Jun 10, 2011 (CIDRAP News) – German government officials today 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 three federal agencies that have had a role in the investigation, the government said findings from early case-control studies weren't specific, with one from a cafeteria showing only that enterohemorrhagic E coli (EHEC) infections were linked to eating food from the salad bar. The federal agencies were the Robert Koch Institute (RKI), the Federal Institute for Risk Assessment, and the Office of Consumer Protection and Food Safety.
The earliest case-control studies didn't 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 4 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.
Former FDA expert decries slowness of probe
David Acheson, MD, served as associate commissioner of foods at the US Food and Drug Administration (FDA) during several high-profile foodborne illness outbreaks, including a 2008 Salmonella episode in which officials first suspected tomatoes, then later tied the contamination to jalapeno and Serrano peppers. Though he knows what it's like to face criticism of outbreak responses, Acheson told CIDRAP News that the most unfortunate aspect of the German investigation is that has gone so slowly. Acheson is now managing director of food import safety at Leavitt Partners, a consultant group based in Salt Lake City.
"The time they've taken to identify a source has resulted in more exposures than we've needed to have," he said, adding that he was surprised that they didn't suspect sprouts more strongly early in the investigation, given their history in other Shiga-toxin E coli (STEC) outbreaks. According to a report yesterday from the Robert Koch Institute, the most recent onset of diarrhea with and without HUS was Jun 6.
The geographic distribution of the sick patients, focused in northern Germany, should have provided a strong earkt clue that the contaminated source was locally grown, Acheson said.
US officials ran into delays identifying hot peppers as the Salmonella outbreak source, but luckily the pathogen wasn't as virulent as the E coli O104:H4 strain in Europe, Acheson said.
German officials have come under fire from several food safety experts for muddling the risk message to consumers, wrongly flagging Spanish cucumbers, expanding the warning to tomatoes and lettuce, and then sending what appeared to be conflicting messages about sprouts.
Acheson said the messaging might have been driven by the severity of the E coli O104:H4 and shockingly high proportion of HUS cases. For example, he said an outbreak involving a high-morbidity illness like botulism would rightly provoke an early and urgent message to the public about food risks.
Authorities in Germany face extra challenges at this late stage of the investigation, he said. Most of the implicated produce has already been consumed or thrown away, and facilities have had time to clean, which makes it less likely for officials to find hard evidence. Some of the illnesses are likely to be secondary cases, which can be a confounder, and after 2 or 3 weeks people's memories of what they ate can fade.
'An interesting microbe'
Acheson, who 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.
Lessons for the US
"The big picture is that it happened once, and it will happen again," Acheson said, emphasizing that a similar type of pathogen could evolve and have public health consequences in the United States. He said the threat underscores the importance of preventive controls and a well-funded response that allows local and state health departments to do the epidemiologic footwork needed to track down and mitigate a disease outbreak like what Germany is experiencing now.
Germany's EHEC outbreak should be a wake-up call to revisit foodborne pathogen treatments such as irradiation, Acheson said, adding that the tools shouldn't be mandated, but rather become more available to food processors.
Jun 10 German government press release
Jun 10 ECDC update
Jun 9 RKI report