OBJECTIVETo identify the pathogen and characteristics on a case of hand-foot-mouth disease (HFMD) caused by coxsackie-virus A6 (CA6) associated with vaccine-derived poliovirus (VDPV) co-infection.

METHODSField epidemiological study at the epidemic area was conducted and 16 stool samples including from the patient and close contacts were collected for isolation and identification of the enterovirus (EV). 21 stool samples from patients diagnosed as HFMD were collected in the same hospital at the same month to detect CA16,EV71, CA6 and PV by real-time RT-PCR or RT-PCR. The VP1 gene of the CA6 was amplified by RT-PCR and PCR products were sequenced and analyzed.

RESULTSThe patient showed only HFMD symptoms, but no symptoms related to acute flaccid paralysis (AFP). No EVs were isolated from 16 samples collected from the patient and close contacts. And no AFP cases were found by an active search. A total of 21 samples from patients diagnosed as HFMD were collected in the same hospital at the same month and 4 were found to be EV71, 2 were CA16 and 15 (include the patient)were CA6. Only this patient was found to have had VDPV II infection. The CA6 VP1 gene was amplified from the HFMD patient and 9 other cases from the same hospital at the same month. Nucleotide sequences of the VP1 gene among the 9 strains shared 98.9%-100.0% in homology and 96.0%-100.0% in the deduced amino acid sequences. Phylogenetic analysis of the VP1 sequences categorized the 9 strains into the same branch. There were 6 nucleotides changes including U2909A between the VP1 region of the VDPV strain of the case and Sabin II. Results from phylogenetic analysis on the VP1 sequences indicated that the VDPV strain of the case was different from other VDPVs strains isolated in the world.

CONCLUSIONThis case was a HFMD which caused by CA6 co-infection with VDPV II and the VDPV was newly discovered. HFMD symptoms of the case were caused by CA6. The reason why this case did not have AFP symptoms was probably due the protective effect of IPV vaccine. No AFP cases were found by the active search for AFP cases conducted in the area, which indicated that VDPV did not cause virus circulation in this area.