The virus isolation analysis of the H5N1 subtype human avain influenza cases in mainland China from 2005 to 2009

Objective To analyse the correlation between the virus isolation and the specimen collection of the H5N1 human hish pathogenic avain influenza cases in Mainland China.Methods The specimens were collected in Mainland China from 2005.10 to 2009.3 and the H5N1 viruses were isolated by passage in embryonated chicken eggs.Results Most specimens were obtained within 14 days after disease onset.For the specimens collected within 7 days,the isolation rate was relatively high and the difference of the positive rate between different years was lower than those specimens collected after 7 days.Most of the samples in our study were collected from the upper or lower respiratory tract with few from blood,feces,et al.The isolation rate of lower respiratory specimens was higher and the difference of the positive rate between different years was relatively lower than those from upper respiratory specimens.Conclusion We suggest that the samples should be collected from lower respiratory tract during the acute phase to get the higher isolation rate. Key words: Influenza A virus; Avain; Virus cultivation; Selection bias