Circulating pattern of influenza B viruses in Xicheng district in Beijing,2009-2011

Objective To understand the circulating pattern of influenza B viruses in Xicheng district in Beijing and provide evidence for developing prevention and control measures. Methods From October 2009 to September 2010, throat swabs were collected from influenza like illness (ILI) patients in two hospitals in Xicheng district for influenza virus isolation by using MDCK cells. Hemagglutination inhibition test was conducted to identify the types or subtypes of isolated strains. Results Among 3393 throat swabs, 106 were positive in influenza B viruses detection, the positive rate was 3.12%. The highest positive rate was 19.65% in January 2010. There were two epidemics in Xicheng district, respectively, during January-February 2010 and during March-April 2011. The mean age of the positive cases was 2520 years and the positive rate in people aged 60 years was highest. Conclusion The major circulating strain of influenza B virus belonged to Victoria lineage. Influenza B viruses mainly affected adolescent and old people in Xicheng district. It is necessary to strengthen the disease surveillance and take timely prevention and control measures when the epidemic occur to protect the public's health.