Surveillance of influenza-like illness in Longgang district of Shenzhen city, Guangdong province, 2005-2007

Objective　To analyze the surveillance results of influenza in Longgang district of Shenzhen city, Guangdong province and predict the epidemic trend of influenza and the virus variation. Methods　The epidemiological, etiological and serological surveillance data of influenza in Longgang district from 2005 to 2007 were analyzed to explore the epidemic pattern. Results　A total of 26 644 influenza-like illness cases were reported from February, 2005 to December, 2007, accounting for 5.30% (26 644/503 182) of the total outpatient cases, and most cases occurred among children aged 15 years (83.17%). Influenza occurred all the year round, and the cases during May-September accounted for 62.70% (16 707/26 644). A total of 20 strains of influenza virus were isolated with the positive rate of 1.96%, including 16 strains of A virus and 4 strains of B virus. During this 3-year period, 37 outbreaks occurred with 605 cases accumulatively. Most outbreaks occurred during March-June and in primary and middle schools. Etiological test indicated that A virus was predominant in 2005 and 2007 (73.33%) and B virus was predominant in 2006 (68.18%). Conclusion　The influenza activity in Longgang district from 2005 to 2007 was relatively stable without large-scale outbreaks and no significant virus variation was observed.