OBJECTIVETo elucidate the etiology of acute respiratory tract infection (ARI) in hospitalized children in Suzhou from 2005 to 2011.

METHODSA total of 10 243 hospitalized children with ARI in Children's Hospital Affiliated to Soochow University from September 2005 to October 2011 were enrolled in the study. The clinical information was collected; and the nasopharyngeal aspiration fluid and serum samples were sent for multi-pathogen detection. Respiratory syncytial virus (RSV), influenza virus type A and B (IV-A, IV-B), parainfluenza virus type 1-3 (PIV-1-PIV-3) and adenovirus (ADV) were detected by direct immunofluorescence assay. Human bocavirus (HBoV), mycoplasma pneumoniae (MP) and chlamydia pneumoniae (CP) were detected by fluorescent quantitative PCR while human metapneumovirus (hMPV) was detected by reverse transcription PCR (RT-PCR). Sputum culture was applied to detect bacterial infection and quantitative ELISA was adopted to detect the specific antibodies of MP and CP. The results of the above detections were analyzed, and thereby to explore the prevalent pathogens among different aging children and the seasonal distribution and characteristics of the disease.

RESULTSAt least one type of pathogen was detected in 5871 out of 10 243 hospitalized children and the overall positive rate was 57.32%; including 3326 virus samples with positive rate at 32.47% (3326/10 243), 2870 bacteria samples with positive rate at 28.02% (2870/10 243) and 2759 atypical pathogen samples,with positive rate at 26.94% (2759/10 243). MP was the most common pathogen,whose detected rate was 25.74% (2637/10 243). The median age of children with RSV (6 months) or PIV-3(8 months) infection was younger than the median age of all hospitalized children (12 months) (χ(2) = 380.992, 34.826, P < 0.05). While the median age of children with ADV (42 months), HBoV (14 months) or IV-A (24 months) infection was older than it of all hospitalized children (χ(2) = 83.583, 13.169, 18.012, P < 0.05). The median age of children with MP (30 months),streptococcus pneumoniae (17 months) or haemophilus parainfluenzae (21 months) infection was older than it of all hospitalized children (χ(2) = 728.299, 60.463, 8.803, P < 0.05). The detected rate of RSV in the groups of children aging less than 6 months, 7-12 months, 2-3 years, 4-5 years and over 6 years was separately 25.59% (840/3283), 17.05% (333/1953), 11.85% (310/2615), 6.68% (90/1347), and 2.87% (30/1045); which decreased while the age grew (χ(2) = 178.46, P < 0.01). Conversely, the positive rate of MP increased with the age growing (χ(2) = 379.21, P < 0.01). The rate in the above groups was 8.25% (271/3283), 19.46% (380/1953), 33.00% (863/2615), 41.43% (558/1347), 54.07% (565/1045), respectively. RSV and IV-A were prevalent in winter, whose detected rates were 35.73% (941/2634) and 4.44% (117/2634) respectively.hMPV infection was common in spring, with the detected rate at 10.55% (278/2634); while HBoV infection was common in summer and autumn, with the positive rate at 9.99% (149/1491) and 9.71% (98/1009). MP and CP were frequently detected in summer, up to 31.27% (819/2619) and 10.07% (43/427) respectively. RSV was the most common pathogen in bronchiolitis (33.27% (866/2603)) and MP was the most common pathogen in bronchopneumonia (26.05% (1152/4422)) and lober pneumonia (52.25% (267/511)).

CONCLUSIONMP and RSV were the most common pathogens in respiratory tract infection in hospitalized children. The novel virus included hMPV and HBoV, which also played an important role in ARI. Different pathogens were prevalent in different ages; with respective seasonal distribution and characteristics.