OBJECTIVEViruses are common pathogens of acute lower respiratory tract infection (ALRTI) in children. There are few studies on consecutive monitoring of viral pathogens of ALRTI in a larger cohort during the past several years. The aim of this study was to investigate the viral pathogens of ALRTI in children of different age groups and to outline the epidemic feature of different viruses.

METHOD(1) Totally 1914 (1281 male and 709 female) children with clinical diagnosis of ALRTI during the period of March 2007 to March 2010 were recruited into this study. These patients were hospitalized patients in department of internal medicine or outpatients in emergency department in Beijing Children's Hospital. The patients were divided into four groups, including 1072 patients < 1 year old, 326 patients 1- < 3 years old, 158 patients 3- < 6 years old, 358 patients ≥ 6 years old. One nasopharyngeal aspirate specimen was collected from each patient. Reverse transcription (RT) PCR methods were applied to detect common respiratory viruses including respiratory syncytial virus (RSV), human rhinovirus (HRV), influenza virus type A, B and C (IFA, IFB, IFC), parainfluenza virus (PIV) type 1-4, adenovirus (ADV), enterovirus (EV), human coronavirus (HCOV), human metapneumovirus (HMPV) and human bocavirus (HBOV).

RESULT(1) The total positive rate of viruses was 70.3%. The positive rate was 83.0% (890/1072) in the group of < 1 year old, and 80.1% (261/326) in group of 1- < 3 years old, 60.8% (96/158) in group of 3- < 6 years old and 27.7% (99/358) in group of ≥ 6 years old, respectively. There was a significant difference in the positive rate among different age groups (χ² = 2213.5, P = 0.000). The top three viruses were RSV, HRV and PIV; and the positive rates were 50.9%, 36.2% and 12.0% respectively in group of < 1 year old. (2) The epidemic seasons of RSV and HRV were winter and spring, and PIV infection was epidemic in spring and summer. (3) The detection rates of 2 or more viruses were 38.2%, 36.4%, 30.2% and 15.2% in groups of < 1 year old, 1- < 3 years old, 3- < 6 years old and ≥ 6 years old, respectively. There was a significant difference in the mixed infection rate among different age groups (χ² = 1346.00, P = 0.000).

CONCLUSIONRSV, HRV and PIV were the most predominant pathogens in younger children with ALRTI. Different viral infections had different seasonal features. Mixed infections with two or more viruses were detected in substantial proportion of patients with ALRTI, but further studies are needed to explore the clinical significance of mixed infection with viruses in patients with ALRTI.