Nosocomial infections are common in pediatric patients and can be fatal in infants and immunocompromised patients.In September 2018,a high positive rate of human adenovirus HAdV was occurred among hospitalized children in the Children\'s Hospital Affiliated to the Capital Institute of Paediatrics in Beijing.To investigate whether this outbreak of HAdV was related to nosocomial infections or the result of community infections,we collected respiratory specimens from patients with acute respiratory infections in a respiratory ward during June to December 2018,and screened for respiratory viruses.Among 1,840 cases included,95(5.2％,95/1840)were positive for HAdV and 81 were genotyped based on phylogenetic analysis,including seven as HAdV-1(8.6％),30 HAdV-3(37.0％),two HAdV-6(2.5％),and 42 HAdV-7(51.9％).More HAdV-positive samples were collected in August(4.7％,12/255),September(15.0％,41/274)and October(6.9％,17/247),with a peak in September 2018.By combining the results of HAdV phylogenetic analysis with clinical data of patients,there were 77 cases(4.2％,77/1840;81.1％,77/95)excluded from nosocomial infections,eight cases repre-senting possible infections transmitted by visitors or attending parents,three cases without sequences that might have been due to infection transmitted by roommates positive for HAdV,one case of a roommate without an HAdV sequence,and six cases that shared highly homologous sequences with those of their roommates,for which nosocomial infections might be considered.In conclusion,genotyping of HAdVs based on phylogenetic analysis combined with clinical information provides a powerful method to distinguish nosocomial infections from community acquired infection,especially when tracing the origins of nosocomial infections.