Sentinel surveillance for influenza like illness in Baiyin, Gansu,2010-2013

Objective To understand the incidence pattern of influenza and circulating virus strains in Baiyin, Gansu province, and provide evidence for the prevention and control of influenza. Methods The incidence data of influenza like illness(ILI) were collected in sentinel hospitals in Baiyin from 2010 to 2013, and throat samples were taken from ILI cases to detect influenza virus nucleic acid. The statistical analysis was conducted with Excel 2003 and SPSS 19.0. Results The ILI proportion in outpatient visits was highest in 2013(1.58%), and the differences in the annual ILL proportion were statistically significant during this period(2=193.678, P=0.000), the monthly ILI proportion was highest in December and lowest in August. The highest ILI proportion was found in pediatric emergency(5.21%), and the cases were mainly distributed in children aged15 years, accounting for 65.03%. The detection rate of influenza virus was highest in 2012(26.37%), and the differences in the annual detection rate were statistically significant during this period(2=154.680, P=0.000). Among the influenza viruses detected, the proportion of influenza A(H1N1) virus A increased with year(2trend=58.773,P=0.000). The highest detection rate was in November, and the differences in the monthly detection rate was statistically significant(2=646.743, P=0.000). The detection rate of influenza virus was highest in age group 15-24 years, and the differences in the detection rate in 5 age groups were statistically significant(2=143.568, P=0.000). Conclusion Influenza season began in early winter, and the incidence of influenza peaked in winter and spring. Children and adolescents were the risk population affected by influenza. The activity of influenza A(H1N1) virus increased with year.