Co-circulation of coxsackieviruses A6 and A10 in hand, foot and mouth disease outbreak in Finland

Abstract Background A nationwide outbreak of hand, foot and mouth disease (HFMD) occurred in Finland in autumn 2008. The outbreak was untypical since a considerable number of clinically diagnosed patients were adults. Furthermore, many of the patients suffered from onychomadesis several weeks after the acute phase of HFMD. Objectives Detection, identification and phylogenetic analysis of human enteroviruses (HEV) that caused the outbreak. Study design A total of 420 clinical specimens were obtained from 317 HFMD cases all over the country. The presence of HEV in the specimens was analysed by virus isolation and/or direct real-time RT-PCR; selected HEV strains were further typed by molecular methods. The genetic similarities of HEV strains were assessed by phylogenetic analyses on partial VP1 sequences. Results HEV were detected in 212 HFMD cases, including both children and adults, throughout Finland. Two HEV types, coxsackieviruses A6 (CV-A6) and A10 (CV-A10), were identified as the causative agents of the outbreak. One genetic variant of CV-A6 predominated, but, additionally, three other genetically distinct CV-A6 strains were found. All CV-A10 strains segregated into one genetic cluster distinct from previously reported CV-A10 sequences. Conclusions The Finnish 2008 HFMD outbreak was caused by two infrequently detected, co-circulating, coxsackie A viruses. Our data suggest endemic circulation of both CV-A types in Northern Europe and that the outbreak was due to the emergence of new genetic variants of these viruses.