Surveillance of influenza in Longgang district of Shenzhen,Guangdong province,2007 - 2009

Objective To analyze the results of influenza surveillance in Longgang district of Shenzhen, and provide evidence for the development of influenza prevention and control strategies. Methods The data of the epidemiological surveillance and etiological surveillance of influenza like illness (ILI) cases, the data of avian influenza serum antibody level surveillance among the people with occupational exposure and the data of influenza serum antibody level surveillance among risk population from 2007 to 2009 were analyzed. Results A total of 78 650 ILI cases were under surveillance, accounting for 7.29% of the total outpatients. The cases were mainly distributed in 0-and 5-age groups, accounting for 79.92%, and the disease occurred all the years round with high incidence during April-August, accounting for 55.89%. A total of 316 influenza virus strains were isolated during this period, including 25 strains of seasonal influenza A viruses, 60 strains of influenza B viruses and 183 strains of 2009 pandemic influenza A (H1N1) virus. A total of 126 influenza outbreak occurred during this period, resulting in 1381 cases. The outbreaks mainly occurred during June-July and September-November, accounting for 78.57%. Primary and middle schools were the setting where influenza outbreaks were prone to occurred, the cases there accounting for 80.95%. Influenza A viruses were predominant (60.00%) in 2007, influenza B viruses were predominant (57.58%) in 2008 and 2009 pandemic Influenza A (H1N1) virus was predominant (56.96%) from August in 2009. Conclusion The incidence of seasonal influenza was relatively stable in Longgang district from 2007 to 2008, without large-scale outbreak. 2009 pandemic influenza A (H1N1) influenza activity was observed from August to November in 2009.