tokyo

Scientists from the US Food and Drug Administration (FDA) are contesting a claim by Japan's health ministry that radish sprout seeds imported from the United States were to blame for last year's food poisoning outbreak caused by the O-157 strain of Escherichia coli. FDA scientists are seeking consultations with ministry officials over the issue.

A report from the ministry's Food Sanitation Investigation Council concludes that an outbreak of food poisoning last March in Aichi and Kanagawa prefectures, which affected 115 people, was caused by eating white radish sprouts grown from contaminated seeds imported from Oregon.

The report says the O-157 E. coli bacterium was not found in the seed sample. But the presence of genetic material linked to vero toxin — a byproduct left by the bacterium — as well as genetic fragments claimed to be unique to O-157 E. coli, were detected.

FDA scientists remain unconvinced, arguing that the test results “do not adequately support the finding that the seeds were contaminated with E. coli O-157”. In a statement released by the US Embassy in Tokyo, the FDA points out that the investigation did not involve a direct comparison of O-157 E. coli isolated from patients and samples extracted from the seeds, as would be necessary to conclude that E. coli from the seeds was the likely cause of food poisoning.

Explaining why no trace of the bacterium was detected in the seeds under conventional cultivation, ministry officials say that strains of E. coli other than O-157 proliferate much faster, suppressing the growth of O-157 colonies. Despite announcing its intention to enforce mandatory sterilization of radish sprout seeds before cultivation, Japan's Ministry of Agriculture, Fisheries and Forestry is also sceptical about the health ministry's conclusion. “Vero toxins are also found in bacteria other than O-157 E. coli,” says a spokesman for the agriculture ministry.

“The test results merely suggest the presence of the bacteria in seed samples; they do not verify the cause of the food poisoning outbreak.”

Japanese producers of white radish sprouts say that the health ministry's recent announcement has dealt a new blow to their business. The ministry set off a public health scare in 1996 when it announced that white radish sprouts might be the source of an earlier O-157 food poisoning outbreak in the Osaka area, which affected more than 9,000 people and claimed nine lives (see Nature 382, 567; 1996).

The ministry subsequently came under fire for reaching a hasty and unsubstantiated conclusion. Its announcement forced food distributors to withdraw radish sprouts from shops and restaurants, and drove many farmers to bankruptcy.