Rapid diagnosis of echovirus 33 infection by neutralizing specific IgM antibody

In 1982, we isolated 20 strains of echovirus type 33 (EV33) from 18 patients. We studied the humoral response to EV33 of 2,437 subjects from whom at least one serum was available during the same year. In 388 subjects with the neutralizing antibody level at 64 or more, we assayed the EV33 IgM antibodies by seroneutralization test after fractionation of sera by ion exchange chromatography. One hundred ninety-five subjects (8.0%) had a high titre (greater than or equal to 32) of EV33 IgM antibodies, which was considered as evidence of recent infection. The EV33-positive IgM fractions were assayed against five other enteroviruses. Sixty percent of the IgM fractions did not cross-react with any of the five serotypes, 8.7% cross-reacted with at least one serotype but with predominant EV33 IgM response, and 31.3% had an equivalent or greater amount of non-EV33 IgM antibodies; the type specificity of the assay was directly related to the age of the subjects. These findings suggest that determination of neutralizing specific IgM antibody is a sensitive and rapid test for the diagnosis of enterovirus infections, especially in young people.