OBJECTIVETo monitor the seasonal distribution of influenza types and subtypes in Wuxi area during 2005-2008, and to investigate the variation in hemagglutinin (HA) genes of A/H3N2 strains in 2008.

METHODSNose-throat swab specimens were collected in Wuxi area from flu-like patients from outpatient departments of hospitals as well as from clustering flu-like outbreak patients from workspace, followed by MDCK cell inoculation. Types and subtypes of positive influenza isolates were identified using standard antiserum. We then sequenced the HA genes for H3 subtype influenza viruses isolated from 2008 specimens to investigate the variation in HA genes.

RESULTSDuring 2005 and September 2008, 435 strains of influenza viruses were isolated from flu-like patients in Wuxi Area, among which 164 isolates are of A/H1N1 subtype, 80 isolates are of A/H3N2 subtype, and 191 isolates are of B type. These types/subtypes have significant seasonal distributions. Sequences of HA genes for H3 subtype show that the 9 strains isolated in Wuxi area are similar to those of strains isolated in Shanghai within the same period. Many of the sequences belong to the same branch of the phylogenetic tree, and are similar to sequences of vaccine strains in WHO 2008-2009 repositories.

CONCLUSIONA/H1N1, A/H3N2 and B still attribute to most of the sporadic and local outbreaks of influenza infection in Wuxi area in recent years. HA genes of A/H3N2 strains isolated in Wuxi area are similar to those of strains isolated in Shanghai in the same period, and also similar to those of vaccine strains recommended by WHO for 2008-2009.