Jpn.J.Infect.Dis., 52, 1999

Laboratory and Epidemiology Communications

Detection of a Multi-Prefectural E. coli O157:H7 Outbreak Caused by Contaminated Ikura-Sushi Ingestion

Jun Terajima, Hidemasa Izumiya, Sunao Iyoda, Kazumichi Tamura and Haruo Watanabe*

Department of Bacteriology, National Institute of Infectious Diseases, 1-23-1, Toyama, Shinjuku-ku, Tokyo

Communicated by Hiroshi Yoshikura

(Accepted May 10, 1999)

After multiple outbreaks all over Japan in 1996, enterohemorrhagic E. coli (EHEC) O157:H7 was classified as one of the designated diseases whose outbreaks are obligatorily reported to the local health authority. Since then, the prefectural public health laboratories, in collaboration with the National Institute of Infectious Diseases (NIID), have conducted analyses of EHEC isolates by pulsed-field gel electrophoresis (PFGE). PFGE based on analysis of the whole genome by restriction endonuclease XbaI digestion has proven useful for investigation of EHEC outbreaks and for sporadic cases (1). A substantial amount of data on mass and sporadic outbreaks has now accumulated. Diffuse outbreaks of EHEC O157:H7 that occurred in March 1997 in the southern part of the Kanto and Tokai areas (the middle part of Honshu) were caused by contaminated radish sprouts, and all cases of the O157:H7 exhibited the same PFGE pattern (2).

From May to June in 1998, diffuse outbreaks of O157:H7 were reported from Toyama Prefecture and Tokyo. Foods that had been ingested by the patients were investigated to determine the source. It was found that the patients had all ingested Ikura-Sushi (cakes of rice with salmon roe). The salmon roe implicated in the outbreaks had been prepared by a single manufacturer in Hokkaido.

O157:H7 strains isolated in various parts of Japan from patients who had ingested Ikura-Sushi and those isolated directly from the salmon roe processed in Kanagawa and other prefectures were sent to NIID for PFGE analysis. Among human isolates, 47 out of 52 showed an identical PFGE pattern which was coded as pattern A (Fig. 1). The other 5 isolates, lacking two of the bands in PFGE, were coded as pattern B. Both patterns were obtained in the direct isolates from the salmon roe processed in Kanagawa Prefecture and Hokkaido. All the isolates, from the patients and the salmon roe, had the same phage type 14. The data confirmed that the diffuse outbreaks had been caused by the contaminated salmon roe prepared by one manufacturer (3).

Analyses using PFGE and phage typing combined with epidemiological data eventually revealed that the outbreak involved 49 clinically manifest patients and 13 asymptomatic carriers dispersed in 7 prefectures and municipalities, including Toyama, Tokyo, Chiba, Kanagawa, Osaka, Yamanashi, and Ibaragi.

We thank the prefectural and municipal public health institutes in Japan for providing the EHEC O157:H7 isolates.


  1. Izumiya, H., Terajima, J., Wada, A., Inagaki, Y., Itoh, K., Tamura, K. and Watanabe, H. (1997): Molecular typing of enterohemorrhagic Escherichia coli O157:H7 Isolates in Japan by using pulsed-field gel electrophoresis. J. Clin. Microbiol., 35, 1675-1680.
  2. National Institute of Infectious Diseases (1997): Verocytotoxin-producing Escherichia coli (enterohemorrhagic E.coli) infections, Japan, 1996-June 1997. Infect. Agent Surveillance Rep., 18, 153-154.
  3. Asai, Y., Murase, T., Osawa, R., Okitsu, T., Suzuki, R., Sata, S., Yamai, S., Terajima, J., Izumiya, H., Tamura, K. and Watanabe, H. (1999): Isolation of Shiga toxin-producing Escherichia coli O157:H7 from processed salmon roe associated with the outbreaks in Japan, 1998, and a molecular typing of the isolates by pulsed-field gel electrophoresis. J. Jpn. Assoc. Infect. Dis., 73, 20-24 (in Japanese).

*Corresponding author: Haruo Watanabe, FAX: +81-3-5285-1171 , E-mail:

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