O:13a,13b, a new pathogenic serotype of Yersinia enterocolitica.

Forty strains of a new Yersinia enterocolitica serotype isolated in the United States from nonhuman primates and humans were characterized as serotype O:13a,13b. Most of the human strains were isolated from a large multistate outbreak of milkborne enteritis. A common antigenic factor between this new serotype and four previously described Y. enterocolitica (O:7,13; O:18; O:44; and O:44,45) led to recharacterization of the latter as serotypes O:7,13a,13b; O:18,13b; O:44,13a; and O:44,13a,45.