Specific IgM antibody in serum of patients with herpes zoster infections

Specific IgM varicella-zoster antibody was detected in "convalescent" sera from 20 out of 40 patients (50%) with herpes zoster infections. Since these were not primary infections with varicella-zoster virus, it seems that detection of IgM antibody specific for a particular virus may not differentiate a primary infection from secondary infections with that virus.