To find out whether the appearance and pathogenicity of infections caused by echovirus 22 (EV22)--which has considerably different molecular characteristics from those of typical enteroviruses--exhibit extraordinary features, novel diagnostic approaches were applied. Staining of inoculated cell cultures with specific antibodies was followed by immunoperoxidase detection. Of fecal specimens from 140 children under 6 years of age, four were positive by the immunoperoxidase method. The nucleotide identity between these samples and additional EV22 isolates from Finland and the United States varied from 78% to 93% when studied by specific polymerase chain reaction, followed by sequence analysis of the amplicons. One-hundred ten single serum specimens collected from individuals in different age groups to find out the prevalence of EV22 antibodies were subjected to neutralization tests. Out of 21 neonates, 20 (95%) had EV22 antibodies, probably of maternal origin. Of 10 children aged 2-12 months, only two had neutralizing antibodies to EV22. The antibody levels increased rapidly by age, and among 30 adults tested, 29 (97%) were seropositive. A clear difference was observed with the occurrence of echovirus 30 (EV30) antibodies, which were less prevalent and appeared later in life. A review of previously published studies concerning the epidemiology of EV22 infections showed that gastroenteritis and respiratory infections are the most common symptoms observed in EV22 infections.