[Molecular epidemiology of human enterovirus 71 strains in Qingdao region, Shandong province, 2007 - 2009].

OBJECTIVE: To study the molecular epidemiology of human enterovirus 71 (EV71) isolated from patients with hand-foot-mouth disease (HFMD) in Qingdao region between 2007 and 2009. METHODS: Throat swabs of HFMD were detected for total enterovirus (EV), EV71 and CA16 by fluorescence reverse transcription-polymerase chain reaction (RT-PCR). The VP1 region was amplified from positive EV71 specimens and 51 nucleotide sequences of VP1 gene were successfully sequenced. EV71 genotypes were characterized by phylogenetic analysis. RESULTS: 51 Qingdao EV71 strains identified between 2007 and 2009 belonged to C4a cluster of subgenotype C4 and 5.3% nucleotide divergence and 1.7% amino acid divergence were found among them. The strains in 2008 and 2009 were respectively divided into several lineages on phylogenetic trees but there was a main lineage (namely prominent strain) every year. The Qingdao prominent strains identified in 2008 had high identities with the Linyi prominent strains in 2007. The Qingdao prominent strains in 2009 and the secondary prominent strains in 2008 had high identities with the Fuyang prominent strains in 2008. Two Qingdao strains in 2007 had high identities with the Linyi popular strains in 2007. CONCLUSION: Data showed that several EV71 transmission chains were co-circulating in Qingdao between 2008 and 2009. The main transmission chain in 2008 became the minor one but the minor transmission chain in 2008 was transferred into the main transmission chain in 2009.