Recent outbreaks linked to fresh sprouts remind us that toxic microbes can sometimes travel in small and seemingly healthful packages.
The Japanese need no reminder. They learned the hard way, 15 years ago, when that health-conscious society was gripped by what may be history’s worst outbreak of E. coli O157:H7. The epidemic sickened thousands, most of them children, and killed at least 12.
It also showed critical weaknesses in Japan’s public health system–problems that the government spent years trying to correct.
Up to that time, E. coli O157:H7 was virtually unknown in Japan. Just six small outbreaks had been reported at childcare centers and schools in the five years from 1991 to 1995.
That all changed in mid-July 1996, when health officials in Sakai City, a major port city with a population near a million, received reports of a large number of elementary schoolchildren who had come down with severe diarrhea. The next day, hundreds more sick children and teachers were reported, still more on the next.
Within a week, thousands were ill, hundreds hospitalized, some with hemolytic uremic syndrome (HUS), requiring kidney dialysis. And some were dying.
As doctors and hospitals dealt with the sick, health officials started searching for the source. All the Sakai City patients were students or teachers, and Sakai City shares its water system with neighboring cities where there were no illnesses, so water did not appear to be the problem. These and other circumstances pointed to school lunches, which were prepared at a central facility, then trucked to neighborhood schools across the city.
Meanwhile, the epidemic seemed to be expanding. Workers at a factory in Kyoto, about 30 miles from Sakai City, were showing up at clinics with bloody diarrhea. Several developed HUS. Officials learned that all the patients had eaten in the factory cafeteria.
Something was horribly wrong, but what?
Dr. John Kobayashi, a University of Washington professor and former chief epidemiologist for the state of Washington, was monitoring the outbreak from Seattle and wanted to help. “But the public was in something of a panic, and the Japanese government was embarrassed,” he recalls. “Here they were, the world’s second-richest nation, and then they had this huge outbreak.”
It was terrible timing. A few years earlier, Japan’s booming economy collapsed. Then, in 1995, an earthquake flattened the city of Kobe, not far from Sakai City. A few months later, terrorists released deadly sarin gas in the Tokyo subway, killing 13 people. “They were feeling snakebit,” Kobayashi says.
To make matters worse, Japan’s well-respected health care system was ill-equipped to respond to an outbreak of foodborne illness, Kobayashi says. Their epidemiologists do fine long-term research, but were not trained to respond quickly to an E. coli outbreak.
“Their strategy was to begin a long-term cohort study of 50,000 schoolchildren, which would take forever. They had no experience with field epidemiology.”
American epidemiologists like Kobayashi are accustomed to rapid responses to outbreaks– intensive interviews of victims in an attempt to zero in on the exact source of the illness.
By the time he was contacted by Japanese officials, the epidemic had been going on for weeks, Kobayashi says. And they still didn’t know the source.
Many of the obstacles were cultural. The Sakai City outbreak was enormous because school meals are centrally prepared–an efficient way to feed people, or to distribute foodborne illness. And children are strongly encouraged to eat everything on their plates, which gave field workers few clues to a possible source.
“And the Japanese are reluctant to talk about their illnesses,” Kobayashi says. “The whole idea of officials calling people and asking about their diarrhea is very difficult in Japanese society. And then it is not polite to ask people for the names of other sick people. This is important information to epidemiology, but almost inconceivable in Japanese culture.”
Eventually, the outbreak sickened at least 9,441 people, most of them school children–the worst toll of any recorded outbreak.
Investigators eventually blamed a seemingly unlikely source–radish sprouts, produced by a single Japanese farm and served with school lunches along with cooked chicken and noodles. The sprouts were fingered by a process of elimination. No E. coli was found on samples, but the sprouts were served raw, while most other ingredients were cooked.
Sprouts are susceptible to contamination because they are cultivated with heat and moisture, conditions that also favor E. coli, Salmonella and other microbes, Kobayashi explains. Japanese officials suspected that the contamination originated with the radish seeds, which had been grown and shipped from Oregon.
“But it’s not clear,” Kobayashi adds. “Who knows? The investigation took so long that, by the time samples were taken, everything had been wiped clean.”
Regardless of the source, the outbreak shed light on profound deficiencies with Japan’s public health system, and Kobayashi was hired by the Japanese government to help fix the problem. Over a span of five years, he made frequent trips to Japan, helping train epidemiologists and to redesign their system for responding to foodborne illnesses.
If another major outbreak comes along, he says, the Japanese will be far better prepared.