Surveillance of influenza in Quzhou city, Zhejiang province 2009

Objective To analyze the results of influenza surveillance in Quzhou in 2009, find out the circulating trend of influenza virus, explore the epidemic pattern and provide scientific evidence for the control and prevention of influenza. Methods The analysis was conducted on the surveillance data of influenza-like illness (ILI) in sentinel hospitals, virus isolation results and outbreak information of influenza or ILI. Results The proportion of ILI cases among outpatients in Quzhou was 3.22% in 2009; which was highest (11.19%) in internal medicine emergency departments and lowest (0.77%) in pediatrics emergency departments; Of 633 samples detected, 375 strains of influenza virus were isolated with the positive rate of 59.24%, and the positive rate was highest in age group of 60 years; The isolation rate of influenza virus was highest in November. Most cases of 2009 pandemic influenza A (H1N1) were students and were aged 10 to 30 years old. The outbreaks mainly occurred in schools, accounting for 94.44%. Conclusion Seasonal influenza viruses were predominant from June to September and 2009 pandemic influenza A (H1N1) virus was predominant from October to December.