Epidemiological dynamics of respiratory tract infections in a major northern coastal city (Dalian), China, following the COVID-19 pandemic

To elucidate the epidemiological characteristics, including population distribution, temporal patterns, and co-infection rates, of major respiratory pathogens circulating in China to provide evidence for precision prevention and clinical management of respiratory tract infections (RTIs). We retrospectively analyzed nucleic acid test (NAT) data from 15,426 RTI patients at a university hospital in Dalian, China, between January 2023 and December 2024. Six key pathogens were assayed: Mycoplasma pneumoniae (MP), influenza A/B (Flu A/B), respiratory syncytial virus (RSV), adenovirus (ADV), and human rhinovirus (HRV). Positivity rates and seasonal patterns were statistically compared across different genders and age cohorts. The overall pathogen positivity rate was 27.9%. MP (10.5%) and Flu A (7.3%) were the predominant causative agents. The overall positivity rate was significantly higher in females than males (29.3% vs. 26.7%; p = 0.022), and detection rates for MP, Flu A, and HRV also showed gender-specific differences (p < 0.05). The highest positivity rate was observed in the children’s group (1–12 years, 80.0%), with MP being the most dominant pathogen (51.3%). Conversely, Flu A predominated in adults and the elderly. Seasonal analysis revealed a “high in winter and low in summer” pattern overall. Flu A and RSV peaked during winter, while MP exhibited an atypical biannual peak in autumn. Co-infections were detected in 2.2% of patients. Among co-infected patients (n = 334), the most frequently observed patterns being Flu A/MP (15%) and HRV/MP (14%). The prevalence of major respiratory pathogens in China demonstrates significant variations across age, gender, and seasonal dimensions. MP and Flu A are the primary etiological agents. These findings advocate for strengthened seasonal surveillance and targeted strategies, specifically focusing on MP in pediatric populations and Flu A in adults and the elderly, with intensive monitoring of Flu A and RSV during autumn and winter.