Background Human bocavirus(HBoV)is a parvovirus recently found to possibly cause respiratory tract disease in children and adults.This studV investigated HBoV infection and its clinical characte rist:ics in children younger than five years of age suffering from acute Iower respiratory tract infection in Beijing Children's Hospital.Methods Nasopharyngeal aspirates were collected from children suffering from acute Iower respiratory tract infection during the winters of 2004 to 2006 (from November through the following February).HBoV was detected by polymerase chain reaction amplification and virus isolation and the amplification products were sequenced for identification.Results HBoV jnfection was detected in 16 of 333 study subjects.Coinfections with respiratory syncytial virus were detected in 3 of 16 HBoV positive patients with acute lower respiratory tract infection.The median age for HBoV positive children was 8 months(mean age,17 months;range,3 to 57 months).Among the HBoV positive children,14 were younger than 3 years old.9 were younger than 1 year old and 7 were younger than 6 months.These 16 positive HBoV children exhibited coughing and abnormal chest radiography findings and more than 60%of these children had wheezing and fever.Ten children were clinically diagnosed with pneumonia,2 bronchiolitis,2 acute bronchitis and 2 asthma.One child died.Conclusions HBoV was detected in about 5%of children with acute Iower respiratory infection seen in Beijing Children's Hospital.Fudher investigations regarding clinical and epidemiologic charactedstics of HBoV infection are needed.