Etiology spectrum of hand, foot and mouth disease and the genetic characteristics of three predominant enterovirus stains in Qingdao in 2013

Objective To investigate the etiology spectrum of hand, foot and mouth disease (HFMD) and to analysis the molecular characteristics of three predominant human enterovirus stains in Qingdao in 2013. Methods The total enterovirus (EV) strains and strains of EV71, CVA16 and CVA6 in throat swabs of HFMD cases were detected by using multiplex real time RT-PCR. The full-length of the viral VP1 genes of the EV strains were amplified and sequenced. The sequences were phylogenetically analyzed by using the MEGA5.0 software package. Results A total of 841 patients with mild HFMD and 107 patients with serious HFMD were recruited in this study and 64.3% of them were positive for EV. The predominant pathogens were EV71 (44.8%), CVA6 (28.2%) and CVA16 (9.5%) in 2013. CVA6 replaced CVA16 as the second most common pathogen for HFMD, accounting for 42.7% of all pathogens in children aged less than 3 years and 22.2% of all pathogens in the serious patients. The proportions of CVA6 in the etiology spectrum showed a downtrend along with the increasing age of the patients (P<0.001). Phylogenetic analysis of the complete VP1 gene sequences showed that all of the EV71 strains identified in this study belonged to the subgenotype C4 (evolutionary branch C4a) and all of the CVA16 strains belonged to the subgenotype B1 (evolutionary branches B1a and B1b). There were 6 genogroups (A to F) regarding to the VP1 gene of CVA6 and all of the CVA6 strains identified in this study belonged to genogroups A and D. Among the CVA6 strains isolated in Qingdao in 2013, 83.9% belonged to genogroup A, while the rest 16.1% belonged to genogroup D. 66.7% of the CVA6 strains isolated in 2012 belonged to genogroup A, while the rest 33.3% belonged to genogroup D. All of the CVA6 strains isolated from year 2008 to 2011 in Qingdao belonged to genogroup D. Conclusion EV71, CVA6 and CVA16 were the prevalent pathogens responsible for the development of HFMD in Qingdao in 2013. The proportions of CVA6 strains in the etiology spectrum showed a downtrend with the increasing age in children. C4a was the major subtype of EV71 strains circulating in Qingdao in 2013, while B1a and B1b were the major subtypes of CVA16 strains. The pattern of endemic circulation of CVA6 strains showed a trend of changing from genogroup D to A from year 2008 to 2013. Key words: Hand, foot and mouth disease; Enterovirus; Phylogenetic analysis; Genogroup