Two-Year Pathogen Dynamics, Coinfection Features, and Core Risk Factors Associated With Severe Pediatric Acute Respiratory Tract Infections in Hangzhou, China.

BACKGROUND: Acute respiratory tract infections (ARTI) remain a major public health burden in children globally. Nevertheless, regional data regarding postpandemic pathogen shifts, coinfection profiles, and risk factors associated with severe pediatric ARTI in Hangzhou, China, remain scarce. METHODS: A retrospective observational study was conducted on 6701 hospitalized pediatric patients (0-18 years) with ARTI in Hangzhou, China, from July 2023 to June 2025. Eleven respiratory pathogens were detected using fluorescence PCR-capillary electrophoresis. Univariate and multivariable logistic regression analyses, alongside three machine learning models, were employed to identify risk factors. Age-stratified and coinfection analyses were also performed. RESULTS: Rhinovirus (RV), Mycoplasma pneumoniae (Mp), and respiratory syncytial virus (RSV) were the most prevalent pathogens. The coinfection network was centered on RV, Mp, and adenovirus, with RV-Mp being the most common dual infection. Mixed infections were associated with severe illness (4.3% vs. 3.5% in single infections vs. 1.6% in pathogen-negative cases). Mp, bocavirus (Boca), and RV infections, along with reduced percentages of lymphocytes, monocytes, and eosinophils, were independent risk factors associated with severe illness, whereas older age was a protective factor. Logistic regression demonstrated the best predictive performance. CONCLUSIONS: This study elucidates the dynamics of pediatric ARTI pathogens and coinfection characteristics 2 years postpandemic in Hangzhou, China. It identifies key risk factors associated with severe pediatric ARTI, providing essential evidence to inform age-specific clinical prevention, targeted interventions, and public health strategies for pediatric ARTI in the region.