Familial outbreak of Yersinia enterocolitica serotype O9 biotype 2

In Japan, infection with Yersinia enterocolitica of the pathogenic serobiogroup serotype O9 biotype 2 (O9/2) has rarely occurred, and familial outbreaks of Y. enterocolitica are also infrequently reported. We found a familial outbreak of Y. enterocolitica O9/2. Y. enterocolitica O9/2 was detected from stools collected from three persons in the same family. Two patients (an 11-month-old girl and her 68-year-old grandmother) contemporaneously suffered from enterocolitis, and the third person, a carrier (a 5-year-old girl), manifested no symptoms. This bacteria was not detected from other family members or from their pet hamster. All the bacteria obtained from the three people were genetically identified by pulsed-field gel electrophoresis (PFGE). The infection route was likely to have been via food, because Y. enterocolitica was not found from the pet hamster. This is the first report of a familial outbreak of Y. enterocolitica O9/2 genetically identified by PFGE in Japan.