Epidemic characteristics of hand, foot, and mouth disease in Shanghai from 2009 to 2010: Enterovirus 71 subgenotype C4 as the primary causative agent and a high incidence of mixed infections with coxsackievirus A16.

BACKGROUND: Enterovirus 71 (EV71) has been the main causative agent of hand, foot, and mouth disease (HFMD) outbreaks in recent years. A significant increase in the number of HFMD cases in China over the last 3 y has made the public prevention and therapy of this disease a critical issue.

METHODS: A total of 3208 HFMD patients in Shanghai during the period 2009 to 2010 were analyzed; 437 clinical specimens were collected for the determination of causative pathogens. Eight of the isolated EV71 strains were sequenced and phylogenetically analyzed.

RESULTS: The widespread outbreak of HFMD in Shanghai was caused predominantly by EV71 (86.5%), and in part by coxsackievirus A16 (CA16) (6.9%). The high incidence of mixed infections with EV71 and CA16 (17.6% of the total CA16-infected cases) has never before been observed in China. Most HFMD patients (76.9%) were aged 1-4 y. Boys showed a higher HFMD prevalence rate (65.3%) than girls (34.7%). Phylogenetic analysis on the basis of the VP1 gene and the complete genome sequences revealed that the EV71 strains that circulated in Shanghai belonged to the C4 subgenotype.

CONCLUSIONS: EV71 subgenotype C4 was the major causative agent of the HFMD outbreak in Shanghai. A high incidence of mixed infections with EV71 and CA16 was also observed.