ABSTRACT
Objective To investigate the prevalence of influenza virus infections in infants and young children during the pandemic period of 2009 influenza A(H1N1)in Beijing.Methods Throat swabs were collected from children visited the affiliated Children's Hospital to Capital Institute of Pediatrics for influenza-like illness from June 1,2009 to February 28,2010.The specific gene segments of 2009 pandemic influenza H1N1 and seasonal influenza viruses were amplified from samples by real-time RT-PCR recommended by WHO and National Influenza Reference Center of China.Results Out of 4363 clinical samples tested by real-time RT-PCR,the total positive rate of influenza A viruses was 29.3%,including 623(14.3%)identified as 2009 pandemic influenza A(H1N1)and 657(15.1%)influenza A viruses without subtype identity.Among those pandemic influenza H1N1 positive,23 were severe cases with 5 deaths.The ages for 618 pandemic influenza H1N1 infected children with completed information were from 14 days to 16 years.The ratio of male to female wag 1.3:1.Among them,25.2% were patients in age group of 1 to 3 years old and distribution of children in age groups of 3 to 6 years old and 6 to 12 years old were similar(about 30.0%).During the survey period,it appeared only one prevalence wave of pandemic influenza H1N1.The positive rate of pandemic H1N1 increased in September and the peak(36.5%of positive rate)was in November and then declined to 2.7%in February 2010.The data from routine influenza virus surveillance from 20-30 clinical samples collected each week indicated an alternative prevalence of seasonal H3N2,pandemic H1N1 and influenza B during this study period.Respiratory syncytial virus(RSV)became predominant in children after the circulating of pandemic H1N1.Conclusion There was an epidemic of pandemic influenza H1N1 in children in Beijing from June 2009 to February 2010,especially in those of preschool and school aged children.Seasonal influenza viruses and pandemic influenza H1N1 were contributed alternatively.