[Water-borne outbreak of Yersinia enterocolitica O8 due to a small scale water system].

: A water-borne outbreak of Yersinia enterocolitica O:8 associated with a small-scale water system occurred during July-August 2011 in Toyama Prefecture, Japan. Escherichia coli was not detected in tap water from the small-scale water system. However, the maximum concentration of viable bacteria in the tap water was 700CFU/mL, which exceeds the legal standard for purity of tap water (100CFU/mL). Furthermore, Y. enterocolitica O8 was isolated from the tap water with the use of immunomagnetic beads prepared with anti-Y. enterocolitica O8 antibodies. Pulsed-field gel electrophoresis analysis identified 3 isolates from tap water and 5 isolates from 4 patient stool specimens as belonging to the outbreak strain. An epidemiological investigation revealed improper management of the residual chlorine concentration in the tap water. This is the first report of an outbreak of Y. enterocolitica due to tap water from a small-scale water system in Japan.