[Double infection with Yersinia enterocolitica 0:3 and 0:9].

An unusual case of Yersiniosis was observed in a 20-year-old woman. Except for an extraordinarily severe onset the clinical course was not remarkable. But two different strains of Yersinia were repeatedly isolated. While strain serotype 0:9 was demonstrated only transiently and gave an only weak immune reaction, serotype 0:3 persisted longer and stimulated a strong immune reaction. But both strains had similar virulence characteristics in different tests, such as plasmid demonstration, autoagglutination, growth on Ca-deficient agar, and in mice.