Hepatitis A: report of a common-source outbreak with recovery of a possible etiologic agent. II. Laboratory studies.

During investigation of a food-borne outbreak of hepatitis A among university students in a southwestern metropolitan community, immune electron microscopic examination of a concentrated stool suspension pooled from seven acutely ill individuals revealed viruslike particles 17-nm in diameter. These particles were initially coated by antibody contained in the convalescent-phase serum of one of the ill students as well ad by antibody in convalescent plasma of a prison volunteer originally infected with the MS-1 strain of hepatitis A virus. Rises in titer of antibody to this particle were demonstrated by immune electron microscopy in acute and convalescent sera from student patients as well as in pre-inoculation and convalescent sera from the prison volunteer. Two chimpanzees inoculated intravenously with the concentrated preparation of pooled human stools developed viral hepatitis. During acute illness their feces contained particles morphologically identical to those in the inoculum. These findings represent the first reported recovery of the presumed etiologic agent of hepatitis A from a naturally occurring community outbreak of disease in the United States.