Etiology and Clinical Manifestations of Acute Respiratory Infections in Pediatric Patients: A Retrospective Study in Moscow, Russia

Background/Objectives: Acute respiratory viral infections (ARVIs) are the leading cause of pediatric morbidity and exhibit considerable clinical heterogeneity. The analysis of clinical and etiological associations, as well as the identification of factors linked to severe ARVI cases, is essential for effective epidemiological surveillance. Methods: A retrospective, single-center observational study was conducted including 1362 non-COVID-19 pediatric cases of acute respiratory infections (ARIs), registered between 2021 and 2024. Viral pathogens were detected using real-time PCR for broad-spectrum screening of respiratory viruses. Results: Viral etiology was established in approximately 50% of cases. The most frequently detected pathogen was Human rhinovirus (HRV) (35.6%), followed by Respiratory syncytial virus (RSV) and Human adenovirus (HAdV). Despite its predominance, HRV did not demonstrate nosological specificity. The strongest associations with lower respiratory tract infections were identified for RSV (OR = 3.2) and Human bocavirus (HBoV; OR = 2.4), predominantly within the pneumonia category. RSV was also associated with bronchitis/bronchiolitis (OR = 1.8). Significant associations with upper respiratory tract infections were established for Influenza viruses (OR = 10.4) and HAdV, including nasopharyngitis (OR = 3.88) and acute tonsillitis (OR = 3.9). HAdV additionally demonstrated an association with otitis media (OR = 5.1). Severe disease was registered in 52.3% of all clinical observations and occurred most frequently among young children, particularly in cases associated with respiratory syncytial virus (RSV >80%), as well as with human bocavirus (HBoV) and Human metapneumovirus (HMPV) (~55–59%). Co-infections were not associated with increased disease severity compared with monoinfections (OR = 1.1). Conclusions: The obtained results highlight the contribution of specific etiological agents to severe respiratory infections in children. These findings support the prioritization of such pathogens in clinical diagnostics, including the design of diagnostic algorithms and the selection of patient management strategies in pediatric populations.