Use of solid-phase immune electron microscopy for classification of Norwalk-like viruses into six antigenic groups from 10 outbreaks of gastroenteritis in the United States.

Norwalk-like viruses observed in fecal specimens from 10 outbreaks of gastroenteritis investigated in the United States between 1987 and 1992 were analyzed by solid-phase immune electron microscopy. Outbreak virus strains were classified into six antigenic groups: the four types (UK1 to UK4) previously defined in the United Kingdom, Norwalk virus, and the Oklahoma agent that was newly defined in this study. The diversity of antigenic types demonstrated in these outbreaks was greater than previously recognized and will serve as a basis for characterization of these strains at the molecular level.