Seroprevalence of varicella-zoster virus immunoglobulin G antibodies in Swiss adolescents and risk factor analysis for seronegativity

BACKGROUND: Little is known about the seroprevalence of anti-varicella-zoster virus (VZV) serum antibodies in adolescents in Switzerland as in most other European countries. METHODS: Serum specimens from 13- to 15-year-old students from eight urban and rural areas in Switzerland, obtained as part of an allergy risk assessment study project (SCARPOL), were available for analysis of IgG antibodies against VZV by enzyme-linked immunosorbent assay (ELISA) and confirmation by fluorescent antibody staining of membrane antigen in a subcohort. Serum specimens and comprehensive sociodemographic data had been collected during two study periods between 1992 and 1995. RESULTS: Data and serum specimens were available from 1709 and 1788 subjects, respectively. Seroprevalence of anti-VZV antibodies as measured by ELISA was 95.5% (95% confidence interval, 94.5 to 96.4). When serum specimens that were indeterminate by ELISA were tested by FAMA, seroprevalence was 96.5% (95% confidence interval, 95.7 to 97.4). After logistic regression analysis, the number of siblings was the only factor that significantly influenced the presence of VZV antibodies (90.1% in those with no siblings, <96% with 1 or more siblings), whereas residence (urban vs. rural), parental education, nationality and gender did not. CONCLUSIONS: Seroprevalence of anti-VZV serum antibodies is comparatively high among Swiss adolescents. Individuals who grow up without siblings have a significant risk of evading natural VZV infection in childhood, and they therefore form a potential target group for varicella immunization in Switzerland.