German health officials finally confirmed Friday that the deadly E. coli outbreak, causing a panic across the globe by blanketing Europe and killing 31 people, can be traced to contaminated bean sprouts grown at an organic farm in northern Germany. But authorities are still puzzled as to how the deadly bacteria got there.
Speaking at a news conference in Berlin on Friday, Robert Koch Institute (RKI) President Reinhard Burger told reporters, "It is the sprouts."
This new evidence was gathered during the third case study that focused more on salad ingredients, according to the Center for Infectious Disease Research and Policy.
RKI researchers say they could not completely confirm sprouts as the culprit in the first tests because just 28 percent of patients had reported eating them.
Burger said new interviews with patients point to the consumption of sprouts as the cause of the epidemic. He also said that people who reported eating the suspect sprouts were nine times more likely to have developed bloody diarrhea than those who said they did not eat them.
“We are currently completing a thousand samples of research,” Burger told reporters.
The locally grown sprouts from the organic farm in Lower Saxony touched off the massive E. coli outbreak in May, sickening nearly 3,000. The bacteria strain ultimately made its way to the United States affecting at least four people.
Critics say German investigators got sidetracked when their early tests implicated cucumbers, tomatoes and lettuce, and then cucumbers imported from Spain were found to be contaminated with E. coli – although further testing revealed it was not the outbreak strain.
Epidemiologists outside of Germany who have dealt with sprouts-related outbreaks say sprouts should have been tagged as "a vegetable of interest" from the beginning and that the outbreak was not considered “urgent” by many health officials.
Researchers say sprouts have always been a high-risk food, which are susceptible to contamination.
The warm, moist growing conditions for sprouts also favor the growth of bacteria, yet they've become such a traditional garnish that patients often don't remember eating them.
Craig Hedberg, PhD, a foodborne disease expert at the University of Minnesota, said a food item like sprouts can appear inconspicuously in salads or sandwiches.
“Sprouts can also pose a cross-contamination risk. Who hasn't been to a salad bar and seen alfalfa sprouts in many of the neighboring ingredient containers?" he said.
Beth Kautz, PhD, director of language instruction in the University of Minnesota's German, Scandinavian, and Dutch department, said Germans like making mixed vegetable salads, which can include any of a variety of sprouts but typically do not include iceberg lettuce.
The largest outbreak of E. coli O157:H7 on record occurred in 1996 in Sakai, Japan, and was said to be caused by tainted sprouts. Radish sprouts in school lunches prepared in a central kitchen were epidemiologically linked to the 12,680 illnesses among students, teachers and school staff.
Fresh sprouts are one of the few foods that the U.S. Centers for Disease Control and Prevention and FDA advise children, the elderly, pregnant women and immune-compromised individuals to avoid eating.
Since 1996, there have been at least 30 reported Salmonella and E. coli outbreaks in the U.S. associated with different types of raw and lightly cooked sprouts.
In many of the outbreaks, according to the public health authorities, the sprout seeds have been the source of the harmful bacteria.
To reduce the chance of bacteria-related illness, sprouts need to be cooked thoroughly. The CDC suggests consumers request that raw sprouts of any kind including alfalfa, clover, radish and mung bean sprouts not be added to food such as salads and sandwiches.