SAPPORO - At least five people were confirmed to have died in a mass outbreak of E. coli O-157 food poisoning in Hokkaido as of Monday, with 110 others likely suffering from O-157 contaminated Chinese cabbage pickles.
In addition to the five confirmed fatalities, two elderly women who were residents at a nursing home in Ebetsu, which is near Sapporo, have died after developing symptoms of food poisoning. However, O-157 bacteria has yet to be confirmed as the cause of their deaths. At least three other residents at the same facility have been hospitalized with serious symptoms.
It is strongly believed that the source of the O-157 outbreak was lightly pickled Chinese cabbage. The Sapporo-based food company that processed the cabbage is suspected of failing to properly sterilize the cabbage by heating.
Many details regarding how the E. coli O-157 infections reached epidemic proportions have yet to be clarified. One possible factor behind the mass food poisoning is a method of using less salt when pickling vegetables to suit consumer tastes.
Washing water uncontaminated
One of the four fatalities in the area under the jurisdiction of the Sapporo Health Center was Ayana Matsumura, a 4-year-old girl who died Aug. 11 after developing symptoms of E. coli infection such as stomachaches and diarrhoea due to intestinal bleeding.
Lightly pickled Chinese cabbage was a favourite food among the girl's family and was served on the dining table almost every day, her grandfather, Akira Watanabe, said.
"We never thought pickled vegetables could cause food poisoning and feel extremely sorry that Ayana lost her life when the rest of our family [who also ate the same pickled cabbage] did not fall ill," Watanabe said.
The pickled Chinese cabbage in question was produced by the food company Iwai Shokuhin in Sapporo.
The company shipped about 270 kilograms of pickled Chinese cabbage on July 29 and 30.
From Aug. 11 to 19, cases or suspected cases of O-157 poisoning were reported at nine out of 10 nursing care facilities in and around Sapporo that served the pickles.
Many of the fatalities were people aged 80 or older who were prone to falling ill, health officials said.
Iwai Shokuhin also shipped some pickled cabbage products to local supermarkets and restaurants, including the shop where the Matsumura family bought the tainted pickled cabbage that claimed Ayana's life.
The company said it produced the pickled cabbage by first washing the vegetables with water before soaking them in an antiseptic solution for 10 minutes. The vegetables were then washed a second time.
The products were shipped after the cabbage was pickled for 24 hours in brine mixed with acidic ingredients, company officials said.
The contaminated pickled cabbage was made Saturday. The amount produced on that day was double that of weekdays, the officials said.
Each of the firm's 12 employees in charge of pickling wore masks and gloves. No E. coli bacillus were found in groundwater used for washing purposes in a checkup conducted after the incident, the officials said.
Officials at the Sapporo municipal health centre said they will investigate whether the bacteria came from mud attached to cabbage that was not fully sterilized.
Health centre officials also noted that Iwai Shokuhin failed to record the concentration of the antiseptic solution, raising suspicions that the sterilization process may have been insufficient.
The Hokkaido prefectural government and the Sapporo municipal government have launched on-the-spot investigations of about 590 pickling facilities in Hokkaido under the Food Sanitation Law.
The two governments are scheduled to release a report on the mass O-157 poisoning in early September after completing their investigations.
Cattle dung a possible cause
Mass poisoning caused by lightly pickled vegetables occurred in Saitama Prefecture in 2000, resulting in a single death, and in 2005 in Kagawa Prefecture, which resulted in five deaths. All fatalities were elderly residents of nursing care facilities.
In 2002, more than 100 boys and girls at a nursery in Fukuoka were infected with O-157. The incident was traced back to lightly pickled cucumbers.
"It's possible that O-157 could get mixed with vegetables through fertilizers such as cattle dung," said Prof. Shinichi Yoshida of Kyushu University, a bacteriology expert who participated in probes regarding the poisonings.
"The E. coli O-157 bacteria wouldn't be killed it if were soaked in brine with a salt concentration similar to seawater, or about 3 per cent," he added.
Vegetables pickled in a fermented mixture of rice bran and brine have relatively high pH readings of about 3.5, which indicates a considerably high acidity that is conducive to killing bacteria, Yoshida said.
In recent years, however, many consumers prefer low-sodium processed foods and they tend to shy away from highly acidic pickles, Yoshida explained.
Since the salt concentration of lightly pickled vegetables hover around 2 to 3 per cent and have less acidic pH readings of about 5, they are more likely to be contaminated, he said.
Associate Prof. Takashi Someya of Saga University, an expert in soil microbiology, warned that if compost containing cattle dung is not properly fermented, O-157 is more likely to contaminate vegetables.
Someya said the government should set safety standards regarding the maximum amount of bacteria allowed in cattle dung, which would force cattle farmers to more closely monitor their livestock.