OBJECTIVETo characterize the prevalence and occurrence of subgroups of human respiratory syncytial virus (RSV) in infants and young children with acute respiratory infections (ARI) in Beijing area.

METHODSRSVs were identified from nasopharyngeal aspirates and throat swabs collected from infants and children with ARI who visited the Children's Hospital Affiliated to Capital Institute of Pediatrics during the period of November 2000 to March 2006, by virus isolation in Hep-2 cells and antigen detection by indirect immunofluorescence assay (IFA). RT-PCR was used to differentiate subgroups A and B of RSV from part of the positive specimens.

RESULTSOut of 10 048 specimens including 7176 nasopharyngeal aspirates from inpatients and 2872 throat swabs from outpatients, 2286 (22.8%) were RSV positive. The positive rate for RSV identification were 30.0% (2153/7176) in specimens from the hospitalized patients, which was higher than that from outpatients (4.6%, 133/2872). The youngest of the RSV positive patients was 1 day after birth and the oldest was 15 years of age, with 73.0% younger than 1 year. Among those RSV positives, only 1.6% were older than 5 years. The ratio of male to female who were RSV positive was 2.4:1 (1598:674). The clinical diagnosis for 91.2% (1991) of those RSV positive patients was severe lower respiratory infections including bronchiolitis and pneumonia, whereas in only 8.8% (192) the diagnosis was upper respiratory infections. The data revealed that RSV started to be detected in October each year during the survey period and November to next April was the RSV season. The detection rate declined in May and almost no RSV could be found in summer. Positive rates for RSV detection were 42.3%, 41.0% and 40.5% in the seasons of 2001 - 2002, 2003 - 2004, 2005 - 2006, which were higher than those in seasons of 2000 - 2001 (14.0%), 2002 - 2003 (18.2%), 2004 - 2005 (20.4%). Subtyping of A and B during the surveillance period showed that 73.7% (691/938) were subgroup A and 26.3% (247/938) were subgroup B. Subgroup B was predominant in the 2000 - 2001 and 2004 - 2005 seasons, whereas subgroup A predominated in the 2001 - 2002, 2002 - 2003 and 2003 - 2004 seasons. Almost equal proportions of subgroup A and B appeared in 2005 - 2006 seasons.

CONCLUSIONThe data indicate that RSV is an important etiological agent for lower respiratory infections in infants and young children in winter and spring during the survey period. The pattern of RSV circulation varied alternately with higher rate every other year. The predominant subgroup changed between A and B, and co-circulated in equal proportion in some years.