Etiology and Epidemiology of Acute Lower Respiratory Infections Among Hospitalized Pediatric Patients in Northeastern China: A Retrospective Study from 2023 to 2025

Purpose: To analyze the etiological and epidemiological characteristics of acute lower respiratory infection (ALRI) in hospitalized children in Northeast China (Shenyang, Liaoning Province) following the lifting of non-pharmaceutical interventions (NPIs). Patients and Methods: Clinical data and test results for 12 respiratory pathogens from 26,721 hospitalized children with ALRI admitted to two hospitals in Shenyang between January 2023 and December 2025 were retrospectively analyzed. Pathogen detection was performed using polymerase chain reaction (PCR) or serological methods. To control for diagnostic heterogeneity, analyses were stratified by PCR and serology as follows: chi-square test for age, gender, and seasonal distributions; multivariate logistic regression for independent factors associated with pathogen positivity; and Spearman’s rank correlation test for associations between meteorological factors and monthly positivity rates. Results: PCR testing showed that rhinovirus (RV) had the highest positivity rate (13.80%), followed by influenza A virus (IAV) and respiratory syncytial virus (RSV). RSV was most common in infants aged < 1 year, while RV and IAV were more common in children aged 3-< 6 years. The positivity rate of RV was higher in males than in females ( P < 0.001). IAV and RSV peaked in winter and spring, whereas RV peaked in summer. Serological testing showed that Mycoplasma pneumoniae (MP) had the highest positivity rate (37.64%), followed by RSV and adenovirus (ADV). The detection peaks of MP and ADV were concentrated in children aged 6– 14 years. The positivity rates of Epstein-Barr virus (EBV), MP, and Chlamydia pneumoniae (Cpn) were lower in males than in females (all P < 0.05). MP peaked in autumn and winter, while IAV peaked in winter. The age and seasonal distribution patterns of RSV were consistent with those from PCR testing. Age, season, and gender were independent influencing factors for pathogen infection. Meteorological factors were significantly correlated with monthly positivity rates of specific pathogens ( P < 0.05). Conclusion: Following the lifting of NPIs, the pathogen spectrum of childhood ALRI in Shenyang presented distinct seasonal, age, and gender differences. Age, season, and gender were independent influencing factors for pathogen infection. Although methodological differences exist between PCR and serological testing, comparisons within the same detection method are generally reliable.