Etiologic structure of severe acute respiratory viral infections in children of different ages in the post-COVID period

Background: The etiology of acute respiratory infections includes more than 300 simultaneously circulating viruses. Identification of a specific pathogen is only possible using molecular genetic methods. Acute respiratory infections most commonly affect young children (under 6 years of age), school-age children, and adults over 65 years. In some cases, infection symptoms require hospitalization. Aim: To investigate the etiology of severe acute respiratory infections in children of different ages during the epidemic seasons of 2022–2024. Methods: A total of 646 nasopharyngeal swabs from patients hospitalized in pediatric hospitals in Yekaterinburg were examined using reverse transcription polymerase chain reaction. Specimens were collected according to approved criteria and tested for viral pathogens, including influenza A and B viruses (INFA, INFB) and other respiratory viruses included in the standard diagnostic panel. Results: Over two epidemic seasons, 646 children were examined: 267 in 2022–2023 and 379 in 2023–2024. During this time, more than 60.0% of severe acute respiratory infections were confirmed viral. In 2022–2023, influenza accounted for 52.2% of cases. In this period, influenza A(H1N1)pdm09 virus and influenza B virus were circulating. Among non-influenza viruses, respiratory syncytial virus (HRsV), rhinovirus (HRV), and bocavirus (HBoV) were identified. In the following season, most cases of severe acute respiratory infections were caused by respiratory viruses, including HRsV, HRV, and adenoviruses (HAdV). Influenza A(H3N2) virus predominated among influenza cases. Analysis of coinfections with several respiratory viruses in one patient showed that in 2023–2024 the frequency of mixed infections more than doubled. In most cases, respiratory viruses were responsible for coinfections. Conclusion: It is crucial to study the etiologic agents of respiratory infections in children that require hospitalization. This is especially relevant in the post-pandemic period of SARS-CoV-2, when circulation of other respiratory viruses, particularly influenza viruses, was suppressed.