Surveillance for influenza B virus infections in infants and young children in Beijing, China / 中华儿科杂志

ABSTRACT

<p><b>OBJECTIVE</b>To characterize the prevalence of influenza B virus infection in infants and young children in Beijing.</p><p><b>METHODS</b>MDCK cell culture, indirect fluorescence assay (IFA) and hemagglutination inhibition (HI) assay were used to isolate and identify type B influenza viruses from clinical samples collected from outpatients and inpatients who visited the Affiliated Children's Hospital because of acute respiratory infections from Nov. 2000 to Jun. 2006.</p><p><b>RESULTS</b>Out of 10,770 clinical samples collected during this surveillance period, 384 (3.57%, 384/10,770) were positive for influenza B viruses. Circulation of influenza B viruses was revealed in the later epidemic season of influenza viruses each year. The detection rate for influenza B virus was higher than 10% each year during the survey, except in the period from 2003--2004 which was 2.91%. The highest detecting rate was 23.69% of the specimens collected in Mar. 2006. During the period of this study, most of the influenza B virus were identified from children who visited the outpatient department of the Affiliated Children's Hospital. Among those outpatients who were positive for influenza B, 77.6% (264/340) were older than 3 years of age, whereas the inpatients positive for influenza B, 66.0% (29/44) were under 3 years of age. Coinfection of influenza B virus with other respiratory viruses was not common, only one of the influenza B virus positive specimen was found also positive for influenza A3. There was no significant difference in positive rate between influenza virus B and A3. A significantly higher positive rate of influenza B virus than that of influenza A3 virus was seen from Sep. 2005 to May 2006 (23.9% vs 1.1%). B/Yamagata/16/168 lineage viruses were dominant during 2000--2002, and B/Victoria/2/87 lineage viruses became dominant during 2002--2003. After 2003, co-circulation of Victoria and Yamagata lineages of influenza B viruses was identified with predominance of Yamagata lineage viruses, while Victoria lineage viruses predominated during the 2005--2006 epidemic season.</p><p><b>CONCLUSION</b>Influenza B viruses were identified from February to May in every influenza season during this surveillance period of 2000--2006. Most of the positive specimens were those collected from outpatient department. Victoria and Yamagata lineages of influenza B viruses co-circulated in Beijing, China in recent years.</p>