Fluorescent antibody responses of cases and contacts of hand, foot, and mouth disease.

Paired sera from clinical cases, familial contacts, and school contacts of hand, foot, and mouth disease were tested by indirect immunofluorescence against a strain of coxsackie A16 virus which had been adapted to human fibroblast tissue-cultured cells. All of the 22 clinical cases developed immunoglobulin (Ig) G antibodies, and 11 responded with IgM and 10 with IgA antibodies. Seventeen of 21 familial contacts of cases showed subclinical infection as determined by development of IgG antibodies. Only seven and nine, respectively, of these had demonstrable IgM and IgA antibodies. Thirteen of 16 school classmates of three clinical cases were shown to have experienced subclinical infection by the development of IgG antibodies. Only five had antibodies in the IgM fraction, and three had antibodies in the IgA fraction. A comparison of IgG titers with those obtained by neutralization tests provides further evidence that the indirect fluorescent antibody technique represents a rapid diagnostic procedure for this disease.