CHARACTERIZATION AND SEROEPIDEMIOLOGY OF A TYPE-5 ASTROVIRUS ASSOCIATED WITH AN OUTBREAK OF GASTROENTERITIS IN MARIN-COUNTY, CALIFORNIA

The Marin County strain of type 5 astrovirus was associated with two separate outbreaks of nonbacterial gastroenteritis in California in 1978. A safety-tested, bacterium-free filtrate prepared from a stool specimen of an individual who was ill during the original outbreak was given orally to 19 adult volunteers. One volunteer developed a gastrointestinal illness, and nine had serologic responses. Several diarrheal stool specimens from the ill volunteer contained a large number of 27-nm particles. By using immune electron microscopy with acute- and convalescent-phase sera from the original outbreak, these 27-nm particles were shown to be identical to the viral inoculum. The Marin County virus, purified from the stool of the ill volunteer, was shown by immunoprecipitation and polyacrylamide gel electrophoresis to contain a single structural protein with a molecular weight of 30,000. The buoyant density of the virion was 1.39 g/cm3 in cesium chloride. By electron microscopy, approximately 5% of the particles had the characteristic stellate configuration of astrovirus, and serologic studies by immunofluorescence technique confirmed previous classification of the Marin County virus as a type 5 astrovirus. Radioimmunoassay and biotin-avidin immunoassay were used to detect antibody to the Marin County virus in paired acute- and convalescent-phase sera from 32 outbreaks of nonbacterial gastroenteritis, but none of these outbreaks could be attributed to this virus. Prevalence of antibody to this strain of astrovirus was approximately 13% in children 6 months to 3 years of age and increased to 41% in older children and young adults.