Etiology, Clinical Manifestations, and Age Characteristics of Mixed Viral Respiratory Infections Within 2024-2025

Introduction: This study aims to investigate mixed viral respiratory infections, examining their causes, age patterns, and the involvement of co-pathogens in the lower respiratory tract infections (LRTIs). Materials and methods: A total of 2825 nasopharyngeal samples were collected from April 2024 to March 2025. Multiplex real-time PCR assays were used to test for 13 respiratory viruses, while capillary electrophoresis was used to determine viral load. Results: This study identified 180 (6.4%) cases of coinfections with respiratory viruses, predominantly involving bocaviruses (BoVs) (51%), rhinoviruses (RVs) (38.8%), and influenza A viruses (34.4%). Children under 5 had the highest mixed infection rate (13.5%), especially involving respiratory-syncytial virus (RSV), rhinoviruses (RVs), adenoviruses (AdV), and bocaviruses (BoVs). The co-infection rate in patients with bronchiolitis was significantly higher than that in patients with infections restricted to the nose, sinuses, and pharynx (p=0.0006). RSV was most commonly associated with bronchiolitis cases (54%). Children under 2 years with mixed infections faced a greater risk of developing lower (58%) versus upper respiratory tract infections (URTIs) (39%) (p = 0.0276). Additionally, in co-infected patients with lower respiratory tract complications (LRTCs), SARS-CoV-2 had higher viral loads compared to those of other co-pathogens. Conclusion: This study found a relatively low rate of mixed respiratory viral infections, with BoVs RVs, and influenza A viruses being the main causative agents. Children under two years of age are particularly vulnerable and are at higher risk of severe complications such as bronchiolitis. Understanding the interactions of these viruses is essential for developing effective treatments and prevention strategies for this at-risk group.