German government officials lifted their recommendation against eating cucumbers, tomatoes, and lettuce, and showcased evidence that puts sprouts front and center in their investigation of a massive Escherichia coli outbreak, though the outbreak strain has not yet been found in sprouts.
In a joint statement from Robert Koch Institute (RKI), the Federal Institute for Risk Assessment, and the Office of Consumer Protection and Food Safety, the government said findings from early case-control studies were not specific, with one from a cafeteria showing only that enterohemorrhagic E coli (EHEC) infections were linked to eating food from the salad bar. The earliest case-control studies did not ask specifically about sprouts, because too many potential exposures could lead to false positives, the government said.
More extensive case-control studies did ask about sprouts, which were eaten by 30% in one study involving 54 patients and 25% in another study of 24 patients. Another study that matched three healthy controls to each of 26 hemolytic uremic syndrome (HUS) patients found that 25% of the patients had eaten sprouts, compared to 9% of healthy respondents.
Zeroing in on the source
To narrow the possible sources, health officials, once they identified enough restaurant customers, conducted a recipe-based cohort study involving 112 subjects, including 19 who had EHEC infections. The epidemiologic team analyzed menus and restaurant receipts and asked kitchen employees about ingredients and preparation of the food items. “Available photographs taken by travel group members were analyzed to confirm which food items, including toppings, were seen on the plates,” the statement said. That study found that customers who ate sprouts had an 8.6-fold increased likelihood getting sick, and all of the sick participants had eaten sprouts.
A task force assigned to explore distribution chains related to outbreak clusters found that sprouts produced at a Lower Saxony farm were linked to 26 of 55 EHEC disease clusters. Health authorities are exploring the possibility that E coli O104:H4 was transmitted by a human source, that water at the farm was contaminated, or that the sprout seeds were contaminated. Federal officials said lab analysis of environmental samples from the farm is still under way.
“Even if the outbreak pathogen has not been detected in any samples thus far, the accumulated evidence strongly points to this producer as the source of the outbreak,” officials said in the statement.
Federal authorities said they are working to determine if other companies might have contaminated sprout seeds or if other sprout producers could be linked to the outbreak. They urged consumers to avoid eating raw sprouts until the investigation into the source of the pathogen is completed.
Rise in illnesses slows
The European Centre for Disease Prevention and Control (ECDC) in its latest update today said 2,287 EHEC cases have been reported from EU countries, as well as 795 cases of HUS. Thirty-one deaths have been linked to the outbreak. The total represents 145 more infections, 38 more HUS cases, and four more deaths since yesterday.
German officials said in their statement today that several surveillance systems are showing a decline in the number of new EHEC cases, as well as a falling proportion of infections in women. It said the decline could be due to a drop in vegetable consumption, which would have a carryover effect on sprouts, or to a gradual disappearance of the contamination source.
‘An interesting microbe’
David Acheson, MD, served as associate commissioner of foods at the US Food and Drug Administration (FDA) during several high-profile foodborne illness outbreaks, spent several years conducting molecular biologic research on STEC and other foodborne pathogens, said the developments with the outbreak strain are interesting, but not shocking. The E coli O104:H4 outbreak strain shares virulence characteristics of both STEC and enteroaggregative E coli (EAEC). He said scientists have known since the mid 1980s that the genetic information that encodes toxins can move around among different E coli types. “What we’ve seen is an inevitable evolution. That’s what bacteria like to do,” he said.
In this case, an EAEC has acquired a toxin gene to become more virulent. Without the toxin, EAEC types are known to cause low-grade chronic diarrhea, and they can play a malnutrition role in developing countries, Acheson said. He speculates that the E coli O104: H4 is either producing more toxin or is finding a more efficient way to deliver toxin to the bloodstream.
So far the antibiotic resistance seen in the E coli O104:H4 outbreak strain doesn’t appear to play a role in its virulence or to affect clinical treatment; however, it provides a clue that “the bacteria spent a big piece of its life in an environment where antibiotics were floating around,” he said.