Objective:To investigate the clinical and epidemiological features of acute respiratory adenovirus infection in children.Methods:Clinical data of 488 children with acute respiratory tract human adenovirus (HAdV) infection admitted in Children’s Hospital of Zhejiang University School of Medicine from September 2018 to August 2019 were retrospectively analyzed. Nasopharyngeal swabs or nasopharyngeal aspirates (NPAs) were collected and tested by direct immunofluorescence assay. Kruskal Wallis H test was used for quantitative data without normal distribution, and P<0.05 was considered to be statistically significant. The qualitative data were compared by chi-square test or Fisher’s exact test. Bonfereoni chi-square segmentation was performed for comparison between groups, and P<0.007 was considered statistically significant after correction. Results:A total of 488 HAdV positive cases were detected from 7 072 patients with acute respiratory tract infection (6.9%), including 305 males (62.5%) and 183 females (37.5%). The median age of HAdV positive children was 43 months (39 days to 12 years). The detection rate in 6 m-<2 y age group(8.7%, 123/1 408)was significantly higher than those in <6 m group (3.0%, 6/197)and ≥5 y group(4.6%, 89/1 948)( χ2=7.57, 23.98, P all <0.007). The detection rate in 2-<5 y group(7.7%, 270/3 519)was significantly higher than those in <6 m group and ≥5 y group ( χ2=5.809, 19.688, P all <0.007). The peak rate was detected in the winter [12.9%(238/1 840)] which was significantly higher than those in spring (4.7%), summer (3.9%), and autumn(5.5%)( χ2=103.477, 58.986 and 49.926, P<0.007). The average length of hospital stay was (6±4)d(1-41 d). 486 cases (99.5%) were discharged from hospital after treatment, and 2 cases died. There were 111 cases (22.7%) of acute upper respiratory tract infection, 34 cases (7.0%) of bronchitis and 343 cases (70.3%) of pneumonia; and severe pneumonia was diagnosed in 86 cases (25.1%, 86/343). The common clinical manifestations were fever 93.4% (456/488), cough 94.7% (462/488), wheezing 26.2% (128/488) and shortness of breath 14.8% (72/488). 138 cases (28.3%) had extrapulmonary symptoms, 78 cases (16.0%) had underlying diseases, among which congenital heart disease was most common (16, 3.3%). The average duration of fever was(8.8±2.4)d(5-17 d)in 456 fever cases, the duration between 7-10 d in 277 cases and >10 d in 96 cases; and 439 cases had hyperpyrexia(≥39 ℃). The single infection occurred in 275 (56.4%) cases and mixed infection in 213(43.6%) cases. The proportions of fever, hyperpyrexia, fever duration >10 d, severe pneumonia, wheezing and length of hospital stay in mixed infection group were significantly higher than those in the single infection group ( χ2/ Z=11.960, 6.494, 37.209, 72.841 and -8.805, P all <0.05). The length of hospital stay, proportion of fever time>10 d, wheezing, shortness of breath, hypersomnia/poor spirits, serous effusion, extrapulmonary symptoms, mixed infection, and underlying diseases in severe pneumonia group were significantly higher than those in the mild pneumonia group ( χ2/ Z=-9.182, 23.825, 49.094, 143.627, 219.659, 81.327, 8.080, 21.546 and 10.556, P all <0.05). The proportion of severe pneumonia in 6 m to <2 y group was higher than that in 2-<5 y group and ≥5 y group( χ2=20.709, 8.603, P all <0.007). Conclusions:HAdV is an important pathogen of acute respiratory infection in children. HAdV infection occurs mainly in children aged from 6 month to 2 years and has a high detection rate in winter. Children aged 6 months to 2 years with wheezing, shortness of breath, underlying diseases, extrapulmonary symptoms and mixed infections are more likely to develop severe pneumonia.