Background: Influenza surveillance aims to determine onset, duration and intensity of the seasonal Influence-like Illness (ILI); data collection begins in the week 42 of a year and ends in the week 17 of the following year. In this observational study, we report the experience of a tertiary care children hospital in Rome about Influenza viruses circulation during the calendar year 2022 (January-December) in comparison with the previous five years (2017-2021), with a special focus on the weeks 18-41, usually not under surveillance.
Methods: This retrospective study involved 36782 respiratory samples referred to 21354 patients (pts), median age 2.63 years, admitted with respiratory symptoms at Bambino Gesù Children's Hospital in the years 2017-2022. Respiratory viruses were detected by molecular Allplex™ Respiratory Panel Assays (Seegene, Korea).
Results: Regarding the pre pandemic years, 2017-2019, distribution of Flu positive patients focused in the first weeks of the year (weeks 1-17). During the pandemic period, Flu was not detected. In 2022, 239 Flu viruses were identified: 37 FluA (weeks 1-17), 29 FluA (weeks 18-41) and 168 FluA and 5 FluB (weeks 42-52). For the year 2022, during the non-epidemic period, the number of Flu viruses detected corresponded to 12.1% of total Flu detected, respect to 0-1.7% for the previous five years (p < 0.001).
Conclusions: When compared with pre SARS-CoV-2 pandemic years, our data show a significant increase in Influenza cases during weeks 18-41/2022 and reveal an unexpected summer circulation of these viruses: just weeks 26-30 showed to be influenza virus free. A national year-round Flu surveillance could be useful to understand if changing in influenza epidemiology is transitional or likely to persist in the following years.
Keywords: Influenza; Influenza-like Illness; Out-of-season circulation; Pediatric; Seasonality; Year-round surveillance.
© 2023. Società Italiana di Pediatria.