Comparison of the Raji cell line fluorescent antibody to membrane antigen test and the enzyme-linked immunosorbent assay for determination of immunity to varicella-zoster virus.

A prospective study was performed comparing the fluorescent antibody to membrane antigen (FAMA) test and the enzyme-linked immunosorbent assay (ELISA) for identifying susceptibility and seroconversion to varicella-zoster virus (VZV) infection. A total of 75 sera were collected from index cases and from sibling and parent contacts in 10 families. Varicella-zoster virus-infected human diploid embryonic fibroblasts and continuous lymphoblastoid cells (Raji cells) were compared as indicator cells in the FAMA test. Equivalent results were obtained with both types of cell. Results of the FAMA test and the ELISA were identical in two ways. (i) The same 11 individuals were initally defined as susceptible (seronegative), and 9 of them (82%) developed fourfold rises in antibody titers, clinical varicella, or both. (ii) Of 21 immune (seropositive) individuals, 4 developed fourfold antibody rises by FAMA tests, and 3 of these 4 responded by ELISA. Infection was asymptomatic in these individuals. The geometric mean titer by ELISA was significantly higher than by the FAMA test. The results indicated that the ELISA and the FAMA test have similar capacities to define susceptibility to varicella-zoster virus and that subclinical infection with varicella-zoster virus may be common.