HISTORICAL BACKGROUND HPeV are nonenveloped, positive-sense, single-stranded RNA picornoviruses that were first detected in 1956 in children with diarrhea. HPeV-1 and HPeV-2 were originally believed to belong to the genus Enterovirus (EV) and were named echoviruses 22 and 23 (1). In 1999, HPeV were assigned their genus name when genomic sequencing proved that they were not EV. At least 14 other HPeV types have been identified (Table 1) (2-34), starting with HPeV-3, which was initially reported in Japan in 2004 (21) and next reported in Canada in 2005 (35). Recombination between HPeV types may occur (31).