In our study, it was found that the adenoviruses infected in hospitalized children with ARTI were mainly type 3 and type 7. Higher percentage of shortness of breath, multilobar infiltration, and pleural effusion were observed in clinical symptoms of type 7. A study noted that the main type of AdV infections among inpatients and outpatients in south China were type 7 . A study by Yali Duan  et al. noted that a cross-sectional study of nine hospitals in different provinces of China pointed out that the predominant types in the northern local epidemic were types 3 and 7, and the predominant types in the southern region were types 2 and 3. In addition, a shift in the predominant AdV endemic type from type 3 to type 7 was monitored in Guangdong, and this change in type may have caused the AdV outbreak in the southern region in 2018 . The findings of these studies are generally consistent with our results, implying that there are no significant differences in the AdV types leading to ARTI across Chinese provinces.
ARTI is a common disease in children, which can occur throughout the year and has a high morbidity and mortality rate, seriously affecting the lives of people worldwide, and AdV infection is one of the important pathogens causing ARTI in children . AdV is commonly found in nature and AdV infections have been reported worldwide. Since 1953, when Rowe first isolated AdV, and 1958, when research on AdV infections began in China, previous reports indicated that 100 serotypes have been identified, divided into two genera, mammalian AdV and avian AdV, while human AdV is divided into 7 subgroups A-G, with more than 80 different serotypes, which can exist as regional, epidemic and sporadic infections with worldwide, or outbreaks epidemics . Different types of human AdV have different characteristics such as histophilia, pathogenicity, and endemic areas, and are mainly transmitted through droplets, contact, and fecal-oral, etc. Patients with AdV infection and those with occult infection are the main sources of infection, which can cause pneumonia, pharyngeal-conjugate fever, tonsillitis, cystitis, encephalitis, and enteritis, etc. Most patients have mild or insignificant symptoms, but the infection can also spread to the whole body and severe pneumonia, and even death; in addition, AdV infection can leave different degrees of sequelae, and most patients have a poor prognosis, which has a serious impact on the quality of life of the children . Therefore, it is necessary to analyze the typology and clinical characteristics of AdV infection in children with ARTI in order to provide a basis for clinical prevention and treatment.
As AdV recombination leads to the continuous emergence of novel types, the International AdV Organization believes that the acquisition of the three gene sequences, five-neighborhood, six-neighborhood and fibronectin, is necessary to determine the AdV type . The results of the present study showed consistent results of typing of 231 cases with 3 genes, where 49.78% (115/231) of AdV type 3, 41.56% (96/231) of type 7 and 8.66% (20/231) of other types were identified, which is consistent with the results of the above study. The results of Lin  et al. pointed out that type 7 infections have lower white blood cell counts than type 3 infected children and higher calcitonin pro and C-reactive protein levels were high. The results of the present study showed that type 7 wheezing or shortness of breath, multilobar infiltrates, pleural effusion proportion and calcitoninogen were significantly higher than type 3 and other types, and leukocyte count was lower than type 3 and other types (P < 0.05), suggesting that the inflammatory response is higher in children with ARTI with AdV-positive gene type 7 who have more symptoms of wheezing or shortness of breath and a reduced leukocyte count and higher levels of calcitoninogen. The results of the present study differ from the above-mentioned studies in that the results of the present study did not find any difference in C-reactive protein levels between type 3 and type 7 infections. In addition, the comparison of critical AdV pneumonia, admission to pediatric intensive care unit (PICU), invasive mechanical ventilation and death among type 3, type 7 and other types in this study (P > 0.05), but type 7 critical AdV pneumonia, admission to PICU, invasive mechanical ventilation and death were slightly higher than type 3 and other types, which may be analyzed because type 7 AdV infection is more likely to progress to severe disease. The study by Xie  et al. noted that type 7 AdV infections are more likely to progress to severe pneumonia, with higher oxygen requirements and longer hospital stays. Similarly, Fu  et al. showed through in vivo, in vitro and clinical correlation analysis that type 7 AdV has a greater replication capacity compared to type 3 AdV and can promote and exacerbate cytokine responses, resulting in a more severe respiratory inflammatory response.
There are shortcomings in this study. The results of this study are retrospective and only represent the typology and clinical symptoms of AdV infection in children admitted to our hospital with ARTI. In addition, significant differences in the distribution of AdV infection subtypes between children in the north and south of China have been previously found, and subsequent multicenter studies need to take into account sampling in the north and south. Moreover, the recently discovered association of severe acute hepatitis with AdV and SARS-CoV-2 should be included in subsequent studies if possible.