Objective: To understand the pathogen distribution characteristics of acute lower respiratory tract infections (ALRTI) in hospitalized children in the Department of Respiratory Medicine, Capital Center for Chlidren's Health, Capital Medical University from 2019 to 2023, and to analyze their epidemiological features.

Methods: A retrospective analysis was conducted, including 5 558 children aged 0-18 years who were hospitalized and diagnosed with ALRTI in the respiratory department of Capital Center for Chlidren's Health, Capital Medical University from December 8, 2019, to December 31, 2023. Nasopharyngeal swabs, sputum, and bronchoalveolar lavage fluid specimens were collected for pathogen detection.

Results: Among the 5 558 ALRTI hospitalized children, the positive detection rate of pathogens was 81.81% (4 547/5 558). In bronchoalveolar lavage fluid specimens, Mycoplasma pneumoniae had the highest detection rate (33.52%), while Streptococcus pneumoniae had the highest detection rate (24.38%) in upper respiratory tract specimens. Mycoplasma pneumoniae (54.21%, χ2=1 034.58, P<0.001) and adenovirus (5.09%, χ2=10.84, P=0.013) were most common in school-age children, human rhinovirus was more common in toddlers (26.42%, χ2=122.36, P<0.001), and respiratory syncytial virus had the highest infection rate in infants (28.61%, χ2=326.47, P<0.001). A total of 52.06% of the children had mixed infections (2 367/4 547), with the highest proportion of mixed infections in infants (62.54%). During the post- non-pharmaceutical interventions (NPIs) period, the proportions of Mycoplasma pneumoniae (69.88% vs. 58.16%), human rhinovirus (30.37% vs. 14.02%), adenovirus (51.16% vs. 6.45%), influenza A virus (36.46% vs. 16.67%), and mixed infections (33.33% vs. 19.04%) in school-age children were significantly higher than during the NPIs period. In contrast, the proportions of respiratory syncytial virus (33.19% vs. 19.42%), adenovirus (11.29% vs. 4.65%), and mixed infections (17.75% vs. 10.89%) in infants were significantly lower than during the NPIs period.

Conclusion: NPIs have changed the detection rate and epidemiology of respiratory pathogens in hospitalized children. After the end of NPIs, outbreaks of some pathogens may occur, so it is necessary to strengthen rapid pathogen detection, population surveillance, and health education.