for influenza between January 2017 and December 2022.Results6775 patients (3 months to 14 years, 54.16% boys) were identified to have influenza-like symptoms. Among all patients, 905 (13.36%) patients were positive for the influenza virus. The number of patients positive for influenza was 222 (21.31%), 129 (12.40%), 270 (25.71%), 59 (5.15%), 37 (3.03%), and 188 (14.72%) from 2017 to 2022, respectively. The prevalence of influenza was higher in the more than 6 years old (n = 332, 23.23%) and 3-6 years old (n = 397, 13.18%) than in the under 3 years old (n = 176, 7.54%) groups, indicating that the influenza infection might increase with age. A/H3N2 infection was highest in the under 3 years old and 3-6 years old age groups while B/Victoria infection was highest in the more than 6 years old age group. The positive rates of influenza A (7.41% vs. 7.22%, P = 0.767) and B (5.47% vs. 5.94%, P = 0.407) among boys and girls did not have much difference The seasonal characteristics showed that, among patients with influenza-like symptoms, winter and spring were the dominant flu season in Hangzhou. The most common virus subtypes were B/Victoria in the spring and A/H3N2 in other seasons. The influenza positive rates among different seasons were different, in winter it was higher compared with the other seasons except for 2021 and 2022, results also revealed that influenza A/H3N2 had a relatively high prevalence in summer.ConclusionsThe influenza viruses infection rate in 3 months to 14 years participants ranged from 3.03 to 25.7%, and the positive rate increased with age. No significant difference was observed in different sexes and subtypes of influenza. However, the relatively high prevalence of influenza A/H3N2 and high prevalence of all four subtypes indicate more attention to influenza infection should be paid in summer and winter.