An outbreak of Verotoxin-producing Escherichia coli O157:H7 infection caused by lightly salted turnips in a nursing home for aged, June 2000 - Saitama
(IASR 2000; 21: 272-273)

On June 23, 2000, the Saikatsu-kita Public Health and Human Services Center, Saitama Prefecture, was notified about an outbreak of gastroenteritis among residents of a nursing home for aged in Saitama Prefecture. This report summarizes results of the outbreak investigation.

To determine risk factors for this outbreak, we conducted a case-control study among 82 long-term residents of the home. A case was defined as an acute onset of bloody stool with abdominal pain from June 14 to 30, 2000. A total of seven (8.5%) residents met our case definition with onset of illness during June 19 to 23. The median age of the six female and one male patients was 85 years (range: 78-94 years), and all had dementia. All 7 case-patients had bloody stool, abdominal pain and fever, but only 3 patients developed diarrhea. Three cases developed hemolytic uremic syndrome (HUS) or heart failure, and they died. In five patients Verotoxin 1 and 2-producing Escherichia coli O157:H7 (VTEC) was isolated from stool specimens. Stool examinations revealed one additional asymptomatic carrier among residents.

The case-control study could not identify risk factors for the VTEC infection. However, VTEC was isolated from lightly salted turnips in a frozen sample meal, which was served at the breakfast on June 15. According to information recorded in the medical charts, all 7 cases and one asymptomatic carrier had eaten breakfast containing the implicated turnips. Thus, the median incubation period was 6 days (range: 4-8 days). All isolates from the case-patients and the turnips had an identical DNA pattern by pulsed-field gel electrophoresis (PFGE). Neither descriptive nor analytic study indicated the occurrence of secondary transmission, and we concluded that the lightly salted turnips were the pathogen in this outbreak.

The lightly salted turnips were prepared in the home's kitchen by a commercial caterer in the previous evening, and were stored in a refrigerator. However, this preparation was not in compliance with Hazard Analysis and Critical Control Point (HACCP) procedures set forth by the company. All the menus with raw vegetables should have been prepared within 4 hours before serving to avoid the potential hazard of bacterial proliferation during prolonged storage. For washing vegetables, the kitchen workers used electrolyzed oxidizing water (EO water) as a disinfectant. This was the electrolyzed product (hypochlorous acid: HOCl) of deionized water containing a low concentration of sodium chloride and obtained from an electrolysis chamber in the home. Sometimes this EO water was not used immediately but was stored for several hours after production in a 20-litter tank. Experiments conducted at the Health Center laboratory revealed a rapid decrease of free-chlorine concentration of stored EO water in a short period of time. In addition, the use of EO water for washing vegetables violated the HACCP standard set forth by the catering company, which only authorizes the use of 0.01% sodium hypochlorite solution as a disinfectant.

We could not detect when and where the turnips were contaminated. None of the kitchen workers tested positive for VTEC, and VTEC was not isolated from the turnips remained in the refrigerator. Trace back on distribution route of the implicated turnips was not conducted by the Saitama Prefectural Government. No other outbreaks related with turnips have been reported during that time.

This is the first time that lightly salted turnips, commonly eaten by elderly persons, were implicated as the source of an outbreak caused by VTEC. This outbreak highlights the importance of compliance with HACCP to minimize the risk of potentially fatal foodborne outbreaks.

Reported by: Reiko Uehara, Kazue Kuramochi, Minoru Akasaka, Kenji Fukuda, Akira Amagai, and Toshiyuki Sawada, Saikatsu-kita Public Health and Human Services Center, Saitama Prefecture; Masanori Yamaguchi, Takeshi Kishimoto, and Hiroyuki Masaki, Saitama Institute of Public Health; Toshiyasu Shingai, Department of Health and Human Services, Medical Advancement Division, Saitama Prefecture; Tomimasa Sunagawa, Hayato Fujii, Hiroshi Takahashi, Takaaki Ohyama, Michael H. Kramer, and Nobuhiko Okabe, Field Epidemiology Training Program, Infectious Diseases Surveillance Center, NIID

Return to the TopPage

Back to Home